Depression and antecedent medication adherence in a cohort of new metformin users.

AIMS: The association between depression and poor medication adherence is based on cross-sectional studies and cohort studies that measure adherence rates after depression status is determined. However, depressive symptoms occur well before diagnosis. This study examined adherence patterns in the year before a depressive episode. METHODS: This retrospective cohort study followed new metformin users identified in Alberta Health's administrative data between 2008 and 2018. Depressive episodes starting ≥1 year after metformin initiation were identified using a validated case definition. Controls were randomly assigned a pseudo depression date. Adherence to oral antihyperglycemic medications was estimated using proportion of days covered (PDC) and group-based trajectory models to explore the association between depression and poor adherence (PDC<0.8). RESULTS: A depressive episode occurred in 17,418 (10.6%) of 165,056 new metformin users. Individuals with depression were more likely to have poor adherence compared to controls (adjusted odds ratio 1.21; 95% CI 1.17, 1.26). Five trajectories were identified: nearly perfect adherence (PDC >0.95 [34.8% of cohort]), discontinued (PDC=0 [18.3% of cohort], poor initial adherence (PDC 0.75) that declined either rapidly (9.2% of cohort) or gradually (30.1% of cohort), and poor initial adherence (PDC 0.26) that increased gradually (7.6% of cohort). Individuals with depression were more likely to be in one of the four trajectories of poor adherence compared to controls (adjusted odds ratio 1.24; 95% CI 1.19-1.29). CONCLUSIONS: Poor medication adherence occurs in the year before a depressive episode; therefore, poor medication use patterns could be used as an early warning sign for depression.

Association Between Antidepressant Use and Adherence to Anti-hyperglycemic Medications in Adults With Type 2 Diabetes and Depression: A Retrospective Cohort Study.

OBJECTIVES: Depression is a known risk factor for poor medication adherence, but it is unclear whether depression treatment affects adherence rates. In this study, we examined the association between pharmacologic treatment of a new depressive episode and subsequent adherence to oral anti-hyperglycemic medications. METHODS: In this retrospective cohort study we used administrative health data to follow adult new metformin users in Alberta, Canada, between 2008 and 2018. Depressive episodes starting ≥1 year after metformin initiation were identified and individuals starting antidepressant treatment within the first 90 days were compared with those who did not. The proportion of days covered (PDC) with oral anti-hyperglycemic medications in the subsequent year (days 91 to 455) was used to estimate adherence. The association between antidepressant treatment and poor adherence (PDC<0.8) was examined using multivariate logistic regression models. RESULTS: A new depressive episode occurred in 6,201 people, with a mean age of 56.0 (standard deviation [SD], 15.4) years. Of this cohort, 3,303 (53.2%) were women. Mean PDC was 0.55 (SD, 0.41); 924 (57.0%) of 1,621 people who started antidepressant treatment and 2,709 (59.2%) of 4,580 controls had poor adherence (p=0.13). After adjusting for baseline comorbidities and other characteristics, antidepressant treatment was associated with a lower likelihood of poor adherence (adjusted odds ratio, 0.85; 95% confidence interval, 0.75 to 0.96; p=0.007). CONCLUSIONS: Although overall adherence to anti-hyperglycemic medications was low after onset of a depressive episode, antidepressant treatment was associated with a lower likelihood of poor adherence.