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Figure 1.  Flowchart for the Trials Included in the Meta-analysis
Flowchart for the Trials Included in the Meta-analysis

ED indicates erectile dysfunction.

Figure 2.  Forest Plot of the Association Between Placebo and Erectile Disfunction Outcomes
Forest Plot of the Association Between Placebo and Erectile Disfunction Outcomes

Erectile dysfunction outcomes were measured using the Erectile Function Domain of the International Index of Erectile Function. A low to moderate improvement was seen in the placebo arm, as indicated by the bias-corrected standardized mean difference (Hedges g [SE], 0.35 [0.03]; P < .001).

Table 1.  Studies Included in the Meta-analysis
Studies Included in the Meta-analysis
Table 2.  Results From All IIEF Survey Domains Other Than Erectile Functiona
Results From All IIEF Survey Domains Other Than Erectile Functiona
1.
Goldstein  I, Burnett  AL, Rosen  RC, Park  PW, Stecher  VJ.  The serendipitous story of sildenafil: an unexpected oral therapy for erectile dysfunction.  Sex Med Rev. 2019;7(1):115-128. doi:10.1016/j.sxmr.2018.06.005PubMedGoogle ScholarCrossref
2.
Delate  T, Simmons  VA, Motheral  BR.  Patterns of use of sildenafil among commercially insured adults in the United States: 1998-2002.  Int J Impot Res. 2004;16(4):313-318. doi:10.1038/sj.ijir.3901191PubMedGoogle ScholarCrossref
3.
Dean  RC, Lue  TF.  Physiology of penile erection and pathophysiology of erectile dysfunction.  Urol Clin North Am. 2005;32(4):379-395, v. v. doi:10.1016/j.ucl.2005.08.007PubMedGoogle ScholarCrossref
4.
Yafi  FA, Jenkins  L, Albersen  M,  et al.  Erectile dysfunction.  Nat Rev Dis Primers. 2016;2:16003. doi:10.1038/nrdp.2016.3PubMedGoogle ScholarCrossref
5.
Rosen  RC, Riley  A, Wagner  G, Osterloh  IH, Kirkpatrick  J, Mishra  A.  The international index of erectile function (IIEF): a multidimensional scale for assessment of erectile dysfunction.  Urology. 1997;49(6):822-830. doi:10.1016/S0090-4295(97)00238-0PubMedGoogle ScholarCrossref
6.
Pastuszak  AW.  Current diagnosis and management of erectile dysfunction.  Curr Sex Health Rep. 2014;6(3):164-176. doi:10.1007/s11930-014-0023-9PubMedGoogle ScholarCrossref
7.
Corona  G, Lee  DM, Forti  G,  et al; EMAS Study Group.  Age-related changes in general and sexual health in middle-aged and older men: results from the European Male Ageing Study (EMAS).  J Sex Med. 2010;7(4, pt 1):1362-1380. doi:10.1111/j.1743-6109.2009.01601.xPubMedGoogle ScholarCrossref
8.
Benedetti  F, Carlino  E, Pollo  A.  How placebos change the patient’s brain.  Neuropsychopharmacology. 2011;36(1):339-354. doi:10.1038/npp.2010.81PubMedGoogle ScholarCrossref
9.
Sauro  MD, Greenberg  RP.  Endogenous opiates and the placebo effect: a meta-analytic review.  J Psychosom Res. 2005;58(2):115-120. doi:10.1016/j.jpsychores.2004.07.001PubMedGoogle ScholarCrossref
10.
Amanzio  M, Benedetti  F.  Neuropharmacological dissection of placebo analgesia: expectation-activated opioid systems versus conditioning-activated specific subsystems.  J Neurosci. 1999;19(1):484-494. doi:10.1523/JNEUROSCI.19-01-00484.1999PubMedGoogle ScholarCrossref
11.
Benedetti  F, Amanzio  M, Rosato  R, Blanchard  C.  Nonopioid placebo analgesia is mediated by CB1 cannabinoid receptors.  Nat Med. 2011;17(10):1228-1230. doi:10.1038/nm.2435PubMedGoogle ScholarCrossref
12.
de la Fuente-Fernández  R, Lidstone  S, Stoessl  AJ.  Placebo effect and dopamine release.  J Neural Transm Suppl. 2006;(70):415-418.PubMedGoogle Scholar
13.
de la Fuente-Fernández  R.  The placebo-reward hypothesis: dopamine and the placebo effect.  Parkinsonism Relat Disord. 2009;15(suppl 3):S72-S74. doi:10.1016/S1353-8020(09)70785-0PubMedGoogle ScholarCrossref
14.
Wager  TD, Rilling  JK, Smith  EE,  et al.  Placebo-induced changes in FMRI in the anticipation and experience of pain.  Science. 2004;303(5661):1162-1167. doi:10.1126/science.1093065PubMedGoogle ScholarCrossref
15.
Geuter  S, Eippert  F, Hindi Attar  C, Büchel  C.  Cortical and subcortical responses to high and low effective placebo treatments.  Neuroimage. 2013;67:227-236. doi:10.1016/j.neuroimage.2012.11.029PubMedGoogle ScholarCrossref
16.
Jadad  AR, Moore  RA, Carroll  D,  et al.  Assessing the quality of reports of randomized clinical trials: is blinding necessary?  Control Clin Trials. 1996;17(1):1-12. doi:10.1016/0197-2456(95)00134-4PubMedGoogle ScholarCrossref
17.
Albuquerque  DC, Miziara  LJ, Saraiva  JF, Rodrigues  US, Ribeiro  AB, Wajngarten  M.  Efficacy, safety and tolerability of sildenafil in Brazilian hypertensive patients on multiple antihypertensive drugs.  Int Braz J Urol. 2005;31(4):342-353. doi:10.1590/S1677-55382005000400008PubMedGoogle ScholarCrossref
18.
Althof  SE, O’leary  MP, Cappelleri  JC,  et al; International SEAR Study Group.  Sildenafil citrate improves self-esteem, confidence, and relationships in men with erectile dysfunction: results from an international, multi-center, double-blind, placebo-controlled trial.  J Sex Med. 2006;3(3):521-529. doi:10.1111/j.1743-6109.2006.00234.xPubMedGoogle ScholarCrossref
19.
Bénard  F, Carrier  S, Lee  JC, Talwar  V, Defoy  I.  Men with mild erectile dysfunction benefit from sildenafil treatment.  J Sex Med. 2010;7(11):3725-3735. doi:10.1111/j.1743-6109.2010.02015.xPubMedGoogle ScholarCrossref
20.
Carrier  S, Brock  GB, Pommerville  PJ,  et al.  Efficacy and safety of oral tadalafil in the treatment of men in Canada with erectile dysfunction: a randomized, double-blind, parallel, placebo-controlled clinical trial.  J Sex Med. 2005;2(5):685-698. doi:10.1111/j.1743-6109.2005.00097.xPubMedGoogle ScholarCrossref
21.
Chen  KK, Jiann  BP, Lin  JS,  et al.  Efficacy and safety of on-demand oral tadalafil in the treatment of men with erectile dysfunction in Taiwan: a randomized, double-blind, parallel, placebo-controlled clinical study.  J Sex Med. 2004;1(2):201-208. doi:10.1111/j.1743-6109.2004.04029.xPubMedGoogle ScholarCrossref
22.
Chung  JH, Kang  DH, Oh  CY,  et al.  Safety and efficacy of once daily administration of 50 mg mirodenafil in patients with erectile dysfunction: a multicenter, double-blind, placebo controlled trial.  J Urol. 2013;189(3):1006-1013. doi:10.1016/j.juro.2012.08.243PubMedGoogle Scholar
23.
Eardley  I, Gentile  V, Austoni  E,  et al.  Efficacy and safety of tadalafil in a Western European population of men with erectile dysfunction.  BJU Int. 2004;94(6):871-877. doi:10.1111/j.1464-410X.2004.05049.xPubMedGoogle Scholar
24.
Egerdie  RB, Auerbach  S, Roehrborn  CG,  et al.  Tadalafil 2.5 or 5 mg administered once daily for 12 weeks in men with both erectile dysfunction and signs and symptoms of benign prostatic hyperplasia: results of a randomized, placebo-controlled, double-blind study.  J Sex Med. 2012;9(1):271-281. doi:10.1111/j.1743-6109.2011.02504.xPubMedGoogle Scholar
25.
Evliyaoğlu  Y, Yelsel  K, Kobaner  M, Alma  E, Saygılı  M.  Efficacy and tolerability of tadalafil for treatment of erectile dysfunction in men taking serotonin reuptake inhibitors.  Urology. 2011;77(5):1137-1141. doi:10.1016/j.urology.2010.12.036PubMedGoogle Scholar
26.
Zonana Farca  E, Francolugo-Vélez  V, Moy-Eransus  C, Orozco Bravo  A, Tseng  LJ, Stecher  VJ.  Self-esteem, confidence and relationship satisfaction in men with erectile dysfunction: a randomized, parallel-group, double-blind, placebo-controlled study of sildenafil in Mexico.  Int J Impot Res. 2008;20(4):402-408. doi:10.1038/ijir.2008.24PubMedGoogle Scholar
27.
Fawzi  A, Kamel  M, Salem  E,  et al.  Sildenafil citrate in combination with tamsulosin versus tamsulosin monotherapy for management of male lower urinary tract symptoms due to benign prostatic hyperplasia: a randomised, double-blind, placebo-controlled trial.  Arab J Urol. 2016;15(1):53-59. doi:10.1016/j.aju.2016.11.001PubMedGoogle Scholar
28.
Gacci  M, Vittori  G, Tosi  N,  et al.  A randomized, placebo-controlled study to assess safety and efficacy of vardenafil 10 mg and tamsulosin 0.4 mg vs. tamsulosin 0.4 mg alone in the treatment of lower urinary tract symptoms secondary to benign prostatic hyperplasia.  J Sex Med. 2012;9(6):1624-1633. doi:10.1111/j.1743-6109.2012.02718.xPubMedGoogle Scholar
29.
Gittelman  M, McMahon  CG, Rodríguez-Rivera  JA, Beneke  M, Ulbrich  E, Ewald  S.  The POTENT II randomised trial: efficacy and safety of an orodispersible vardenafil formulation for the treatment of erectile dysfunction.  Int J Clin Pract. 2010;64(5):594-603. doi:10.1111/j.1742-1241.2010.02358.xPubMedGoogle Scholar
30.
Giuliano  F, Oelke  M, Jungwirth  A,  et al.  Tadalafil once daily improves ejaculatory function, erectile function, and sexual satisfaction in men with lower urinary tract symptoms suggestive of benign prostatic hyperplasia and erectile dysfunction: results from a randomized, placebo- and tamsulosin-controlled, 12-week double-blind study.  J Sex Med. 2013;10(3):857-865. doi:10.1111/jsm.12039PubMedGoogle Scholar
