In the U.S., Medicare Part D coverage gap poses concern for antidepressant adherence, but wide availability of generic antidepressants may mitigate the effect.

To assess the effects of coverage gap and generic prescribing on antidepressant adherence among a cohort of Medicare patients experiencing a new episode of depression.

We used 2007 Medicare Part D drug event file to examine antidepressant use over the 6 months following antidepressant initiation. We estimated Cox proportional hazard models to assess the effects of the two factors on the risk of antidepressant treatment disruption. We estimated mixed-effects linear models to assess the effects on monthly days of antidepressant possession. All analyses were stratified by Part D low-income subsidy (LIS) status and Medicare entitlement (aged vs. disabled).

Receiving a generic (vs. brand) antidepressant on the first script was associated with a significantly reduced risk of treatment disruption across all four populations: hazard ratios ranged from 0.66 (p = 0.006) among disabled patients not receiving LIS to 0.88 (p = 0.020) among aged patients receiving LIS. For patients not receiving LIS, experience of coverage gap was associated with increased risk of disruption only among the disabled (hazard ratio = 2.15, p = 0.006). Analysis of monthly antidepressant possession produced consistent results and indicated that the beneficial effect of generic first script was comparable with or outweighed the detrimental effect of coverage gap.

Part D coverage gap adversely affected antidepressant adherence by disabled patients not receiving LIS. Increased generic prescribing may help improve adherence among all patients.