BackgroundPharmacist’s involvement in optimizing medication adherence among diabetic patients has been implemented for over a decade. Diabetes Medication Therapy Adherence Clinic (DMTAC) was set up to educate diabetic patients, monitor treatment outcomes, and manage drug-related problems. While evidence shows that pharmacist-led DMTAC was effective in reducing HbA1c, there was limited data regarding the impact of different intervention types and default to follow-up on glycemic control.AimTo assess the impact DMTAC on glycemic control and the difference in glycemic control between hospital and health clinic settings as well as defaulter and non-defaulter. In addition, the impact of pharmacist’s interventions, DMTAC follow-up frequencies, and duration of diabetes on glycemic control were also determined.MethodsA retrospective study was conducted among diabetes patients under DMTAC care between January 2019 and June 2020 in five hospitals and 23 primary health clinics. Patients’ demographics data, treatment regimens, frequencies of DMTAC visits, defaulter (absent from DMTAC visits) and types of pharmacists’ intervention were retrieved from patients’ medical records and electronic database. HbA1c was collected at baseline, 4–6 months (post-1), and 8–12 months (post-2).ResultsWe included 956 patients, of which 60% were females with a median age of 58.0 (IQR: 5.0) years. Overall, the HbA1c reduced significantly from baseline (median: 10.2, IQR: 3.0) to post-1 (median: 8.8, IQR: 2.7) and post-2 (median: 8.3, IQR: 2.6%) (p< 0.001). There were 4317 pharmacists’ interventions performed, with the majority being dosage adjustment (n= 2407, 55.8%), followed by lab investigations (849, 19.7%), drugs addition (653, 15.1%), drugs discontinuation (408, 9.5%). Patients treated in hospitals received significantly more interventions than those treated in primary health clinics (p< 0.001). We observed significantly less reduction in HbA1c in DMTAC follow-up defaulters than non-defaulters after 1 year (− 1.02% vs. − 2.14%,p= 0.001). Frequencies of DMTAC visits (b: 0.19, CI: 0.079–0.302,p= 0.001), number of dosage adjustments (b: 0.83, CI: 0.015–0.151,p= 0.018) and number of additional drugs recommended (b: 0.37, CI: 0.049–0.691,p= 0.024) had positive impact on glycemic control whereas duration of diabetes (b: − 0.0302, CI: − 0.0507, − 0.007,p= 0.011) had negative impact.ConclusionGlycemic control improved significantly and sustained up to one year among patients in pharmacists-led DMTAC. However, DMTAC defaulters experienced poorer glycemic control. Considering more frequent visits and targeted interventions by pharmacists at DMTAC resulted in improved HbA1c control, these strategies should be taken into account for future program planning.