31.
Glina  S, Damião  R, Abdo  C, Afif-Abdo  J, Tseng  LJ, Stecher  V.  Self-esteem, confidence, and relationships in Brazilian men with erectile dysfunction receiving sildenafil citrate: a randomized, parallel-group, double-blind, placebo-controlled study in Brazil.  J Sex Med. 2009;6(1):268-275. doi:10.1111/j.1743-6109.2008.01026.xPubMedGoogle Scholar
32.
Glina  S, Toscano  I, Gomatzky  C,  et al.  Efficacy and tolerability of lodenafil carbonate for oral therapy in erectile dysfunction: a phase II clinical trial.  J Sex Med. 2009;6(2):553-557. doi:10.1111/j.1743-6109.2008.01079.xPubMedGoogle Scholar
33.
Glina  S, Fonseca  GN, Bertero  EB,  et al.  Efficacy and tolerability of lodenafil carbonate for oral therapy of erectile dysfunction: a phase III clinical trial.  J Sex Med. 2010;7(5):1928-1936. doi:10.1111/j.1743-6109.2010.01711.xPubMedGoogle Scholar
34.
Heiman  JR, Talley  DR, Bailen  JL,  et al.  Sexual function and satisfaction in heterosexual couples when men are administered sildenafil citrate (Viagra) for erectile dysfunction: a multicentre, randomised, double-blind, placebo-controlled trial.  BJOG. 2007;114(4):437-447. doi:10.1111/j.1471-0528.2006.01228.xPubMedGoogle Scholar
35.
Hellstrom  WJ, Kaminetsky  J, Belkoff  LH,  et al.  Efficacy of avanafil 15 minutes after dosing in men with erectile dysfunction: a randomized, double-blind, placebo controlled study.  J Urol. 2015;194(2):485-492. doi:10.1016/j.juro.2014.12.101PubMedGoogle Scholar
36.
Jones  LA, Klimberg  IW, McMurray  JG, Padula  R, Tseng  LJ, Stecher  VJ.  Effect of sildenafil citrate on the male sexual experience assessed with the Sexual Experience Questionnaire: a multicenter, double-blind, placebo-controlled trial with open-label extension.  J Sex Med. 2008;5(8):1955-1964. doi:10.1111/j.1743-6109.2008.00879.xPubMedGoogle Scholar
37.
Kadioglu  A, Grohmann  W, Depko  A, Levinson  IP, Sun  F, Collins  S.  Quality of erections in men treated with flexible-dose sildenafil for erectile dysfunction: multicenter trial with a double-blind, randomized, placebo-controlled phase and an open-label phase.  J Sex Med. 2008;5(3):726-734. doi:10.1111/j.1743-6109.2007.00701.xPubMedGoogle Scholar
38.
Kim  ED, Seftel  AD, Goldfischer  ER, Ni  X, Burns  PR.  A return to normal erectile function with tadalafil once daily after an incomplete response to as-needed PDE5 inhibitor therapy.  J Sex Med. 2014;11(3):820-830. doi:10.1111/jsm.12253PubMedGoogle Scholar
39.
Mahon  A, Sidhu  PS, Muir  G, Macdougall  IC.  The efficacy of sildenafil for the treatment of erectile dysfunction in male peritoneal dialysis patients.  Am J Kidney Dis. 2005;45(2):381-387. doi:10.1053/j.ajkd.2004.10.012PubMedGoogle Scholar
40.
Martin-Morales  A, Meijide  F, García  N, Artes  M, Muñoz  A.  Efficacy of vardenafil and influence on self-esteem and self-confidence in patients with severe erectile dysfunction.  J Sex Med. 2007;4(2):440-447. doi:10.1111/j.1743-6109.2006.00426.xPubMedGoogle Scholar
41.
Pattanaik  S, Kaundal  P, Mavuduru  RS, Singh  SK, Mandal  AK.  Endothelial dysfunction in patients with erectile dysfunction: a double-blind, randomized-control trial using tadalafil.  Sex Med. 2019;7(1):41-47. doi:10.1016/j.esxm.2018.11.008PubMedGoogle Scholar
42.
McCullough  AR, Steidle  CP, Klee  B, Tseng  LJ.  Randomized, double-blind, crossover trial of sildenafil in men with mild to moderate erectile dysfunction: efficacy at 8 and 12 hours postdose.  Urology. 2008;71(4):686-692. doi:10.1016/j.urology.2007.12.025PubMedGoogle Scholar
43.
McMahon  CG, Stuckey  BG, Lording  DW,  et al.  A 6-month study of the efficacy and safety of tadalafil in the treatment of erectile dysfunction: a randomised, double-blind, parallel-group, placebo-controlled study in Australian men.  Int J Clin Pract. 2005;59(2):143-149. doi:10.1111/j.1742-1241.2005.00451.xPubMedGoogle Scholar
44.
McVary  KT, Roehrborn  CG, Kaminetsky  JC,  et al.  Tadalafil relieves lower urinary tract symptoms secondary to benign prostatic hyperplasia.  J Urol. 2007;177(4):1401-1407. doi:10.1016/j.juro.2006.11.037PubMedGoogle Scholar
45.
McVary  KT, Monnig  W, Camps  JL  Jr, Young  JM, Tseng  LJ, van den Ende  G.  Sildenafil citrate improves erectile function and urinary symptoms in men with erectile dysfunction and lower urinary tract symptoms associated with benign prostatic hyperplasia: a randomized, double-blind trial.  J Urol. 2007;177(3):1071-1077. doi:10.1016/j.juro.2006.10.055PubMedGoogle Scholar
46.
Meuleman  E, Cuzin  B, Opsomer  RJ,  et al.  A dose-escalation study to assess the efficacy and safety of sildenafil citrate in men with erectile dysfunction.  BJU Int. 2001;87(1):75-81. doi:10.1046/j.1464-410x.2001.00998.xPubMedGoogle Scholar
47.
Miner  M, Gilderman  L, Bailen  J,  et al.  Vardenafil in men with stable statin therapy and dyslipidemia.  J Sex Med. 2008;5(6):1455-1467. doi:10.1111/j.1743-6109.2008.00820.xPubMedGoogle Scholar
48.
Moncada  I, Martínez-Jabaloyas  JM, Rodriguez-Vela  L,  et al.  Emotional changes in men treated with sildenafil citrate for erectile dysfunction: a double-blind, placebo-controlled clinical trial.  J Sex Med. 2009;6(12):3469-3477. doi:10.1111/j.1743-6109.2009.01514.xPubMedGoogle Scholar
49.
Moon  KH, Ko  YH, Kim  SW,  et al.  Efficacy of once-daily administration of udenafil for 24 weeks on erectile dysfunction: results from a randomized multicenter placebo-controlled clinical trial.  J Sex Med. 2015;12(5):1194-1201. doi:10.1111/jsm.12862PubMedGoogle Scholar
50.
Nunes  LV, Lacaz  FS, Bressan  RA, Nunes  SO, Mari  JdeJ.  Adjunctive treatment with lodenafil carbonate for erectile dysfunction in outpatients with schizophrenia and spectrum: a randomized, double-blind, crossover, placebo-controlled trial.  J Sex Med. 2013;10(4):1136-1145. doi:10.1111/jsm.12040PubMedGoogle Scholar
51.
Nurnberg  HG, Hensley  PL, Gelenberg  AJ, Fava  M, Lauriello  J, Paine  S.  Treatment of antidepressant-associated sexual dysfunction with sildenafil: a randomized controlled trial.  JAMA. 2003;289(1):56-64. doi:10.1001/jama.289.1.56PubMedGoogle Scholar
52.
Orr  G, Weiser  M, Polliack  M, Raviv  G, Tadmor  D, Grunhaus  L.  Effectiveness of sildenafil in treating erectile dysfunction in PTSD patients: a double-blind, placebo-controlled crossover study.  J Clin Psychopharmacol. 2006;26(4):426-430. doi:10.1097/01.jcp.0000227701.33999.b3PubMedGoogle Scholar
53.
Ortaç  M, Çayan  S, Çalişkan  MK,  et al.  Efficacy and tolerability of udenafil in Turkish men with erectile dysfunction of psychogenic and organic aetiology: a randomized, double-blind, placebo-controlled study.  Andrology. 2013;1(4):549-555. doi:10.1111/j.2047-2927.2013.00085.xPubMedGoogle Scholar
54.
Paick  JS, Kim  SW, Yang  DY,  et al.  The efficacy and safety of udenafil, a new selective phosphodiesterase type 5 inhibitor, in patients with erectile dysfunction.  J Sex Med. 2008;5(4):946-953. doi:10.1111/j.1743-6109.2007.00723.xPubMedGoogle Scholar
55.
Paick  JS, Ahn  TY, Choi  HK,  et al.  Efficacy and safety of mirodenafil, a new oral phosphodiesterase type 5 inhibitor, for treatment of erectile dysfunction.  J Sex Med. 2008;5(11):2672-2680. doi:10.1111/j.1743-6109.2008.00945.xPubMedGoogle Scholar
56.
Paick  JS, Kim  JJ, Kim  SC,  et al.  Efficacy and safety of mirodenafil in men taking antihypertensive medications.  J Sex Med. 2010;7(9):3143-3152. doi:10.1111/j.1743-6109.2010.01926.xPubMedGoogle Scholar
57.
Park  HJ, Park  JK, Park  K, Min  K, Park  NC.  Efficacy of udenafil for the treatment of erectile dysfunction up to 12 hours after dosing: a randomized placebo-controlled trial.  J Sex Med. 2010;7(6):2209-2216. doi:10.1111/j.1743-6109.2010.01817.xPubMedGoogle Scholar
58.
Park  HJ, Choi  HK, Ahn  TY,  et al.  Efficacy and safety of oral mirodenafil in the treatment of erectile dysfunction in diabetic men in Korea: a multicenter, randomized, double-blind, placebo-controlled clinical trial.  J Sex Med. 2010;7(8):2842-2850. doi:10.1111/j.1743-6109.2010.01888.xPubMedGoogle Scholar
59.
Park  SY, Choi  GS, Park  JS, Kim  HJ, Park  JA, Choi  JI.  Efficacy and safety of udenafil for the treatment of erectile dysfunction after total mesorectal excision of rectal cancer: a randomized, double-blind, placebo-controlled trial.  Surgery. 2015;157(1):64-71. doi:10.1016/j.surg.2014.07.007PubMedGoogle Scholar
60.
Park  HJ, Kim  SW, Kim  JJ,  et al.  A randomized, placebo-controlled, double-blind, multi-center therapeutic confirmatory study to evaluate the safety and efficacy of avanafil in Korean patients with erectile dysfunction.  J Korean Med Sci. 2017;32(6):1016-1023. doi:10.3346/jkms.2017.32.6.1016PubMedGoogle Scholar
