Sildenafil citrate (Viagra, Pfizer Pharmaceuticals, New York, NY) has been approved for marketing by the FDA as therapy for erectile dysfunction. The drug is a selective inhibitor of phosphodiesterase 5 and acts to enhance the effects of nitric oxide, causing smooth muscle relaxation and inflow of blood to the corpus cavernosum in the presence of sexual stimulation. The agency's detailed clinical review of the studies on the product, approval letter, professional labeling, and information for consumers may be found on the Internet at http://www.fda.gov/cder/consumerinfo/viagra/viagra.htm.
Nightingale SL. Viagra Approval Information on the Internet. JAMA. 1998;279(21):1684. doi:10.1001/jama.279.21.1684