Introduction <p>Mental disorders are estimated to affect one in seven people globally and are often linked to premature mortality. Psychotropic medicines play an important role in the management of many mental health conditions particularly where symptoms are moderate to severe, persistent, or complex. Pharmacists are increasingly recognised as key members of multidisciplinary mental health teams, with their role focusing on safe and effective use of psychotropic medicines. Mental healthcare is increasingly delivered in outpatient settings, however, the impact of pharmacists on these services remains underexplored.</p> Aim <p>To systematically review and evaluate the impact of pharmacist-led or pharmacist-involved interventions specifically within outpatient mental health settings globally, across the full spectrum of mental disorders.</p> Method <p>A systematic search of five electronic databases (MEDLINE, Embase, CINAHL, CENTRAL, and PsycINFO) was conducted from inception to October 2025. Grey literature sources including ClinicalTrials.gov and Google Scholar were also searched. Inclusion criteria were: (i) evaluation of a pharmacist-led or pharmacist-involved intervention with a measurable outcome; (ii) conducted in an outpatient mental health setting involving adults with a diagnosed mental disorder classified according to ICD (up to and including ICD-11) or DSM criteria (up to and including DSM-5), excluding dementia; and (iii) inclusion of a comparator or control group. Study screening, data extraction, and quality appraisal, were performed independently by two reviewers. Due to heterogeneity in study design and outcomes, a narrative synthesis was conducted.</p> Results <p>Twenty-three studies met the inclusion criteria: 11 randomised controlled trials and 12 non-randomised studies. Pharmacist interventions varied, but most commonly included medication reviews, psychoeducation, adherence support and monitoring for side effects or drug interactions. Outcomes were grouped into seven domains: patient-reported, symptom-related, treatment-related, medication adherence, cost, monitoring and hospitalisations. Pharmacist impact was associated with improvements across multiple domains, particularly in medication adherence, treatment-related and symptom-related outcomes. While outcome measures varied between studies, a majority (82.6%) reported positive trends in at least one domain, favouring pharmacist-led or pharmacist-involved care over usual care.</p> Conclusion <p>Pharmacist-led interventions in outpatient mental health settings are associated with positive clinical and healthcare-related outcomes across a range of mental disorders globally. These findings support the integration of pharmacists into multidisciplinary outpatient mental health teams and highlight the need for more high-quality, standardised research to inform service development and policy.</p>