The main objective of this study was to assess the effectiveness of a pharmacist-led medication therapy management through level of medication adherence and relapse rate among psychiatric patients in mental health facility setting in Davao City. There were fifteen psychiatric out-patients’ respondents with schizophrenia, bipolar disorder and major depressive disorder. This study utilized the pretest-posttest design with quantitative-qualitative explanatory mixed sequential method. The researcher used the mean and paired sample t-test as statistical tools. A modified research instrument was developed, validated and pilot tested. Findings revealed that the WHO medication adherence barriers namely, socio-economic, therapy, patient, condition and healthcare team or healthcare system related factors affects patient’s medication adherence that lead patients to relapse. Meanwhile, pre-intervention results depicted that psychiatric patients were slightly adherent to medication and experienced slight recurrence of symptoms or relapse. With this, to address the barriers of medication adherence causing relapse, the researcher conducted patient tailored interventions, medication therapy management and developed treatment plan to promote patients’ adherence to medication. Further, post-intervention result revealed psychiatric patients became highly adherent to medication and did not experience relapse symptoms.