<p>Risperidone in situ microparticles (risperidone ISM^®) is a novel long-acting prolonged-release formulation approved in the EU and USA for treating schizophrenia in adults. Once-monthly intramuscular injections of risperidone ISM^® provide immediate and sustained therapeutic levels of risperidone, eliminating the need for loading doses or oral supplementation. In the pivotal PRISMA-3 trial in patients with acute schizophrenia exacerbation, risperidone ISM^® significantly improved Positive and Negative Syndrome Scale (primary endpoint) and Clinical Global Impression-Severity of Illness (key secondary endpoint) total scores over the 12-week double-blind phase, with improvements observed as early as day 8. Continued treatment sustained efficacy over the 12-month open-label extension phase. Risperidone ISM^® also improved social functioning and had a positive impact on health-related quality of life. Patients stable on daily oral risperidone maintained their treatment benefits after switching to monthly risperidone ISM^®. Risperidone ISM^® was generally well tolerated in clinical trials, with a safety profile consistent with that of oral risperidone. Its fast onset of action, without the need for oral supplementation or loading doses, makes risperidone ISM^® a promising long-acting injectable that could enhance treatment adherence.</p>