This systematic review aims to determine the effect of MTM carried out by pharmacists on achieving medication adherence and clinical outcomes in diabetes mellitus patients. The journal search method was taken from PUBMED, Scopus, and Google Scholar using the keywords "diabetes mellitus", "DM", "medication therapy management", "MTM", "clinical outcome", "clinical results", "adherence", and " treatment compliance”. The research identified came from Indonesia, the United States, Ethiopia, Brazil, New Zealand, Japan, Lebanon, and Malaysia. Out of the 169 studies identified, twenty-five met the inclusion and exclusion criteria, consisting of 5 RCTs, seven cohorts, and 13 quasi-experiments. MTM improves compliance and clinical outcomes of DM patients. Compliance increased from 80.5% to 87.5% (p<0.05). The average HbA1c value decreased from 10.5 to 8.2 (p<0.05), the average systolic blood pressure (SBP) decreased from 142.7 mmHg to 135.6 mmHg (p<0.05), mean diastolic blood pressure (DBP) decreased from 89.9 mmHg to 83.6 mmHg (p<0.05), and mean fasting plasma glucose (FPG) decreased from 218.5 mg/dl to 142.4 mg/dl (p<0.05). Overall, this study shows that pharmacist-provided MTM services can improve clinical outcomes and medication adherence in patients with diabetes.