Purpose <p>This study aimed to investigate the effect of using a reminder-based mobile application on medication adherence in patients who underwent total thyroidectomy.</p> Materials and methods <p>This randomized controlled trial followed CONSORT guidelines and included 63 patients who underwent total thyroidectomy at a university and a state hospital. The intervention group (<i>n</i> = 31) used a reminder mobile application for 8 weeks, while the control group (<i>n</i> = 32) received standard care. Data were collected at weeks 1, 4, and 8 using a personal information form, follow-up form, and Morisky eight-item medication adherence scale. Statistical analyses included chi-square, <i>t</i>-test, ANOVA, Mann–Whitney <i>U</i>, and Friedman tests.</p> Results <p>At week 4, the intervention group demonstrated significantly higher mean MMAS-8 scores compared to the control group (6.58 vs. 5.71, <i>p</i> = 0.016). Furthermore, at week 8, a statistically significant difference was observed between groups in terms of medication adherence levels based on MMAS-8 cutoff categories (<i>χ</i>² = 9.6, <i>p</i> = 0.008).</p> Discussion <p>This study showed that a reminder-based mobile application effectively improved medication adherence in patients after total thyroidectomy. Increased adherence was observed in the intervention group, while a decline occurred in the control group. These findings indicate that reminder-based mobile health interventions may support medication adherence during the early postoperative period.</p> Conclusion <p>Reminder mobile applications can positively impact medication adherence. Integrating such tools into routine postoperative follow-up may support treatment continuity in patients receiving levothyroxine after total thyroidectomy.</p> ClinicalTrials.gov identifier <p>NCT05503576, registration date 08 December 2022.</p>