Background: Non-adherence to antidepressant treatment is not routinely measured in practical clinical trials. It has not been related to outcomes in a large sample of adults with chronic and/or recurrent major depressive disorder (MDD) or any sample treated with antidepressant combinations.
Methods: Adult outpatients with chronic and/or recurrent MDD were randomized to 12 weeks of treatment with bupropion-SR plus escitalopram, venlafaxine-XR plus mirtazapine, or escitalopram plus placebo. We compared non-adherence (the frequency with which daily medications were not taken) and specifically the frequency of temporarily stopping and/or skipping medication, or reducing or increasing the dose across treatments in 567 participants using a self-report questionnaire collected at each visit. We tested the association between non-adherence, and both treatment type and outcomes.
Results: A non-adherence rate under 10% was reported by 77.9%, 70.9%, and 71.6% of participants during weeks 1-4, 5-12, and 1-12, respectively. Antidepressant combinations were associated with a higher non-adherence rate than monotherapy during weeks 1-4 and 1-12. During weeks 1-4, 24.1% stopped/skipped doses and 6.1% reduced the dose. During weeks 5-12, 34.7% stopped/skipped doses and 9.4% reduced the dose. Across 12 weeks, 43.2% stopped/skipped doses, and 12.9% reduced the dose. Stopping/skipping doses during all time frames and dose decreases during weeks 1-12 occurred most frequently with combination treatments. Non-adherence was unrelated to symptom remission, response, or symptom change.
Conclusions: With closely monitored treatment, non-adherence is low and unrelated to depressive symptom outcome. Nonadherence is highest with antidepressant combinations. Specific non-adherent events are most often sporadic.
Trial registration: ClinicalTrials.gov NCT00590863.