Longitudinal association between medication adherence and glycaemic control in Type2 diabetes

Aim Despite the widespread assumption that adherence drives glycaemic control, there is little published support for this in Type2 diabetes. The study objective was to determine whether self-reported medication adherence predicts future glycaemic control in Type2 diabetes, after accounting for baseline control. Methods Medication adherence (4-item Morisky scale), glycaemic control (HbA1c%), and other variables were assessed in 287 adult primary care patients prescribed oral medication (40% also on insulin) for Type2 diabetes. Glycaemic control was reassessed 6months 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-HbA1c association (P=0.011). Even after adjusting for baseline HbA1c, each one-point increase in baseline Morisky total score was associated with a 1.8mmol/mol (or 0.16%) increase in HbA1c measured 6months later. Additionally, baseline endorsement of forgetting to take medication was associated with a 4.7mmol/mol (or 0.43%) increase in 6-month HbA1c (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.