Depression in Patients with Type 2 Diabetes: Impact on Adherence to Oral Hypoglycemic Agents

Background: Adherence to oral hypoglycemic agents (OHAs) is important for adequate glycemic control and prevention of future complications in patients with type 2 diabetes. Objective: To examine the impact of depression on adherence to OHAs in patients newly diagnosed with type 2 diabetes. Methods: Patients newly diagnosed with type 2 diabetes during a 4 year period were identified from a Medicaid claims database. Presence of preexisting depression was determined on the basis of ICD-9-CM codes. Adherence to OHAs was computed using prescription refill data for a 12 month follow-up period from the date of the index OHA prescription. Two separate adherence indices (Medication Possession Ratio-1 [MPR-1], Medication Possession Ratio-2 [MPR-2]) were computed. The impact of depression on adherence was assessed after controlling for confounders such as demographics, comorbidity, provider interaction, complexity of regimen, and diabetes severity. Results: A total of 1326 newly diagnosed patients with type 2 diabetes were identified (depressed = 471; nondepressed = 855). Results of the study indicated that patients with depression had significantly lower adherence (MPR-1 86%; MPR-2 66%) to OHAs compared with patients without depression (MPR-1 89%; MPR-2 73%). Multivariate results indicated that depression was a significant predictor of adherence, with depressed patients being 3–6% less adherent to OHAs than nondepressed patients, after controlling for confounding factors. Conclusions: Depression significantly impacts adherence to OHAs in patients with type 2 diabetes. The study results imply that depression screening and treatment need to be included in the protocol for management of patients with type 2 diabetes.