Objective: To determine medication adherence and predictors of suboptimal adherence in a community cohort of patients with diabetes and to test the hypothesis that adherence decreases with increased number of medicines prescribed.

Research design and methods: A total of 128 randomly selected patients with type 2 diabetes from a single community health center responded to a pharmacist-administered questionnaire regarding medication use. Survey data were linked to clinical data available from the electronic medical record. We assessed self-reported adherence rates for each diabetes-related medicine, barriers and attitudes regarding medication use, and HbA(1c), total cholesterol, and blood pressure levels.

Results: Patients were taking a mean of 4.1 (+/-1.9) diabetes-related medicines. The average 7-day adherence was 6.7 +/- 1.1 days. Total number of medicines prescribed was not correlated with medication adherence. Adherence was significantly lower for medicines not felt to be improving current or future health (6.1 vs. 6.9 days out of 7, P < 0.001). Among patients on three or more medicines, 71% (15 of 21 patients) with suboptimal adherence were perfectly adherent with all but one medicine. Side effects were the most commonly reported problem with medication use. Of 29 medicines causing side effects that interfered with adherence, 24 (83%) did so for >1 month, and only 7 (24%) were reported to the patient's primary care physician.

Conclusions: In this sample, patients reported very high medication adherence rates regardless of number of medicines prescribed. Among patients on multiple medicines, most patients with suboptimal adherence were perfectly adherent to all but one medicine. Unreported side effects and a lack of confidence in immediate or future benefits were significant predictors of suboptimal adherence. Physicians should not feel deterred from prescribing multiple agents in order to achieve adequate control of hyperglycemia, hypertension, and hyperlipidemia.