This randomized, rater-blind, multicenter clinical trial will evaluate whether a personalized pharmaco-lifestyle intervention improves mental functioning in adults with severe mental illness, including schizophrenia, bipolar disorder, or major depressive disorder. Participants will be randomized to either a modular individualized intervention program or a structured psychoeducation control condition. The individualized intervention may include physical exercise, an anti-inflammatory diet, sleep intervention, social prescribing, semaglutide for eligible participants with overweight or obesity, and optional closed-loop transcranial alternating current stimulation for participants with prominent depressive symptoms. The primary outcome is change in the SF-36 Mental Component Summary score from baseline to Month 3.