Abstract Background: A rise in the number of people with diabetes is possible if immediate action is not taken to reverse the trend. Diabetes mellitus is a chronic medical condition that has serious health consequences for people. The goal of this study was to investigate the relationships between medication adherence, health literacy, and demographic characteristics. Materials and Methods: This correlational study methodology was used at the University of Benin Teaching Hospital in Benin City in 2020. The study included 180 diabetes participants. The tools used included belief about medications questionnaires (BMQ), medication adherence rating scales (MARS), and the Short Functional Health Literacy in Adults Test (STOHFLA), and used linear regression, descriptive statistics, and Spearman’s rho correlation. Results: The researcher discovered that 66.7% of the people lacked adequate health literacy, and MARS analysis revealed that medication adherence was low. Age and income level both had relationships with medication adherence, but marital status, and education did not. The researcher also found a link between medication adherence, health literacy, and medication belief using P-values of 0.004 and 0.002. The regression model indicates that age, medication belief, health literacy, and economic and income level are predicting factors for medication adherence. Conclusion: Nurses and hospital administrators need to focus more on the health literacy, age, income level, and health beliefs of their patients because there is evidence that these aspects are statistically associated with medication adherence.