61.
Porst  H, Rosen  R, Padma-Nathan  H,  et al.  The efficacy and tolerability of vardenafil, a new, oral, selective phosphodiesterase type 5 inhibitor, in patients with erectile dysfunction: the first at-home clinical trial.  Int J Impot Res. 2001;13(4):192-199. doi:10.1038/sj.ijir.3900713PubMedGoogle Scholar
62.
Porst  H, Kim  ED, Casabé  AR,  et al; LVHJ study team.  Efficacy and safety of tadalafil once daily in the treatment of men with lower urinary tract symptoms suggestive of benign prostatic hyperplasia: results of an international randomized, double-blind, placebo-controlled trial.  Eur Urol. 2011;60(5):1105-1113. doi:10.1016/j.eururo.2011.08.005PubMedGoogle Scholar
63.
Rosen  RC, Wincze  J, Mollen  MD, Gondek  K, McLeod  LD, Fisher  WA.  Responsiveness and minimum important differences for the erection quality scale.  J Urol. 2007;178(5):2076-2081. doi:10.1016/j.juro.2007.07.019PubMedGoogle Scholar
64.
Safarinejad  MR, Kolahi  AA, Ghaedi  G.  Safety and efficacy of sildenafil citrate in treating erectile dysfunction in patients with combat-related post-traumatic stress disorder: a double-blind, randomized and placebo-controlled study.  BJU Int. 2009;104(3):376-383. doi:10.1111/j.1464-410X.2009.08560.xPubMedGoogle Scholar
65.
Santi  D, Granata  AR, Guidi  A,  et al.  Six months of daily treatment with vardenafil improves parameters of endothelial inflammation and of hypogonadism in male patients with type 2 diabetes and erectile dysfunction: a randomized, double-blind, prospective trial.  Eur J Endocrinol. 2016;174(4):513-522. doi:10.1530/EJE-15-1100PubMedGoogle Scholar
66.
Saylan  M, Khalaf  I, Kadioglu  A,  et al.  Efficacy of tadalafil in Egyptian and Turkish men with erectile dysfunction.  Int J Clin Pract. 2006;60(7):812-819. doi:10.1111/j.1742-1241.2006.00993.xPubMedGoogle Scholar
67.
Seftel  AD, Wilson  SK, Knapp  PM, Shin  J, Wang  WC, Ahuja  S.  The efficacy and safety of tadalafil in United States and Puerto Rican men with erectile dysfunction.  J Urol. 2004;172(2):652-657. doi:10.1097/01.ju.0000132857.39680.cePubMedGoogle Scholar
68.
Seibel  I, Poli De Figueiredo  CE, Telöken  C, Moraes  JF.  Efficacy of oral sildenafil in hemodialysis patients with erectile dysfunction.  J Am Soc Nephrol. 2002;13(11):2770-2775. doi:10.1097/01.ASN.0000034201.97937.3EPubMedGoogle Scholar
69.
Seidman  SN, Roose  SP, Menza  MA, Shabsigh  R, Rosen  RC.  Treatment of erectile dysfunction in men with depressive symptoms: results of a placebo-controlled trial with sildenafil citrate.  Am J Psychiatry. 2001;158(10):1623-1630. doi:10.1176/appi.ajp.158.10.1623PubMedGoogle Scholar
70.
Shabsigh  R, Kaufman  J, Magee  M, Creanga  D, Russell  D, Budhwani  M.  A multicenter, double-blind, placebo-controlled trial to assess the efficacy of sildenafil citrate in men with unrecognized erectile dysfunction.  Urology. 2010;76(2):373-379. doi:10.1016/j.urology.2010.03.017PubMedGoogle Scholar
71.
Sharma  RK, Prasad  N, Gupta  A, Kapoor  R.  Treatment of erectile dysfunction with sildenafil citrate in renal allograft recipients: a randomized, double-blind, placebo-controlled, crossover trial.  Am J Kidney Dis. 2006;48(1):128-133. doi:10.1053/j.ajkd.2006.04.061PubMedGoogle Scholar
72.
Shim  YS, Pae  CU, Cho  KJ, Kim  SW, Kim  JC, Koh  JS.  Effects of daily low-dose treatment with phosphodiesterase type 5 inhibitor on cognition, depression, somatization and erectile function in patients with erectile dysfunction: a double-blind, placebo-controlled study.  Int J Impot Res. 2014;26(2):76-80. doi:10.1038/ijir.2013.38PubMedGoogle Scholar
73.
Skoumal  R, Chen  J, Kula  K,  et al.  Efficacy and treatment satisfaction with on-demand tadalafil (Cialis) in men with erectile dysfunction.  Eur Urol. 2004;46(3):362-369. doi:10.1016/j.eururo.2004.04.026PubMedGoogle Scholar
74.
Vardi  Y, Appel  B, Ofer  Y, Greunwald  I, Dayan  L, Jacob  G.  Effect of chronic sildenafil treatment on penile endothelial function: a randomized, double-blind, placebo controlled study.  J Urol. 2009;182(6):2850-2855. doi:10.1016/j.juro.2009.08.025PubMedGoogle Scholar
75.
Ziegler  D, Merfort  F, Van Ahlen  H, Yassin  A, Reblin  T, Neureither  M.  Efficacy and safety of flexible-dose vardenafil in men with type 1 diabetes and erectile dysfunction.  J Sex Med. 2006;3(5):883-891. doi:10.1111/j.1743-6109.2006.00295.xPubMedGoogle Scholar
76.
Zelefsky  MJ, Shasha  D, Branco  RD,  et al.  Prophylactic sildenafil citrate improves select aspects of sexual function in men treated with radiotherapy for prostate cancer.  J Urol. 2014;192(3):868-874. doi:10.1016/j.juro.2014.02.097PubMedGoogle Scholar
77.
Incrocci  L, Koper  PC, Hop  WC, Slob  AK.  Sildenafil citrate (Viagra) and erectile dysfunction following external beam radiotherapy for prostate cancer: a randomized, double-blind, placebo-controlled, cross-over study.  Int J Radiat Oncol Biol Phys. 2001;51(5):1190-1195. doi:10.1016/S0360-3016(01)01767-9PubMedGoogle Scholar
78.
Padma-Nathan  H, McCullough  AR, Levine  LA,  et al; Study Group.  Randomized, double-blind, placebo-controlled study of postoperative nightly sildenafil citrate for the prevention of erectile dysfunction after bilateral nerve-sparing radical prostatectomy.  Int J Impot Res. 2008;20(5):479-486. doi:10.1038/ijir.2008.33PubMedGoogle Scholar
79.
Pisansky  TM, Pugh  SL, Greenberg  RE,  et al.  Tadalafil for prevention of erectile dysfunction after radiotherapy for prostate cancer: the Radiation Therapy Oncology Group [0831] randomized clinical trial.  JAMA. 2014;311(13):1300-1307. doi:10.1001/jama.2014.2626PubMedGoogle Scholar
80.
Pfaus  JG.  Pathways of sexual desire.  J Sex Med. 2009;6(6):1506-1533. doi:10.1111/j.1743-6109.2009.01309.xPubMedGoogle Scholar
81.
Montorsi  F, Perani  D, Anchisi  D,  et al.  Brain activation patterns during video sexual stimulation following the administration of apomorphine: results of a placebo-controlled study.  Eur Urol. 2003;43(4):405-411. doi:10.1016/S0302-2838(03)00053-8PubMedGoogle Scholar
82.
Mulhall  JP.  Sublingual apomorphine for the treatment of erectile dysfunction.  Expert Opin Investig Drugs. 2002;11(2):295-302. doi:10.1517/13543784.11.2.295PubMedGoogle Scholar
83.
Montorsi  F, Perani  D, Anchisi  D,  et al.  Apomorphine-induced brain modulation during sexual stimulation: a new look at central phenomena related to erectile dysfunction.  Int J Impot Res. 2003;15(3):203-209. doi:10.1038/sj.ijir.3900999PubMedGoogle Scholar
84.
Melnik  T, Abdo  CH.  Psychogenic erectile dysfunction: comparative study of three therapeutic approaches.  J Sex Marital Ther. 2005;31(3):243-255. doi:10.1080/00926230590513465PubMedGoogle Scholar
85.
McCabe  MP, Price  E, Piterman  L, Lording  D.  Evaluation of an internet-based psychological intervention for the treatment of erectile dysfunction.  Int J Impot Res. 2008;20(3):324-330. doi:10.1038/ijir.2008.3PubMedGoogle Scholar
86.
Aubin  S, Heiman  JR, Berger  RE, Murallo  AV, Yung-Wen  L.  Comparing sildenafil alone vs. sildenafil plus brief couple sex therapy on erectile dysfunction and couples’ sexual and marital quality of life: a pilot study.  J Sex Marital Ther. 2009;35(2):122-143. doi:10.1080/00926230802712319PubMedGoogle Scholar
87.
Kam-Hansen  S, Jakubowski  M, Kelley  JM,  et al.  Altered placebo and drug labeling changes the outcome of episodic migraine attacks.  Sci Transl Med. 2014;6(218):218ra5. doi:10.1126/scitranslmed.3006175PubMedGoogle Scholar
88.
Waber  RL, Shiv  B, Carmon  Z, Ariely  D.  Commercial features of placebo and therapeutic efficacy.  JAMA. 2008;299(9):1016-1017. doi:10.1001/jama.299.9.1016PubMedGoogle Scholar
89.
Khan  A, Redding  N, Brown  WA.  The persistence of the placebo response in antidepressant clinical trials.  J Psychiatr Res. 2008;42(10):791-796. doi:10.1016/j.jpsychires.2007.10.004PubMedGoogle Scholar
90.
Schwartz  EJ, Wong  P, Graydon  RJ.  Sildenafil preserves intracorporeal smooth muscle after radical retropubic prostatectomy.  J Urol. 2004;171(2, pt 1):771-774. doi:10.1097/01.ju.0000106970.97082.61PubMedGoogle Scholar
91.
Raina  R, Lakin  MM, Agarwal  A,  et al.  Long-term effect of sildenafil citrate on erectile dysfunction after radical prostatectomy: 3-year follow-up.  Urology. 2003;62(1):110-115. doi:10.1016/S0090-4295(03)00157-2PubMedGoogle Scholar
92.
Ohebshalom  M, Parker  M, Guhring  P, Mulhall  JP.  The efficacy of sildenafil citrate following radiation therapy for prostate cancer: temporal considerations.  J Urol. 2005;174(1):258-262. doi:10.1097/01.ju.0000164286.47518.1ePubMedGoogle Scholar
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    Original Investigation
    Urology
    March 20, 2020

