Reduced Out-of-Pocket Costs and Medication Adherence - A Population-Based Study

Background: In 2007, a drug benefit plan for Seniors (SDP) was launched in Saskatchewan, Canada. SDP capped out-of-pocket costs at $15 per prescription for individuals aged 65 and older. Objectives: To quantify the impact of the SDP on chronic medication adherence.  Methods: A retrospective cohort study was conducted for participants aged 65 or older who were eligible to the SPD, controlled by a younger group aged 40 to 64 who were ineligible. Adherence was measured over 365 days using medication possession ratio (MPR). MPRs were compared between age groups, and between pre and post SDP-launch periods. The odds ratio of optimal adherence (i.e., MPR≥80%) was estimated using logistic regression models with generalized estimating equations (GEE). Results: Between 2005 and 2009, 353,568 adherence observations were observed from 188,109 unique patients. Comparing the post-SDP period vs before, the increase in the odds of optimal medication adherence was significant (OR=1.08, 95% CI: 1.04 to 1.11) and was stronger after excluding patients already receiving medication benefits from other government programs (OR= 1.21, 95% CI: 1.16 to 1.26). The SDP was associated with improved adherence among the subgroup of prevalent medication users (OR=1.08, 95% CI: 1.04 to 1.12), but not incident users (OR=1.05, 95% CI: 0.98 to 1.13). Conclusion: Reducing out-of-pocket medication costs for seniors was associated with small improvements in medication adherence across the population.