Medication Adherence in Adults with Type 2 Diabetes Mellitus Across Gulf Cooperation Council Countries: A Scoping Review of Determinants, Measurement Approaches, and Intervention Evidence

Background/Objectives: The prevalence of type 2 diabetes mellitus (T2DM) is a significant public health concern in the Gulf Cooperation Council (GCC) countries. Medication adherence is critical in achieving glycaemic control. This scoping review synthesizes recent evidence on medication adherence among patients with T2DM in GCC countries, focusing on determinants and strategies to enhance adherence. Methods: This registered scoping review was developed based on articles published between January 2020 and July 2026, retrieved through searches in PubMed, Scopus, Web of Science, and the Saudi Digital Library. Data were gathered on study design, setting, adherence measurement tools, reported adherence levels, determinants, and interventions. Results: Of 3457 records screened, 549 reports were assessed for eligibility, and 78 studies met the inclusion criteria. Individual studies reported variable and frequently suboptimal medication adherence among adults with T2DM in GCC countries. These study-specific estimates varied widely according to the clinical setting, population, measurement instrument and adherence threshold. Associated factors were patient-related (knowledge, beliefs, and health literacy), therapy-related (regimen complexity, polypharmacy, and side effects), healthcare system-related (continuity of care, patient–physician communication, and access to medicines), and sociocultural (family support, stigma, and religious practices, including Ramadan fasting). Digital health applications, SMS-based interventions, pharmacist-led interventions, and culturally oriented education programs may offer potential benefits for adherence. Nevertheless, their implementation and evaluation remain inconsistent. Conclusions: The available evidence was geographically and methodologically uneven, with considerable heterogeneity in adherence measurement. Standardized measurement approaches and adequately designed longitudinal and intervention studies are needed to strengthen medication-adherence research and practice across GCC countries.