    Placebo Responses Among Men With Erectile Dysfunction Enrolled in Phosphodiesterase 5 Inhibitor Trials: A Systematic Review and Meta-analysis

    Author Affiliations
    • 1Department of Clinical Neuroscience, Karolinska Institute, Solna, Sweden
    • 2Department of Medicine, Karolinska Institute, Solna, Sweden
    • 3Program in Placebo Studies, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts
    JAMA Netw Open. 2020;3(3):e201423. doi:10.1001/jamanetworkopen.2020.1423
    Key Points español 中文 (chinese)

    Question  Was there an association between placebo and improved erectile function among men enrolled in studies of phosphodiesterase 5 inhibitors?

    Findings  This systematic review and meta-analysis of 12 564 men found a significant association between placebo and improved erectile function, with the effect size being larger among men with posttraumatic stress disorder. There was no difference between response to placebo and phosphodiesterase 5 inhibitors in men with erectile dysfunction after prostate surgery.

    Meaning  The findings suggest that contextual factors are important in the delivery of care to patients with sexual dysfunction, and the lack of difference in response between placebo and phosphodiesterase 5 inhibitors in certain patient subgroups suggests that clinical practice should change.

    Abstract

    Importance  Placebo responses in the treatment of erectile dysfunction (ED) are poorly described in the literature to date.

    Objective  To quantify the association of placebo with ED outcomes among men enrolled in placebo-controlled, phosphodiesterase 5 inhibitor (PDE5I) trials.

    Data Sources  For this systematic review and meta-analysis, a database search was conducted to identify double-blind, placebo-controlled studies using PDE5Is for the treatment of ED published from January 1, 1998, to December 31, 2018, within MEDLINE, Embase, Cochrane Library, and Web of Science. Only articles published in the English language were included.

    Study Selection  Double-blind, placebo-controlled randomized clinical trials of PDE5Is for ED were included. Studies were excluded if they did not provide distribution measures for statistical analysis. Study selection review assessments were conducted by 2 independent investigators. A total of 2215 studies were identified from the database search, and after review, 63 studies that included 12 564 men were analyzed.

    Data Extraction and Synthesis  Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed in abstracting data and assessing validity. Data were extracted from published reports by 2 independent reviewers. Quality assessment was performed using the Jadad scale. Data were pooled using a random-effects model.

    Main Outcomes and Measures  The main outcome was improvement in the erectile function domain of the International Index of Erectile Function questionnaire in the placebo arm of the included studies. Effect size was reported as bias-corrected standardized mean difference (Hedges g). The hypothesis was formulated before data extraction.

    Results  A total of 63 studies that included 12 564 men (mean [SD] age, 55 [7] years; age range, 36-68 years) were included. Erectile function was significantly improved among participants in the placebo arm, with a small to moderate effect size (Hedges g [SE], 0.35 [0.03]; P < .001). Placebo effect size was larger among participants with ED associated with posttraumatic stress disorder (Hedges g [SE], 0.78 [0.32]; P = .02) compared with the overall analysis. No significant difference was found between placebo and PDE5Is for ED after prostate surgery or radiotherapy (Hedges g [SE], 0.30 [0.17]; P = .08).

    Conclusions and Relevance  In this study, placebo was associated with improvement of ED, especially among men with ED-related posttraumatic stress disorder. No difference was found between placebo and PDE5I among men treated for ED after prostate surgery.

    Introduction

    In the past few decades, few drugs have achieved the same mythologic status as sildenafil. Approved in 1998 for treatment of erectile dysfunction (ED), it was soon accompanied by tadalafil and vardenafil, and more recently a few additional drugs within the class of phosphodiesterase 5 inhibitors (PDE5Is) entered the market. Sildenafil was originally developed to relieve symptoms of angina pectoris. What was first considered an adverse effect turned out to be beneficial for increasing blood flow in other areas as well.1 Anecdotes from early clinical trials describe study participants being unwilling to return unused pills because of the positive erectile effects of the study drug. Despite its specific effect on blood flow through relaxing the penile cavernosal smooth muscle cells, the reputation of the drug has become synonymous with potency, increased virility, and improved sexual performance in general. A previous study2 reported that sildenafil and other equivalent drugs have been used recreationally by men (both adults and adolescents) without ED. Given the reputation of this class of drugs, it seems possible that some of the effects of the drugs may be related to the power of belief.

    Erectile function can be divided into a central component that influences the sympathetic outflow from the thoracolumbar region of the spinal cord and a peripheral reflexogenic erectile function mediated by nitrergic nerves that project from the sacral region of the spinal cord.3 Erectile dysfunction can be caused by many adversities, such as cardiovascular disease, diabetes, smoking, hypogonadism, iatrogenesis due to pelvic surgery, and adverse effects of medication, but it can also be of psychogenic origin. It has been estimated that approximately 80% of ED is peripheral in origin, although psychogenic factors is likely associated with ED in these cases too. The severity of ED is commonly diagnosed using the International Index of Erectile Function questionnaire (IIEF).4,5 A previous study6 performed in the United States estimated the prevalence of ED to be 44% to 70% in men 60 years and older, with increased prevalence with advancing age. A European study7 has estimated that ED prevalence ranges from 6% to 64% beginning at 40 years of age and becoming more prevalent in the upper range of the age span.

    In any clinical trial, improvement in the placebo arm is common. Placebo effects have been demonstrated in many conditions, such as Parkinson disease, pain disorders, anxiety disorders, depression, asthma, and irritable bowel syndrome.8 Several neurobiological mechanisms have been proposed to underlie placebo effects, including involvement of endogenous opioids,9,10 endogenous cannabinoids,11 and activation of dopaminergic neurons.12,13 The placebo effect has also been demonstrated in neuroimaging studies,14,15 which have found increased neural activations in brain structures involved in reduction of, for example, pain or motor symptoms.

    We conducted a systematic review and meta-analysis on the use of PDE5Is for ED. The primary goal was to quantify the change in erectile function among patients in the placebo arm of randomized clinical trials as measured by the erectile function domain of the IIEF questionnaire. To our knowledge, this is the first comprehensive meta-analysis that quantifies the association of placebo with ED outcomes in randomized clinical trials of PDE5I.

    Methods
    Data Sources and Searches

    The review protocol was preregistered in the PROSPERO database for meta-analyses (CRD42018109553), including a full account of searches, inclusion and exclusion criteria, main outcomes, and an analysis plan. This study followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline. Data were obtained in collaboration with the Karolinska Institute Library. Searches in MEDLINE, Embase, Cochrane Library, and Web of Science Core Collection were performed for all randomized clinical trials published between January 1, 1998, and December 31, 2018, that focused on PDE5Is for ED treatment.

    The most common measure to evaluate erectile function is the erectile function domain of the IIEF (IIEF-EF). Along with the IIEF-EF, the other domains of the IIEF are orgasmic function (IIEF-OF), intercourse satisfaction (IIEF-IS), sexual desire (IIEF-SD), and overall satisfaction (IIEF-OS). The IIEF-EF domain has a top score of 30, with a score below 14 indicating clinically impaired ED function and recommending use of a PDE5I.4,5 A change of 4 points or more is considered clinically meaningful. The IIEF-EF domain was chosen as the primary outcome of this meta-analysis. Some studies used the abridged 5-question version of the IIEF, Sexual Health Inventory for Men.

    Study Selection

    The selection of studies to be included in our analysis was independently conducted by 2 of us (A.S. and C.A.) in a blinded fashion using the Rayyan software for meta-analyses (Qatar Computing Research Institute). The inclusion criteria were double-blind, placebo-controlled randomized clinical trials that used PDE5I for ED treatment or had ED as a comorbidity for another condition and that were reported in English. After unblinding with the Rayyan software, any discrepancies between the 2 reviewers were reconciled in a consensus meeting. The study selection procedure adhered to the Consolidated Standards of Reporting Trials (CONSORT) reporting guideline to ensure adequate quality of included studies. A flowchart of study selection is given in Figure 1.

    Statistical Analysis

    Data extraction was independently conducted by 2 of us (A.S. and M.P.). Studies were excluded from the meta-analysis if they did not contain any IIEF questionnaire data, did not report any separate data for drug and placebo arms, provided incomplete data, did not allow the calculation of an effect size, or used mixed treatments with proposed effects for ED in the treatment regimen (eg, testosterone). The quality of included studies was graded with Jadad scores16 and was included in the risk of bias assessments at the study and outcome levels.

    The Comprehensive Meta-Analysis software, version 3.0, was used for data management and statistical calculations of bias-corrected standardized mean differences (Hedges g). Effect size is commonly interpreted as small (Hedges g, 0.2), moderate (Hedges g, 0.5), or large (Hedges g, 0.8). Treatment response data from various domains of the IIEF questionnaire were analyzed separately per treatment arm as measured from before to after treatment, as well as the difference in outcomes between patients receiving active treatment and those receiving placebo. All analyses were performed with a random-effects approach using a 2-tailed α = . 05.

    Studies that contained arms with different doses of active drug treatment were averaged to a mean treatment response. In line with a prespecified protocol, subanalyses were performed to explain effect size heterogeneity. Moderators included mean age of participants, study duration, evidence of financial interest, study drug, Jadad scale (range of 0-5, with higher numbers indicating higher quality), and comorbidities. A random-effect metaregression analysis was conducted on mean age of study participants, study drug, study duration, and influence of financial interest by study sponsor or investigators.

    Results

    A total of 63 studies fulfilled the inclusion criteria; 59 studies were included in the main analysis that assessed the effect size before and after treatment for the various domains of IIEF. Four studies were analyzed separately because PDE5Is were used for treatment of ED after prostate cancer treatment and the design and patient groups differed considerably from the other studies (end of treatment scores indicate worsened erectile function compared with baseline because of surgery or radiotherapy). The treatment effect size in this subset of studies was calculated in a traditional drug vs placebo comparison. The methodologic quality of studies had a mean (SD) of 3.6 (0.88) points on the Jadad scale.16 A funnel plot was created in the Comprehensive Meta-Analysis software and revealed no risks of publication bias. The 63 included trials (Table 1) included a total of 12 564 men with ED (mean [SD] age, 55 [7] years; age range, 36-68 years). Some studies reported the cause of ED, but in general, studies represented a mix of peripheral and centrally mediated causes of ED, which was commonly referred to in the literature as organic and psychogenic. The mean duration of a treatment trial was 14 weeks (range, 4-104 weeks). A calculation on the combined effect size within the drug and placebo arms was conducted for all included studies in the main analysis (k = 59) excluding the 4 studies in patients with prostate surgery. The effect size in the placebo arm showed a small to moderate improvement of erectile function (Hedges g [SE], 0.35 [0.03]; I2 = 70.48; P < .001). The overall effect size in the drug arm showed a large response (Hedges g [SE], 1.25 [0.07]; I2 = 93.34; P < .001). A comparison between responses in the drug and placebo arms revealed a large difference in favor of active drug (Hedges g [SE], 1.04 [0.08]; I2 = 92.38; P < .001) (Figure 2).

