Long-acting injectable antipsychotics in forensic psychiatric populations: a systematic review of adherence, relapse, violence, and reoffending outcomes

Long-acting injectable (LAI) antipsychotics are increasingly used in forensic psychiatric services to address treatment non-adherence. Their effectiveness within forensic psychiatric services has not previously been systematically evaluated. This systematic review was prospectively registered with PROSPERO (CRD420261283093) and conducted according to PRISMA guidelines. Embase, PsycINFO, MEDLINE, and PubMed were searched to identify studies evaluating LAI antipsychotics in adults with schizophrenia-spectrum disorders managed within forensic psychiatric services or closely related justice-involved pathways. Primary outcomes included treatment adherence, relapse, rehospitalisation, violence, offending or reoffending, and progression through forensic care pathways. Findings were synthesised narratively. Five studies involving 761 participants met the eligibility criteria, comprising one pragmatic randomised controlled trial in a justice-involved population (n = 444) and four observational studies in forensic services (n = 317). Evidence consistently supported improved treatment adherence or treatment continuation with LAI antipsychotics. Observational forensic studies reported favourable trends in adherence, relapse, hospitalisation, selected violence-related outcomes, and progression through secure care, but were limited by small sample sizes, methodological heterogeneity, and predominantly observational designs. Overall certainty of evidence was low for adherence and relapse outcomes and very low for violence and offending outcomes. Current evidence supports LAI antipsychotics as one component of comprehensive forensic psychiatric care, particularly for individuals with recurrent treatment non-adherence. While evidence supports improved treatment adherence, evidence for reductions in violence and offending remains limited.