Objective: To evaluate medication adherence, associated factors, and the role of pharmacists in adherence and outcome treatments in outpatients with diabetes at Hue University Hospital. Type 2 diabetes (T2DM) is a chronic illness that requires daily treatment. Poor adherence to antidiabetic medication can have negative consequences for patients. Data on medication adherence and programs to improve adherence for patients with diabetes in Vietnam are lacking. Methods: A pre-post study was conducted on 354 outpatients diagnosed with T2DM at Hue University Hospital. Participants were interviewed, counseled, and educated by a pharmacist once. The researchers assessed medication adherence levels and glycemic outcomes before and around three months after the intervention. Results: The prevalence of achieving adherence before the intervention was 65.0%. Factors associated with achieving medication adherence were medication regimen (P = 0.001) and controlled glycemic target (P < 0.001). The most common nonadherence behavior was forgetting to take antidiabetic medication. After the intervention, the prevalence of achieving adherence rose to 74.6%, and patients reported that they were more likely to remember to take antidiabetic medications (with statistical significance). The prevalence of achieving the glycemic target (both glycated hemoglobin and fasting plasma glucose) rose from 21.8% (before the intervention) to 31.1% (after the intervention). Conclusions: A significant proportion of patients did not achieve medication adherence. Medication adherence is associated with better glycemic outcomes. The role of pharmacists in patient education, medication counseling, and reminding is beneficial in terms of improving adherence levels and glycemic outcomes.