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Table 1.  Effect of Plans’ Narrow Network Implementation on Patients’ MPR
Effect of Plans’ Narrow Network Implementation on Patients’ MPR
Table 2.  Comparison of Narrow Network Implementation’s Effect on MPR by Plans’ Use of 90-Day Supply Programs
Comparison of Narrow Network Implementation’s Effect on MPR by Plans’ Use of 90-Day Supply Programs
Research Letter
November 2015

Association Between Narrow Pharmacy Networks and Medication Adherence

Author Affiliations
  • 1Policy Research Group, Enterprise Analytics, CVS Health, Cumberland, Rhode Island
JAMA Intern Med. 2015;175(11):1850-1853. doi:10.1001/jamainternmed.2015.4582

In narrow or preferred pharmacy networks, in-network pharmacies negotiate reduced prescription prices with insurance plans. Plans then offer their members reduced cost sharing to incentivize in-network pharmacy use, thereby increasing the network’s prescription volume. In 2014, 75% of Medicare Part D and 70% of exchange plan enrollees were in a narrow or preferred network drug plan. Narrow networks are common in commercial plans as well.1 Concerns have been raised that these networks adversely affect medication adherence owing to reduced geographic access.2,3 Others argue that networks encourage members to establish a pharmacy home where pharmacists can better support adherence and coordinated care.4 We assessed the effect of narrow network implementation on members’ medication adherence. We also examined whether pre-post adherence changes between plans that implemented narrow networks and those that did not were different in the following 2 subgroups: plans with and plans without 90-day prescription programs, which are known to boost adherence. Combined with narrow network implementation, these programs may be associated with synergistic improvements in medication adherence.


Eligible members were enrolled for all 12 months of 2012 and/or 2013 (January 1 through December 31, 2012, and/or January 1 through December 31, 2013) in commercial drug plans that implemented narrow networks in 2013 or 2014. Data analysis took place from January 1, 2012, through December 31, 2013. The network design provided minimal or no reimbursement for costs associated with prescriptions filled at out-of-network pharmacies. Members’ deidentified data were used as permitted by the Health Insurance Portability and Accountability Act. Institutional review board approval was not needed for this study. Plans that implemented narrow networks in 2013 were considered intervention plans; those that implemented them in 2014 were considered control plans. For all plans, CVS/caremark was the pharmacy benefits manager. Using difference-in-difference analyses, controlling for the clustering of members in plans, we assessed the differences in members’ medication-possession ratio (MPR) before (2012) and after (2013) network implementation separately for statins, antihypertensive medications, oral antidiabetic medications, and antidepressant medications. The MPR was defined as the days’ supply from the first through last times that the prescription was filled divided by the days between the first fill date and December 31 of that year. In an interaction analysis, we explored whether MPR differences before and after narrow network implementation between the intervention and control plans differed significantly between the following 2 subgroups: plans with 90-day prescription programs in place in both 2012 and 2013 and plans without these programs.


Two narrow network plans (67 906 members) and 3 nonnetwork plans (149 989 members) were analyzed. Although both network and nonnetwork plans’ MPRs improved between 2012 and 2013, individuals enrolled in narrow network plans had greater increases in MPR than individuals enrolled in nonnetwork plans (MPR for statins: 1.65% [95% CI, 1.35%-1.92%]; for antihypertensive medications: 1.34% [95% CI, 1.11%-1.56%]; for antidiabetic medications: 0.95% [95% CI, 0.43%-1.45%]; and for antidepressants, 1.00% [95% CI, 0.73%-1.31%]) (Table 1). The difference in MPR improvements before and after network implementation between network plans and nonnetwork plans was greater for plans that had 90-day programs already in place. Increases in MPR among patients who were taking statins were 0.63% (95% CI, 0.58%-0.68%) greater after narrow network implementation in plans with programs vs those without programs; among those taking antihypertensive medications, the MPR increase was 0.89% (95% CI, 0.72%-1.05%), the MPR increase among those taking antidiabetic medications was 1.72% (95% CI, 1.45%-1.99%), and the MPR increase among those taking antidepressant medications was 1.02% (95% CI, 1.01%-1.03%) (Table 2).


Among commercial health plan members, implementation of a narrow pharmacy benefit network was not associated with reduced adherence to 4 medication types; in fact, we observed slight but consistent adherence improvements. We did not assess the clinical differences associated with these adherence changes. Control plans had higher MPRs than intervention plans, reducing their ability to improve adherence. CVS/caremark administers adherence programs for all its plans, so any bias introduced by such programs would be nondifferential between the intervention and control plans. Although our results may not generalize to prescription drug plans that are managed by other pharmaceutical benefit managers or other narrow network designs, our study suggests that incorporating a narrow network feature into a plan’s benefit design slightly improves and does not adversely affect medication adherence. The narrow network approach, when permitted, merits consideration by plans and payers who seek to optimize their members’ drug adherence while reducing overall health care costs.

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Article Information

Corresponding Author: Jennifer M. Polinski, ScD, MPH, CVS Health, 100 Scenic View Dr, Office No. 121130, Cumberland, RI 02864.

Author Contributions: Dr Polinski had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Polinski, Matlin, Gagnon, Brennan, Shrank.

Acquisition, analysis, or interpretation data: Polinski, Matlin, Sullivan, Gagnon, Shrank.

Drafting of the manuscript: Polinski.

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

Statistical analysis: Polinski, Sullivan, Gagnon.

Administrative, technical, or material support: Polinski, Matlin, Gagnon, Brennan, Shrank.

Study supervision: Polinski, Matlin, Shrank.

Published Online: September 8, 2015. doi:10.1001/jamainternmed.2015.4582.

Conflict of Interest Disclosures: All the authors report being employees of and holding stock in CVS Health.

Funding/Support: This study was supported by CVS Health.

Role of the Funder/Sponsor: CVS Health was involved in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, and approval of the manuscript; and the decision to submit the manuscript for publication.

Gebhart  F.  Pharmacy benefits move to narrower networks. Drug Topics website. Published March 10, 2014. Accessed February 4, 2015.
Consumers Union; HealthHIV; Medicare Rights Center; National Grange National Rural Health Association; National Senior Citizens Law Center.  Re: The Ensuring Seniors Access to Local Pharmacies Act (HR 4577) [letter]. Accessed February 4, 2015.
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