Longitudinal association between medication adherence and glycaemic control in Type 2 diabetes

AIM: Despite the widespread assumption that adherence drives glycaemic control, there is little published support for this in Type 2 diabetes. The study objective was to determine whether self-reported medication adherence predicts future glycaemic control in Type 2 diabetes, after accounting for baseline control. METHODS: Medication adherence (4-item Morisky scale), glycaemic control (HbA(1c)%), and other variables were assessed in 287 adult primary care patients prescribed oral medication (40% also on insulin) for Type 2 diabetes. Glycaemic control was reassessed 6 months later. Regression analyses examined concurrent and future glycaemic control as a function of baseline medication adherence after adjustment for baseline glycaemia and other potential confounders. RESULTS: Only half of patients reported high adherence. Cross-sectional adjusted analysis replicated prior reports of an adherence-HbA(1c) association (P = 0.011). Even after adjusting for baseline HbA(1c), each one-point increase in baseline Morisky total score was associated with a 1.8 mmol/mol (or 0.16%) increase in HbA(1c) measured 6 months later. Additionally, baseline endorsement of forgetting to take medication was associated with a 4.7 mmol/mol (or 0.43%) increase in 6-month HbA(1c) (P = 0.005). This effect persisted after adjusting for psychological distress and did not vary by key demographic and medical features. CONCLUSIONS: Even after stringent adjustment for baseline glycaemic control, self-reported adherence to diabetes medication predicts long-term glycaemic control. The Morisky scale is an easy-to-use clinical tool to identify patients whose glycaemic control will subsequently worsen, regardless of age, gender and psychological distress.