Perceived Barriers as Key Behavioral Predictors of Medication Adherence in Older Adults with Diabetes in Northern Iran: Insights from the Health Action Process Approach

Background: Medication non-adherence remains a critical issue in older adults with type 2 diabetes. Understanding the behavioral determinants of adherence can help design more effective interventions. Purpose: This study aimed to identify behavioral predictors of medication adherence among community-dwelling older adults with type 2 diabetes in Iran using the full Health Action Process Approach (HAPA) model. Methods: In this cross-sectional study, 257 older adults were recruited from diabetes care centers in Gorgan, Golestan Province, Iran. Data were collected through structured interviews using a validated HAPA-based questionnaire and the 8-item Morisky Medication Adherence Scale (MMAS-8). Multiple linear and logistic regression models were used to evaluate associations between HAPA constructs and adherence. Results: Overall, 52% of participants were non-adherent. In univariate analyses, intention, coping self-efficacy, and action planning showed some association with adherence. In the adjusted model, only perceived barriers remained significant (B = 0.034, p = 0.001; OR = 1.035, 95% CI: 1.015– 1.055), with higher scores, indicating fewer perceived barriers, linked to increased odds of adherence. Conclusion: The findings highlight the dominant role of perceived barriers in shaping adherence behavior among older adults, overshadowing the effects of intention and planning. This suggests that interventions to improve adherence in this population should prioritize reducing contextual and psychological obstacles. Keywords: medication adherence, aged, diabetes mellitus, type 2, health behavior, health promotion