    An analysis was performed on the other domains of the IIEF (ie, the IIEF-OF, IIEF-IS, IIEF-SD, and IIEF-OS). Not all included studies reported data on all domains; therefore, the number of studies per domain in this follow-up analysis was reduced. All results of IIEF subdomains are given in Table 2. For the effect size on orgasmic function (IIEF-OF; n = 31), the drug arm showed a high response, whereas the placebo arm showed a lower response, and between-group analysis showed a moderate response in favor of the drug arm. For intercourse satisfaction (IIEF-IS; n = 40), the drug arm showed a large response, the placebo arm showed a moderate response, and the between-group analysis showed a large effect size that favored the study drug. For sexual desire (IIEF-SD; n = 30), the drug arm showed a moderate response, and the placebo arm showed a low to moderate response. The between-group analysis was in favor of the study drug, with a moderate effect size. For overall satisfaction (IIEF-OS; n = 39), the drug arm showed a large response, whereas the placebo arm showed a low to moderate response. The between-group analysis showed a large effect size that favored the drug arm.

    The effect size for studies in which ED was associated with posttraumatic stress disorder (PTSD; n = 2) indicated a large response for the drug arm (Hedges g [SE], 1.12 [0.39]; I2 = 77.79; P = .004) and a large response in the placebo arm (Hedges g [SE], 0.77 [0.32]; I2 = 76.15; P = .02). The between-group analysis yielded a moderate effect size in favor of the study drug (Hedges g [SE], 0.40 [0.17]; I2 = 27.64; P = .02).

    Using a regression model, we assessed the association of moderators with ED treatment responses. In an overall analysis including data from the drug and placebo arms combined, no significant association of PDE5I drug type with treatment responses was found (q = 10.02; df = 6; I2 = 94.44; P = .12). The association was significant when the placebo arm was analyzed separately (q = 15.96; df = 6; I2 = 68.63; P = .01), but no significant association was seen in the drug arm (q = 11.14; df = 6; I2 = 92.83; P = .08) or in the between-group comparisons (q = 11.79; df = 6; I2 = 92.71; P = .07). There was a high correlation between treatment responses in the drug and placebo arm (r = 0.67), and without avanafil, a drug assessed in only 2 of the 63 studies, the correlation was higher (r = 0.94). There was no significant association of any of the other moderators with ED treatment responses (ie, financial interest, study duration, mean study participant age, or Jadad score). For these moderators, there were no significant associations for drug and placebo combined, for drug and placebo arms separately, or in a traditional drug vs placebo comparison.

    An explorative analysis was conducted on the studies using PDE5Is as aid in recovery of erectile function after prostate surgery or radiotherapy (n = 4). This between-group analysis of the effect size did not show a significant response in favor of drug vs placebo (Hedges g [SE], 0.29 [0.17]; I2 = 59.35; P = .08).

    Discussion

    This study found a significant association between placebo treatment and IIEF-EF scores in patients with ED, but the potential mechanisms are still unexplored. One possibility is that the association between placebo effect and erectile function are mediated by an increased nervous tone in the thoracolumbar tract because this nerve tract is mainly influenced by arousal mechanisms.3 Several neurobiological mechanisms have been proposed to underlie placebo effects. Endogenous opioids and cannabinoids have been proposed to mediate the placebo effect in various conditions.9-11 Given that these 2 substrates (opioid and cannabinoid) are mainly involved in a negative association with sexual arousal, it seems unlikely that they are associated with the placebo effect in treatment for ED. Another commonly proposed neural substrate for the placebo effect, the dopaminergic system,13 would be more likely to be involved in the association between placebo effect and erectile function because dopamine has a positive association with sexual arousal.80 The dopaminergic hypothesis is supported by dopamine agonists having been used in the treatment of ED.81-83

    There was a significant association of the active drug with erectile function scores in patients with ED. Given that the site of action of PDE5Is is the smooth muscle cells that influence the blood flow necessary to achieve erection, it seems plausible that the effect of the active drug would vary depending on the cause of the ED. If the problem were mainly vascular or endocrinologic, such as in atherosclerosis, diabetes, or hypogonadism, it seems plausible that the PDE5Is would have a strong effect because they address the underlying pathophysiological cause. If the nerves to the penis have been severed or severely damaged (as in the 4 prostate cancer trials in this analysis), the PDE5Is cannot amplify the nervous signal to the smooth muscle cells; thus, PDE5Is would have no specific effect.

    Other domains of the IIEF questionnaire showed variations in effect sizes, in which responses in the drug arm were lower for orgasmic function (IIEF-OF) and sexual desire (IIEF-SD) compared with erectile function (IIEF-EF). This finding was expected because orgasmic function and especially sexual desire are associated with numerous factors other than the ability to achieve erection. There were also variations in effect size in the placebo arm, in which the response was lower for IIEF-OF and IIEF-SD compared with IIEF-EF. This finding was most likely attributable to the same factors as the differences among domains in the drug arm. Of interest, the response for intercourse satisfaction (IIEF-IS) was higher compared with the IIEF-EF response in the placebo arm. This result was not concordant with the result in the drug arm, and because the degree of the association with intercourse satisfaction may be more affected by psychological factors, this result supports separate mechanisms for placebo and drug improvements in patients with ED.

    The 2 studies52,64 on treatment for PTSD-associated ED had a lower effect size for the drug response compared with results from the main analysis. The effect size of the placebo response in PTSD studies was markedly higher compared with the main analysis. Assuming that ED in this patient group was associated with psychological stress caused by traumatic experiences, the large improvement in the placebo arm could indicate that psychological factors might be associated with ED symptom improvements. This finding is supported by clinical studies84,85 that found comparable ED improvements for psychological interventions and PDE5Is, or increased improvements when combined (compared with PDE5Is alone).86 However, neither the drug nor placebo arm in the 2 studies52,64 on ED associated with PTSD reached a median IIEF-EF score, indicating normal erectile function, although clinically significant improvements were observed.

    A metaregression analysis revealed a significant association between PDE5I drug type and treatment responses in the placebo arm and high correlation between the treatment response in the drug and placebo arms. The association of PDE5I drug type with erectile function in individuals given placebo suggests that differences in subjective perception of the different drugs exist because they differ in brand names, marketing, and visual appearance. Previous research shows that placebo effects are associated with labels87 and marketing,88 and it is possible that such differences contributed to the results in the present study.

    No significant association of study duration, participant age, Jadad score, or financial interest with treatment effect size was found in the drug or placebo arm. Study duration is difficult to compare with previous studies of placebo longevity because PDE5Is are taken when needed, and the effects may be different from placebo responses in long-term use of, for example, antidepressants.89 Furthermore, there was little variation in participant age among studies, and new studies are needed to determine whether placebo responses in ED treatment may differ depending on participant age. The lack of an association between documented financial interests and treatment responses suggests that the trials included in this meta-analysis were not biased by the potential influence of a study sponsor.

    The Jadad score reflects the quality of the clinical trials included in the meta-analysis. The lack of an association between Jadad scores and treatment outcomes indicates that the results in this meta-analysis are not biased by study quality.

    Usually, PDE5Is are only taken before sexual intercourse. It has been theorized that daily long-term treatment with PDE5Is after prostate surgery and radiotherapy can aid the healing of damaged nerves through an amplification of the nervous input to the smooth muscles of the cavernous body.90 Previous research4 regarding the usefulness of this practice has been inconclusive. The results from the present meta-analysis showed no statistically significant differences between the response in the drug and placebo arms among patients who underwent treatment for prostate cancer. Individual studies91,92 that are not part of this meta-analysis have found stronger associations of erectile function and active drug compared with placebo. However, differences in the degree of nerve damage in the pelvic area may represent a confounding factor by which patients with less severe nerve damage after surgery or radiotherapy might receive a short-term benefit from PDE5Is (unrelated to the proposed effects of long-term treatment). The results in this meta-analysis suggest that PDE5Is have no significant association with the recovery of erectile function after prostate surgery or radiotherapy. Until robust differences between drug and placebo have been demonstrated, the practice of prescribing daily intake of PDE5Is after prostate cancer treatment may not be considered evidence, questioning the long-term use of PDE5Is for these patients.

    Limitations

    This study has limitations. This meta-analysis is limited by the inability to compare improvements in the placebo arm with no-treatment data from the included study populations. In any placebo-controlled drug trial, the inclusion of a no-treatment group will help understanding of how much of the treatment response is attributable to the drug itself, how much is attributable to the placebo effect, and how much of the treatment response is attributable to factors such as spontaneous remission and regression to the mean. We cannot exclude that the observed placebo response was partly associated with spontaneous ED improvements. The inclusion of a no-treatment control group in randomized clinical trials of ED is warranted because it would potentially lead to a better understanding of placebo effects in PDE5I treatment trials.

    Conclusions

    This systematic review and meta-analysis found a significant association of placebo and ED outcomes, with larger effect sizes among men with PTSD-associated ED. No difference in erectile function was found between those who received placebo vs PDE5I for ED after prostate surgery.

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    Article Information

    Accepted for Publication: January 30, 2020.

    Published: March 20, 2020. doi:10.1001/jamanetworkopen.2020.1423

    Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2020 Stridh A et al. JAMA Network Open.

    Corresponding Author: Alexander Stridh, MSc, Department of Clinical Neuroscience, Karolinska Institute, Nobels väg 9, 17177 Stockholm, Sweden (alexander.stridh@stud.ki.se).

    Author Contributions: Drs Abé and Jensen contributed equally to this work. Mr Stridh and Dr Jensen had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

    Concept and design: Stridh, Kirsch, Abé, Jensen.

    Acquisition, analysis, or interpretation of data: Stridh, Pontén, Arver, Abé, Jensen.

    Drafting of the manuscript: Stridh, Jensen.

    Critical revision of the manuscript for important intellectual content: All authors.

    Statistical analysis: Stridh, Pontén, Kirsch, Abé, Jensen.

    Administrative, technical, or material support: Stridh, Arver, Abé, Jensen.

    Supervision: Arver, Kirsch, Abé, Jensen.

    Conflict of Interest Disclosures: None reported.

    Funding/Support: This study supported by the Pro Futura Grant from Riksbankens Jubileumsfond (Dr Jensen).

