Aims: Suboptimal adherence to antipsychotics leads to poorer outcomes and relapse. Several factors, including the formulation and number of antipsychotics, may influence medication adherence. This study aimed to identify longitudinal adherence patterns to oral and long-acting injectable (LAI) antipsychotics in monotherapy/polypharmacy through group-based trajectory modelling (GBTM).
Methods: This was a retrospective cohort study that linked prescription and dispensing data of adult patients with a new antipsychotic prescribed between 2015 and 2019 in Catalonia (Spain). GBTM was used to classify patients following a similar longitudinal pattern of adherence. The response variable was adherence, estimated through the continuous medication availability measure (CMA), in each 30-day period during 12 months of follow-up. Baseline and treatment characteristics were used to characterize the trajectories identified.
Results: Among the 7730 patients included in the study, we identified seven clinically distinct trajectory groups of adherence to antipsychotics: non-initiation (19%), low implementation (9%), immediate discontinuation (6%), mid-discontinuation (5%), late-discontinuation (5%), high implementation (21%), and full implementation (35%). Trajectories with better adherence were more likely to receive the prescription from a psychiatrist, receive LAIs and have previous exposure to other antipsychotics. Intermittent medication use and high levels of polypharmacy were characteristics of the "low" and "high implementation" groups.
Conclusions: Targeting newly prescribed patients by improving the clinician-patient relationship could be particularly valuable, as they seem more likely to not initiate or discontinue treatment immediately compared to patients in other groups. Patients on polypharmacy should have more regular adherence monitoring and LAIs should be considered, as they appear to be associated with better adherence.
Keywords: antipsychotic medication; group‐based trajectory modelling; medication adherence; mental health; real‐world data.
© 2025 British Pharmacological Society.