Background: Mental health (MH) polypharmacy, defined as prescribing multiple mental health medications for the same condition, presents significant challenges in clinical practice. With varying prevalence rates and an increasing trend, particularly in the UK, this deprescribing prospective quality improvement project aimed to address the complexities and risks associated with MH polypharmacy. Patients and Methods: A large primary care centre in London was selected for this project. Electronic records of 667 patients (non-coded in mental health lists) were analysed as a result of the absence of a Systematised Nomenclature of Medicine Clinical Terms (SNOMED CT) for mental health. Seventy-two non-coded patients exhibiting “same-class” as well as “adjunctive” and “augmentation” polypharmacy were identified. Their demographic and health data, including MH diagnoses, physical status, and lifestyle habits, were evaluated. This deprescribing prospective project included 68 patients and employed a model inspired by the Plan–Do–Study–Act (PDSA) cycle, focusing on reducing psychotropic, adjunctive, and augmentative medications while monitoring mental health control through face-to-face consultations using the Patient Health Questionnaire-9 (PHQ-9) and Generalised Anxiety Disorder Assessment-7 (GAD-7) scores, alongside physical health parameters. Results: The project revealed a significant decrease in the average number of psychotropic and adjunct medications from initial consultations to the end of the 18-month period. Additionally, a marked reduction in reported side effects and drug interactions was observed. Improvements in mental health control, as evidenced by PHQ-9 and GAD-7 scores, were noted. Physical health parameters, including BMI, blood pressure, heart rate, HbA1c, and cholesterol levels, also showed significant improvements. Educational initiatives for patients and clinicians were successfully implemented, contributing to these positive outcomes. Discussion: The project faced challenges like balancing medication reduction with mental health stability, patient apprehension, and the absence of standardised protocols. However, the successful reduction in medication numbers and the improvement in health outcomes highlight the effectiveness of the model. This project underscores the necessity of a tailored approach to MH polypharmacy, emphasising continuous education, clinical titration, and adherence to guidelines. Future research is needed to develop clear guidelines for medication combination in mental health care and to understand the long-term effects of polypharmacy in mental health populations. Conclusions: This project demonstrates the potential for significant improvements in the management of MH polypharmacy. By carefully managing medication reductions and employing a comprehensive care approach, including patient education and clinician training, the project achieved improvements in both mental and physical health outcomes. These findings suggest a promising direction for future practices in MH polypharmacy management.