    Role of the Funder/Sponsor: The funding source had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

    Additional Contributions: Magdalena Svanberg, MA, and Carl Gornitzki, MLIS, librarians at the Karolinska University Library, Solna, Sweden, assisted in the search for articles in this meta-analysis. They were not compensated for their work.

    References
    1.
    Goldstein  I, Burnett  AL, Rosen  RC, Park  PW, Stecher  VJ.  The serendipitous story of sildenafil: an unexpected oral therapy for erectile dysfunction.  Sex Med Rev. 2019;7(1):115-128. doi:10.1016/j.sxmr.2018.06.005PubMedGoogle ScholarCrossref
    2.
    Delate  T, Simmons  VA, Motheral  BR.  Patterns of use of sildenafil among commercially insured adults in the United States: 1998-2002.  Int J Impot Res. 2004;16(4):313-318. doi:10.1038/sj.ijir.3901191PubMedGoogle ScholarCrossref
    3.
    Dean  RC, Lue  TF.  Physiology of penile erection and pathophysiology of erectile dysfunction.  Urol Clin North Am. 2005;32(4):379-395, v. v. doi:10.1016/j.ucl.2005.08.007PubMedGoogle ScholarCrossref
    4.
    Yafi  FA, Jenkins  L, Albersen  M,  et al.  Erectile dysfunction.  Nat Rev Dis Primers. 2016;2:16003. doi:10.1038/nrdp.2016.3PubMedGoogle ScholarCrossref
    5.
    Rosen  RC, Riley  A, Wagner  G, Osterloh  IH, Kirkpatrick  J, Mishra  A.  The international index of erectile function (IIEF): a multidimensional scale for assessment of erectile dysfunction.  Urology. 1997;49(6):822-830. doi:10.1016/S0090-4295(97)00238-0PubMedGoogle ScholarCrossref
    6.
    Pastuszak  AW.  Current diagnosis and management of erectile dysfunction.  Curr Sex Health Rep. 2014;6(3):164-176. doi:10.1007/s11930-014-0023-9PubMedGoogle ScholarCrossref
    7.
    Corona  G, Lee  DM, Forti  G,  et al; EMAS Study Group.  Age-related changes in general and sexual health in middle-aged and older men: results from the European Male Ageing Study (EMAS).  J Sex Med. 2010;7(4, pt 1):1362-1380. doi:10.1111/j.1743-6109.2009.01601.xPubMedGoogle ScholarCrossref
    8.
    Benedetti  F, Carlino  E, Pollo  A.  How placebos change the patient’s brain.  Neuropsychopharmacology. 2011;36(1):339-354. doi:10.1038/npp.2010.81PubMedGoogle ScholarCrossref
    9.
    Sauro  MD, Greenberg  RP.  Endogenous opiates and the placebo effect: a meta-analytic review.  J Psychosom Res. 2005;58(2):115-120. doi:10.1016/j.jpsychores.2004.07.001PubMedGoogle ScholarCrossref
    10.
    Amanzio  M, Benedetti  F.  Neuropharmacological dissection of placebo analgesia: expectation-activated opioid systems versus conditioning-activated specific subsystems.  J Neurosci. 1999;19(1):484-494. doi:10.1523/JNEUROSCI.19-01-00484.1999PubMedGoogle ScholarCrossref
    11.
    Benedetti  F, Amanzio  M, Rosato  R, Blanchard  C.  Nonopioid placebo analgesia is mediated by CB1 cannabinoid receptors.  Nat Med. 2011;17(10):1228-1230. doi:10.1038/nm.2435PubMedGoogle ScholarCrossref
    12.
    de la Fuente-Fernández  R, Lidstone  S, Stoessl  AJ.  Placebo effect and dopamine release.  J Neural Transm Suppl. 2006;(70):415-418.PubMedGoogle Scholar
    13.
    de la Fuente-Fernández  R.  The placebo-reward hypothesis: dopamine and the placebo effect.  Parkinsonism Relat Disord. 2009;15(suppl 3):S72-S74. doi:10.1016/S1353-8020(09)70785-0PubMedGoogle ScholarCrossref
    14.
    Wager  TD, Rilling  JK, Smith  EE,  et al.  Placebo-induced changes in FMRI in the anticipation and experience of pain.  Science. 2004;303(5661):1162-1167. doi:10.1126/science.1093065PubMedGoogle ScholarCrossref
    15.
    Geuter  S, Eippert  F, Hindi Attar  C, Büchel  C.  Cortical and subcortical responses to high and low effective placebo treatments.  Neuroimage. 2013;67:227-236. doi:10.1016/j.neuroimage.2012.11.029PubMedGoogle ScholarCrossref
    16.
    Jadad  AR, Moore  RA, Carroll  D,  et al.  Assessing the quality of reports of randomized clinical trials: is blinding necessary?  Control Clin Trials. 1996;17(1):1-12. doi:10.1016/0197-2456(95)00134-4PubMedGoogle ScholarCrossref
    17.
    Albuquerque  DC, Miziara  LJ, Saraiva  JF, Rodrigues  US, Ribeiro  AB, Wajngarten  M.  Efficacy, safety and tolerability of sildenafil in Brazilian hypertensive patients on multiple antihypertensive drugs.  Int Braz J Urol. 2005;31(4):342-353. doi:10.1590/S1677-55382005000400008PubMedGoogle ScholarCrossref
    18.
    Althof  SE, O’leary  MP, Cappelleri  JC,  et al; International SEAR Study Group.  Sildenafil citrate improves self-esteem, confidence, and relationships in men with erectile dysfunction: results from an international, multi-center, double-blind, placebo-controlled trial.  J Sex Med. 2006;3(3):521-529. doi:10.1111/j.1743-6109.2006.00234.xPubMedGoogle ScholarCrossref
    19.
    Bénard  F, Carrier  S, Lee  JC, Talwar  V, Defoy  I.  Men with mild erectile dysfunction benefit from sildenafil treatment.  J Sex Med. 2010;7(11):3725-3735. doi:10.1111/j.1743-6109.2010.02015.xPubMedGoogle ScholarCrossref
    20.
    Carrier  S, Brock  GB, Pommerville  PJ,  et al.  Efficacy and safety of oral tadalafil in the treatment of men in Canada with erectile dysfunction: a randomized, double-blind, parallel, placebo-controlled clinical trial.  J Sex Med. 2005;2(5):685-698. doi:10.1111/j.1743-6109.2005.00097.xPubMedGoogle ScholarCrossref
    21.
    Chen  KK, Jiann  BP, Lin  JS,  et al.  Efficacy and safety of on-demand oral tadalafil in the treatment of men with erectile dysfunction in Taiwan: a randomized, double-blind, parallel, placebo-controlled clinical study.  J Sex Med. 2004;1(2):201-208. doi:10.1111/j.1743-6109.2004.04029.xPubMedGoogle ScholarCrossref
    22.
    Chung  JH, Kang  DH, Oh  CY,  et al.  Safety and efficacy of once daily administration of 50 mg mirodenafil in patients with erectile dysfunction: a multicenter, double-blind, placebo controlled trial.  J Urol. 2013;189(3):1006-1013. doi:10.1016/j.juro.2012.08.243PubMedGoogle Scholar
    23.
    Eardley  I, Gentile  V, Austoni  E,  et al.  Efficacy and safety of tadalafil in a Western European population of men with erectile dysfunction.  BJU Int. 2004;94(6):871-877. doi:10.1111/j.1464-410X.2004.05049.xPubMedGoogle Scholar
    24.
    Egerdie  RB, Auerbach  S, Roehrborn  CG,  et al.  Tadalafil 2.5 or 5 mg administered once daily for 12 weeks in men with both erectile dysfunction and signs and symptoms of benign prostatic hyperplasia: results of a randomized, placebo-controlled, double-blind study.  J Sex Med. 2012;9(1):271-281. doi:10.1111/j.1743-6109.2011.02504.xPubMedGoogle Scholar
    25.
    Evliyaoğlu  Y, Yelsel  K, Kobaner  M, Alma  E, Saygılı  M.  Efficacy and tolerability of tadalafil for treatment of erectile dysfunction in men taking serotonin reuptake inhibitors.  Urology. 2011;77(5):1137-1141. doi:10.1016/j.urology.2010.12.036PubMedGoogle Scholar
    26.
    Zonana Farca  E, Francolugo-Vélez  V, Moy-Eransus  C, Orozco Bravo  A, Tseng  LJ, Stecher  VJ.  Self-esteem, confidence and relationship satisfaction in men with erectile dysfunction: a randomized, parallel-group, double-blind, placebo-controlled study of sildenafil in Mexico.  Int J Impot Res. 2008;20(4):402-408. doi:10.1038/ijir.2008.24PubMedGoogle Scholar
    27.
    Fawzi  A, Kamel  M, Salem  E,  et al.  Sildenafil citrate in combination with tamsulosin versus tamsulosin monotherapy for management of male lower urinary tract symptoms due to benign prostatic hyperplasia: a randomised, double-blind, placebo-controlled trial.  Arab J Urol. 2016;15(1):53-59. doi:10.1016/j.aju.2016.11.001PubMedGoogle Scholar
    28.
    Gacci  M, Vittori  G, Tosi  N,  et al.  A randomized, placebo-controlled study to assess safety and efficacy of vardenafil 10 mg and tamsulosin 0.4 mg vs. tamsulosin 0.4 mg alone in the treatment of lower urinary tract symptoms secondary to benign prostatic hyperplasia.  J Sex Med. 2012;9(6):1624-1633. doi:10.1111/j.1743-6109.2012.02718.xPubMedGoogle Scholar
    29.
    Gittelman  M, McMahon  CG, Rodríguez-Rivera  JA, Beneke  M, Ulbrich  E, Ewald  S.  The POTENT II randomised trial: efficacy and safety of an orodispersible vardenafil formulation for the treatment of erectile dysfunction.  Int J Clin Pract. 2010;64(5):594-603. doi:10.1111/j.1742-1241.2010.02358.xPubMedGoogle Scholar
    30.
    Giuliano  F, Oelke  M, Jungwirth  A,  et al.  Tadalafil once daily improves ejaculatory function, erectile function, and sexual satisfaction in men with lower urinary tract symptoms suggestive of benign prostatic hyperplasia and erectile dysfunction: results from a randomized, placebo- and tamsulosin-controlled, 12-week double-blind study.  J Sex Med. 2013;10(3):857-865. doi:10.1111/jsm.12039PubMedGoogle Scholar
    31.
