Aims To investigate short‐ and long‐term effects of real‐time monitoring medication use combined with short message service (SMS) reminders for missed doses on refill adherence to oral anti‐diabetic medication. Methods A randomized controlled trial with two intervention groups and one control group involving 161 participants with Type 2 diabetes with suboptimal adherence. For 6 months, participants in the SMS group (n = 56) were monitored and received SMS reminders if they missed their medication. Participants in the non‐SMS group (n = 48) were only monitored. The control group (n = 57) was not exposed to any intervention. Primary outcome measure was refill adherence to oral anti‐diabetic medication. Multi‐level regression analyses were performed to examine intervention effects on adherence between and within groups after 1 and 2 years of follow‐up. Results At baseline, mean refill adherence was comparable between the groups. After 1 year, adherence in the SMS group was significantly higher than in the control group (79.5% vs. 64.5%; P < 0.001) and showed a significant improvement from baseline (+16.3%; P < 0.001). Mean adherence in the non‐SMS group reached 73.1% (+7.3%; P < 0.05), but did not differ from the control group (P = 0.06). After 2 years, the improved adherence in the SMS group persisted and remained significantly higher than in the control group (80.4% vs. 68.4%; P < .01), contrary to the non‐SMS group whose adherence approached baseline level again (65.5%). Conclusions This study shows the long‐term effectiveness of real‐time medication monitoring combined with SMS reminders in improving refill adherence. This new reminder system can strengthen the self‐management of people with diabetes. What's new? The innovative real‐time medication monitoring system evaluated in this study is the first to provide the opportunity to intervene only when patients forget to take their medication. This study showed that receiving short message service (SMS) reminders only when a dose is missed results in a higher refill adherence, and is the first to demonstrate long‐term effectiveness of electronic reminders on adherence. The real‐time medication monitoring reminder system can especially provide support for people who have problems taking their medication because of forgetfulness. This system can also strengthen a person's self‐management, as medication management is an important aspect of self‐management.