Adherence patterns to cardiovascular medications in people with type 2 diabetes mellitus: a retrospective cohort study using group-based trajectory analysis in primary care

To assess adherence to glucose-, lipid-, and blood pressure-lowering medications in people with T2DM and identify predictors of non-persistent adherence behaviours. We conducted a retrospective cohort study using primary care data from 2013 to 2023 for people diagnosed with T2DM. Medication adherence was assessed over 60 months, defined as receiving at least one prescription every six months. Group-Based Trajectory Analysis (GBTA) identified adherence patterns. Multinomial logistic regression explored predictors of trajectory membership. Three consistent adherence trajectories were observed across all medication classes: persistent adherence (40.6 %-44.3 %), gradual decline (32.7 %-36.6 %), and early discontinuation (21.0 %-26.7 %). Persistent adherers maintained high adherence (0.70-0.76) at 60 months. Gradual decliners exhibited a steady decrease in adherence from approximately 0.84 at 12 months to below 0.20 at 60 months. Early discontinuers ceased therapy almost entirely by 24 months. Key risk factors for early discontinuation included female sex (glucose-lowering: RRR 0.72; 95 % CI: 0.57-0.92 for males vs females), metropolitan residence (RRR 1.38; 95 % CI: 1.07-1.78), and having an elevated LDL cholesterol in the lipid-lowering cohort (RRR 1.75; 95 % CI: 1.36-2.26). This study highlights distinct long-term adherence patterns among individuals with T2DM, with over half showing non-persistent use over a five-year period, falling into either early discontinuation or gradual decline groups. These trajectories, while both clinically significant, likely reflect different underlying factors and underscore the need for tailored intervention strategies to support sustained treatment adherence.