    Glina  S, Damião  R, Abdo  C, Afif-Abdo  J, Tseng  LJ, Stecher  V.  Self-esteem, confidence, and relationships in Brazilian men with erectile dysfunction receiving sildenafil citrate: a randomized, parallel-group, double-blind, placebo-controlled study in Brazil.  J Sex Med. 2009;6(1):268-275. doi:10.1111/j.1743-6109.2008.01026.xPubMedGoogle Scholar
    32.
    Glina  S, Toscano  I, Gomatzky  C,  et al.  Efficacy and tolerability of lodenafil carbonate for oral therapy in erectile dysfunction: a phase II clinical trial.  J Sex Med. 2009;6(2):553-557. doi:10.1111/j.1743-6109.2008.01079.xPubMedGoogle Scholar
    33.
    Glina  S, Fonseca  GN, Bertero  EB,  et al.  Efficacy and tolerability of lodenafil carbonate for oral therapy of erectile dysfunction: a phase III clinical trial.  J Sex Med. 2010;7(5):1928-1936. doi:10.1111/j.1743-6109.2010.01711.xPubMedGoogle Scholar
    34.
    Heiman  JR, Talley  DR, Bailen  JL,  et al.  Sexual function and satisfaction in heterosexual couples when men are administered sildenafil citrate (Viagra) for erectile dysfunction: a multicentre, randomised, double-blind, placebo-controlled trial.  BJOG. 2007;114(4):437-447. doi:10.1111/j.1471-0528.2006.01228.xPubMedGoogle Scholar
    35.
    Hellstrom  WJ, Kaminetsky  J, Belkoff  LH,  et al.  Efficacy of avanafil 15 minutes after dosing in men with erectile dysfunction: a randomized, double-blind, placebo controlled study.  J Urol. 2015;194(2):485-492. doi:10.1016/j.juro.2014.12.101PubMedGoogle Scholar
    36.
    Jones  LA, Klimberg  IW, McMurray  JG, Padula  R, Tseng  LJ, Stecher  VJ.  Effect of sildenafil citrate on the male sexual experience assessed with the Sexual Experience Questionnaire: a multicenter, double-blind, placebo-controlled trial with open-label extension.  J Sex Med. 2008;5(8):1955-1964. doi:10.1111/j.1743-6109.2008.00879.xPubMedGoogle Scholar
    37.
    Kadioglu  A, Grohmann  W, Depko  A, Levinson  IP, Sun  F, Collins  S.  Quality of erections in men treated with flexible-dose sildenafil for erectile dysfunction: multicenter trial with a double-blind, randomized, placebo-controlled phase and an open-label phase.  J Sex Med. 2008;5(3):726-734. doi:10.1111/j.1743-6109.2007.00701.xPubMedGoogle Scholar
    38.
    Kim  ED, Seftel  AD, Goldfischer  ER, Ni  X, Burns  PR.  A return to normal erectile function with tadalafil once daily after an incomplete response to as-needed PDE5 inhibitor therapy.  J Sex Med. 2014;11(3):820-830. doi:10.1111/jsm.12253PubMedGoogle Scholar
    39.
    Mahon  A, Sidhu  PS, Muir  G, Macdougall  IC.  The efficacy of sildenafil for the treatment of erectile dysfunction in male peritoneal dialysis patients.  Am J Kidney Dis. 2005;45(2):381-387. doi:10.1053/j.ajkd.2004.10.012PubMedGoogle Scholar
    40.
    Martin-Morales  A, Meijide  F, García  N, Artes  M, Muñoz  A.  Efficacy of vardenafil and influence on self-esteem and self-confidence in patients with severe erectile dysfunction.  J Sex Med. 2007;4(2):440-447. doi:10.1111/j.1743-6109.2006.00426.xPubMedGoogle Scholar
    41.
    Pattanaik  S, Kaundal  P, Mavuduru  RS, Singh  SK, Mandal  AK.  Endothelial dysfunction in patients with erectile dysfunction: a double-blind, randomized-control trial using tadalafil.  Sex Med. 2019;7(1):41-47. doi:10.1016/j.esxm.2018.11.008PubMedGoogle Scholar
    42.
    McCullough  AR, Steidle  CP, Klee  B, Tseng  LJ.  Randomized, double-blind, crossover trial of sildenafil in men with mild to moderate erectile dysfunction: efficacy at 8 and 12 hours postdose.  Urology. 2008;71(4):686-692. doi:10.1016/j.urology.2007.12.025PubMedGoogle Scholar
    43.
    McMahon  CG, Stuckey  BG, Lording  DW,  et al.  A 6-month study of the efficacy and safety of tadalafil in the treatment of erectile dysfunction: a randomised, double-blind, parallel-group, placebo-controlled study in Australian men.  Int J Clin Pract. 2005;59(2):143-149. doi:10.1111/j.1742-1241.2005.00451.xPubMedGoogle Scholar
    44.
    McVary  KT, Roehrborn  CG, Kaminetsky  JC,  et al.  Tadalafil relieves lower urinary tract symptoms secondary to benign prostatic hyperplasia.  J Urol. 2007;177(4):1401-1407. doi:10.1016/j.juro.2006.11.037PubMedGoogle Scholar
    45.
    McVary  KT, Monnig  W, Camps  JL  Jr, Young  JM, Tseng  LJ, van den Ende  G.  Sildenafil citrate improves erectile function and urinary symptoms in men with erectile dysfunction and lower urinary tract symptoms associated with benign prostatic hyperplasia: a randomized, double-blind trial.  J Urol. 2007;177(3):1071-1077. doi:10.1016/j.juro.2006.10.055PubMedGoogle Scholar
    46.
    Meuleman  E, Cuzin  B, Opsomer  RJ,  et al.  A dose-escalation study to assess the efficacy and safety of sildenafil citrate in men with erectile dysfunction.  BJU Int. 2001;87(1):75-81. doi:10.1046/j.1464-410x.2001.00998.xPubMedGoogle Scholar
    47.
    Miner  M, Gilderman  L, Bailen  J,  et al.  Vardenafil in men with stable statin therapy and dyslipidemia.  J Sex Med. 2008;5(6):1455-1467. doi:10.1111/j.1743-6109.2008.00820.xPubMedGoogle Scholar
    48.
    Moncada  I, Martínez-Jabaloyas  JM, Rodriguez-Vela  L,  et al.  Emotional changes in men treated with sildenafil citrate for erectile dysfunction: a double-blind, placebo-controlled clinical trial.  J Sex Med. 2009;6(12):3469-3477. doi:10.1111/j.1743-6109.2009.01514.xPubMedGoogle Scholar
    49.
    Moon  KH, Ko  YH, Kim  SW,  et al.  Efficacy of once-daily administration of udenafil for 24 weeks on erectile dysfunction: results from a randomized multicenter placebo-controlled clinical trial.  J Sex Med. 2015;12(5):1194-1201. doi:10.1111/jsm.12862PubMedGoogle Scholar
    50.
    Nunes  LV, Lacaz  FS, Bressan  RA, Nunes  SO, Mari  JdeJ.  Adjunctive treatment with lodenafil carbonate for erectile dysfunction in outpatients with schizophrenia and spectrum: a randomized, double-blind, crossover, placebo-controlled trial.  J Sex Med. 2013;10(4):1136-1145. doi:10.1111/jsm.12040PubMedGoogle Scholar
    51.
    Nurnberg  HG, Hensley  PL, Gelenberg  AJ, Fava  M, Lauriello  J, Paine  S.  Treatment of antidepressant-associated sexual dysfunction with sildenafil: a randomized controlled trial.  JAMA. 2003;289(1):56-64. doi:10.1001/jama.289.1.56PubMedGoogle Scholar
    52.
    Orr  G, Weiser  M, Polliack  M, Raviv  G, Tadmor  D, Grunhaus  L.  Effectiveness of sildenafil in treating erectile dysfunction in PTSD patients: a double-blind, placebo-controlled crossover study.  J Clin Psychopharmacol. 2006;26(4):426-430. doi:10.1097/01.jcp.0000227701.33999.b3PubMedGoogle Scholar
    53.
    Ortaç  M, Çayan  S, Çalişkan  MK,  et al.  Efficacy and tolerability of udenafil in Turkish men with erectile dysfunction of psychogenic and organic aetiology: a randomized, double-blind, placebo-controlled study.  Andrology. 2013;1(4):549-555. doi:10.1111/j.2047-2927.2013.00085.xPubMedGoogle Scholar
    54.
    Paick  JS, Kim  SW, Yang  DY,  et al.  The efficacy and safety of udenafil, a new selective phosphodiesterase type 5 inhibitor, in patients with erectile dysfunction.  J Sex Med. 2008;5(4):946-953. doi:10.1111/j.1743-6109.2007.00723.xPubMedGoogle Scholar
    55.
    Paick  JS, Ahn  TY, Choi  HK,  et al.  Efficacy and safety of mirodenafil, a new oral phosphodiesterase type 5 inhibitor, for treatment of erectile dysfunction.  J Sex Med. 2008;5(11):2672-2680. doi:10.1111/j.1743-6109.2008.00945.xPubMedGoogle Scholar
    56.
    Paick  JS, Kim  JJ, Kim  SC,  et al.  Efficacy and safety of mirodenafil in men taking antihypertensive medications.  J Sex Med. 2010;7(9):3143-3152. doi:10.1111/j.1743-6109.2010.01926.xPubMedGoogle Scholar
    57.
    Park  HJ, Park  JK, Park  K, Min  K, Park  NC.  Efficacy of udenafil for the treatment of erectile dysfunction up to 12 hours after dosing: a randomized placebo-controlled trial.  J Sex Med. 2010;7(6):2209-2216. doi:10.1111/j.1743-6109.2010.01817.xPubMedGoogle Scholar
    58.
    Park  HJ, Choi  HK, Ahn  TY,  et al.  Efficacy and safety of oral mirodenafil in the treatment of erectile dysfunction in diabetic men in Korea: a multicenter, randomized, double-blind, placebo-controlled clinical trial.  J Sex Med. 2010;7(8):2842-2850. doi:10.1111/j.1743-6109.2010.01888.xPubMedGoogle Scholar
    59.
    Park  SY, Choi  GS, Park  JS, Kim  HJ, Park  JA, Choi  JI.  Efficacy and safety of udenafil for the treatment of erectile dysfunction after total mesorectal excision of rectal cancer: a randomized, double-blind, placebo-controlled trial.  Surgery. 2015;157(1):64-71. doi:10.1016/j.surg.2014.07.007PubMedGoogle Scholar
    60.
    Park  HJ, Kim  SW, Kim  JJ,  et al.  A randomized, placebo-controlled, double-blind, multi-center therapeutic confirmatory study to evaluate the safety and efficacy of avanafil in Korean patients with erectile dysfunction.  J Korean Med Sci. 2017;32(6):1016-1023. doi:10.3346/jkms.2017.32.6.1016PubMedGoogle Scholar
    61.
