The study aims to evaluate the impact of integrating a clinical pharmacist into Flexible Assertive Community (FACT) teams on health-related quality of life and pharmacotherapy for individuals with severe mental illness and substance use disorders. This is a pragmatic effectiveness study using a stepped wedge cluster randomized trial design. Four FACT teams from FACT Innlandet will serve as clusters, transitioning from standard care (control) to intervention in a randomized sequence. The intervention involves integrating a clinical pharmacist into the interdisciplinary FACT teams. Participants will be adults (over 18 years old), receiving treatment from participating FACT teams, diagnosed with severe mental illness or substance use disorder and prescribed at least one psychotropic medication. Exclusion criteria include inability to provide informed consent, planned discharge within the first three months of period 1, or inability to communicate in Norwegian or English. The control group receives standard care provided by FACT teams. The intervention group will have a clinical pharmacist integrated into the FACT team performing medication reconciliation, comprehensive medication reviews, patient counselling, and interdisciplinary discussions to resolve medication-related problems. A sample size of 160 patients is estimated based on an effect size of 0.25, 80% power and alpha=0.05. The primary endpoint is change in patient-reported health related quality of life, measured using the EuroQoL-5 dimensions-5 levels (EQ-5D-5L) and Visual Analog Scale, EQ-VAS scores from baseline to the end of the intervention.