Background <p>Low adherence to lipid-lowering therapy (LLT) after myocardial infarction (MI) is associated with increased risk of recurrent cardiovascular events and death. However, little is known about long-term adherence patterns following treatment interruptions. The aim of this study was to describe adherence trajectories in MI patients following a LLT treatment gap, and model the impact of different adherence trajectories on estimated low-density lipoprotein cholesterol (LDL-C) levels.</p> Methods <p>We conducted a retrospective cohort study of 22,124 first-time MI patients in Sweden who dispensed statins and/or ezetimibe within 90&#xa0;days of their MI. Patients with a treatment gap &gt; 90&#xa0;days within three years post-MI were identified, and adherence trajectories were evaluated over a five-year period following the treatment gap using group-based trajectory modelling. Associations between adherence trajectories and patient characteristics were analyzed, and the impact on estimated LDL-C levels was simulated based on trajectory-specific adherence.</p> Results <p>Patients were categorized in six different adherence trajectories — constant adherent (34%), constant non-adherent (26%), rapidly (7%) and slowly (6%) increasing and rapidly (9%) and slowly (19%) decreasing adherence. Patients with a constant adherent trajectory were more often managed in primary care (compared to hospital care). Lower age and male sex were also associated with a constant adherent trajectory. The average LDL-C level in patients with a constant adherence trajectory was estimated to be 1.0&#xa0;mmol/L lower compared to patients with a constant non-adherence trajectory.</p> Conclusions <p>Suboptimal adherence following a treatment gap is common and has a clinically significant impact on the degree of LDL-C lowering.</p> Graphical abstract <p></p>