    Porst  H, Rosen  R, Padma-Nathan  H,  et al.  The efficacy and tolerability of vardenafil, a new, oral, selective phosphodiesterase type 5 inhibitor, in patients with erectile dysfunction: the first at-home clinical trial.  Int J Impot Res. 2001;13(4):192-199. doi:10.1038/sj.ijir.3900713PubMedGoogle Scholar
    62.
    Porst  H, Kim  ED, Casabé  AR,  et al; LVHJ study team.  Efficacy and safety of tadalafil once daily in the treatment of men with lower urinary tract symptoms suggestive of benign prostatic hyperplasia: results of an international randomized, double-blind, placebo-controlled trial.  Eur Urol. 2011;60(5):1105-1113. doi:10.1016/j.eururo.2011.08.005PubMedGoogle Scholar
    63.
    Rosen  RC, Wincze  J, Mollen  MD, Gondek  K, McLeod  LD, Fisher  WA.  Responsiveness and minimum important differences for the erection quality scale.  J Urol. 2007;178(5):2076-2081. doi:10.1016/j.juro.2007.07.019PubMedGoogle Scholar
    64.
    Safarinejad  MR, Kolahi  AA, Ghaedi  G.  Safety and efficacy of sildenafil citrate in treating erectile dysfunction in patients with combat-related post-traumatic stress disorder: a double-blind, randomized and placebo-controlled study.  BJU Int. 2009;104(3):376-383. doi:10.1111/j.1464-410X.2009.08560.xPubMedGoogle Scholar
    65.
    Santi  D, Granata  AR, Guidi  A,  et al.  Six months of daily treatment with vardenafil improves parameters of endothelial inflammation and of hypogonadism in male patients with type 2 diabetes and erectile dysfunction: a randomized, double-blind, prospective trial.  Eur J Endocrinol. 2016;174(4):513-522. doi:10.1530/EJE-15-1100PubMedGoogle Scholar
    66.
    Saylan  M, Khalaf  I, Kadioglu  A,  et al.  Efficacy of tadalafil in Egyptian and Turkish men with erectile dysfunction.  Int J Clin Pract. 2006;60(7):812-819. doi:10.1111/j.1742-1241.2006.00993.xPubMedGoogle Scholar
    67.
    Seftel  AD, Wilson  SK, Knapp  PM, Shin  J, Wang  WC, Ahuja  S.  The efficacy and safety of tadalafil in United States and Puerto Rican men with erectile dysfunction.  J Urol. 2004;172(2):652-657. doi:10.1097/01.ju.0000132857.39680.cePubMedGoogle Scholar
    68.
    Seibel  I, Poli De Figueiredo  CE, Telöken  C, Moraes  JF.  Efficacy of oral sildenafil in hemodialysis patients with erectile dysfunction.  J Am Soc Nephrol. 2002;13(11):2770-2775. doi:10.1097/01.ASN.0000034201.97937.3EPubMedGoogle Scholar
    69.
    Seidman  SN, Roose  SP, Menza  MA, Shabsigh  R, Rosen  RC.  Treatment of erectile dysfunction in men with depressive symptoms: results of a placebo-controlled trial with sildenafil citrate.  Am J Psychiatry. 2001;158(10):1623-1630. doi:10.1176/appi.ajp.158.10.1623PubMedGoogle Scholar
    70.
    Shabsigh  R, Kaufman  J, Magee  M, Creanga  D, Russell  D, Budhwani  M.  A multicenter, double-blind, placebo-controlled trial to assess the efficacy of sildenafil citrate in men with unrecognized erectile dysfunction.  Urology. 2010;76(2):373-379. doi:10.1016/j.urology.2010.03.017PubMedGoogle Scholar
    71.
    Sharma  RK, Prasad  N, Gupta  A, Kapoor  R.  Treatment of erectile dysfunction with sildenafil citrate in renal allograft recipients: a randomized, double-blind, placebo-controlled, crossover trial.  Am J Kidney Dis. 2006;48(1):128-133. doi:10.1053/j.ajkd.2006.04.061PubMedGoogle Scholar
    72.
    Shim  YS, Pae  CU, Cho  KJ, Kim  SW, Kim  JC, Koh  JS.  Effects of daily low-dose treatment with phosphodiesterase type 5 inhibitor on cognition, depression, somatization and erectile function in patients with erectile dysfunction: a double-blind, placebo-controlled study.  Int J Impot Res. 2014;26(2):76-80. doi:10.1038/ijir.2013.38PubMedGoogle Scholar
    73.
    Skoumal  R, Chen  J, Kula  K,  et al.  Efficacy and treatment satisfaction with on-demand tadalafil (Cialis) in men with erectile dysfunction.  Eur Urol. 2004;46(3):362-369. doi:10.1016/j.eururo.2004.04.026PubMedGoogle Scholar
    74.
    Vardi  Y, Appel  B, Ofer  Y, Greunwald  I, Dayan  L, Jacob  G.  Effect of chronic sildenafil treatment on penile endothelial function: a randomized, double-blind, placebo controlled study.  J Urol. 2009;182(6):2850-2855. doi:10.1016/j.juro.2009.08.025PubMedGoogle Scholar
    75.
    Ziegler  D, Merfort  F, Van Ahlen  H, Yassin  A, Reblin  T, Neureither  M.  Efficacy and safety of flexible-dose vardenafil in men with type 1 diabetes and erectile dysfunction.  J Sex Med. 2006;3(5):883-891. doi:10.1111/j.1743-6109.2006.00295.xPubMedGoogle Scholar
    76.
    Zelefsky  MJ, Shasha  D, Branco  RD,  et al.  Prophylactic sildenafil citrate improves select aspects of sexual function in men treated with radiotherapy for prostate cancer.  J Urol. 2014;192(3):868-874. doi:10.1016/j.juro.2014.02.097PubMedGoogle Scholar
    77.
    Incrocci  L, Koper  PC, Hop  WC, Slob  AK.  Sildenafil citrate (Viagra) and erectile dysfunction following external beam radiotherapy for prostate cancer: a randomized, double-blind, placebo-controlled, cross-over study.  Int J Radiat Oncol Biol Phys. 2001;51(5):1190-1195. doi:10.1016/S0360-3016(01)01767-9PubMedGoogle Scholar
    78.
    Padma-Nathan  H, McCullough  AR, Levine  LA,  et al; Study Group.  Randomized, double-blind, placebo-controlled study of postoperative nightly sildenafil citrate for the prevention of erectile dysfunction after bilateral nerve-sparing radical prostatectomy.  Int J Impot Res. 2008;20(5):479-486. doi:10.1038/ijir.2008.33PubMedGoogle Scholar
    79.
    Pisansky  TM, Pugh  SL, Greenberg  RE,  et al.  Tadalafil for prevention of erectile dysfunction after radiotherapy for prostate cancer: the Radiation Therapy Oncology Group [0831] randomized clinical trial.  JAMA. 2014;311(13):1300-1307. doi:10.1001/jama.2014.2626PubMedGoogle Scholar
    80.
    Pfaus  JG.  Pathways of sexual desire.  J Sex Med. 2009;6(6):1506-1533. doi:10.1111/j.1743-6109.2009.01309.xPubMedGoogle Scholar
    81.
    Montorsi  F, Perani  D, Anchisi  D,  et al.  Brain activation patterns during video sexual stimulation following the administration of apomorphine: results of a placebo-controlled study.  Eur Urol. 2003;43(4):405-411. doi:10.1016/S0302-2838(03)00053-8PubMedGoogle Scholar
    82.
    Mulhall  JP.  Sublingual apomorphine for the treatment of erectile dysfunction.  Expert Opin Investig Drugs. 2002;11(2):295-302. doi:10.1517/13543784.11.2.295PubMedGoogle Scholar
    83.
    Montorsi  F, Perani  D, Anchisi  D,  et al.  Apomorphine-induced brain modulation during sexual stimulation: a new look at central phenomena related to erectile dysfunction.  Int J Impot Res. 2003;15(3):203-209. doi:10.1038/sj.ijir.3900999PubMedGoogle Scholar
    84.
    Melnik  T, Abdo  CH.  Psychogenic erectile dysfunction: comparative study of three therapeutic approaches.  J Sex Marital Ther. 2005;31(3):243-255. doi:10.1080/00926230590513465PubMedGoogle Scholar
    85.
    McCabe  MP, Price  E, Piterman  L, Lording  D.  Evaluation of an internet-based psychological intervention for the treatment of erectile dysfunction.  Int J Impot Res. 2008;20(3):324-330. doi:10.1038/ijir.2008.3PubMedGoogle Scholar
    86.
    Aubin  S, Heiman  JR, Berger  RE, Murallo  AV, Yung-Wen  L.  Comparing sildenafil alone vs. sildenafil plus brief couple sex therapy on erectile dysfunction and couples’ sexual and marital quality of life: a pilot study.  J Sex Marital Ther. 2009;35(2):122-143. doi:10.1080/00926230802712319PubMedGoogle Scholar
    87.
    Kam-Hansen  S, Jakubowski  M, Kelley  JM,  et al.  Altered placebo and drug labeling changes the outcome of episodic migraine attacks.  Sci Transl Med. 2014;6(218):218ra5. doi:10.1126/scitranslmed.3006175PubMedGoogle Scholar
    88.
    Waber  RL, Shiv  B, Carmon  Z, Ariely  D.  Commercial features of placebo and therapeutic efficacy.  JAMA. 2008;299(9):1016-1017. doi:10.1001/jama.299.9.1016PubMedGoogle Scholar
    89.
    Khan  A, Redding  N, Brown  WA.  The persistence of the placebo response in antidepressant clinical trials.  J Psychiatr Res. 2008;42(10):791-796. doi:10.1016/j.jpsychires.2007.10.004PubMedGoogle Scholar
    90.
    Schwartz  EJ, Wong  P, Graydon  RJ.  Sildenafil preserves intracorporeal smooth muscle after radical retropubic prostatectomy.  J Urol. 2004;171(2, pt 1):771-774. doi:10.1097/01.ju.0000106970.97082.61PubMedGoogle Scholar
    91.
    Raina  R, Lakin  MM, Agarwal  A,  et al.  Long-term effect of sildenafil citrate on erectile dysfunction after radical prostatectomy: 3-year follow-up.  Urology. 2003;62(1):110-115. doi:10.1016/S0090-4295(03)00157-2PubMedGoogle Scholar
    92.
    Ohebshalom  M, Parker  M, Guhring  P, Mulhall  JP.  The efficacy of sildenafil citrate following radiation therapy for prostate cancer: temporal considerations.  J Urol. 2005;174(1):258-262. doi:10.1097/01.ju.0000164286.47518.1ePubMedGoogle Scholar
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