Development and Psychometric Validation of the ASMA Medication Adherence Questionnaire for Adults with Type 2 Diabetes in Saudi Arabia: A Cross-Sectional Study

Background and Purpose: Medication adherence remains a major challenge in the management of type 2 diabetes, contributing to poor glycaemic control, preventable complications, and increased healthcare burden despite advances in treatment. Existing adherence measures often quantify medication-taking behaviour but provide limited insight into the behavioural, psychological, and contextual determinants that influence long-term adherence. The aim of this study was to develop and psychometrically evaluate a theory-informed, patient-derived questionnaire (ASMA) to assess medication adherence and its behavioural determinants among adults with type 2 diabetes mellitus. Methods: His cross-sectional instrument development and validation study was conducted at a tertiary diabetes care centre in Riyadh, Saudi Arabia. Adults aged ≥ 18 years who had been receiving oral hypoglycaemic therapy for at least 12 months were recruited. Questionnaire items were derived from prior qualitative patient interviews and mapped to the Theoretical Domains Framework (TDF). Medication adherence outcomes were descriptively assessed using three self-reported items aligned with the ABC taxonomy of medication adherence, capturing initiation, implementation, and persistence of medication-taking behaviour. Results: A total of 145 participants were included (59.3% female), with a median diabetes duration of 10.5 years (IQR 6.0– 20.0). Most participants reported adherence across ABC phases: 91.8% reported always taking medication as prescribed (implementation), 97.9% reported initiation of therapy, and 84.2% reported persistent medication use. Sampling adequacy was acceptable (KMO=0.74), and Bartlett’s test was significant (χ 2 (325)=1214, p< 0.001). Exploratory factor analysis supported a four-factor structure after item refinement. The retained domains were: Psychological and Behavioral Regulation (9 items), Perceived Control and Treatment Facilitation (5 items), Knowledge and Informational Support (3 items), and Beliefs about Consequences (2 items). Factor loadings ranged from 0.69 to 0.82 within the unidimensional four-item domain. The four-factor solution demonstrated conceptual coherence and adequate variance explanation. Internal consistency was good for the Psychological and Behavioral Regulation domain (α=0.81; ω=0.83), while other domains showed moderate reliability, likely reflecting fewer items. Conclusion: The ASMA questionnaire demonstrates preliminary evidence of structural validity and reliability as a multidimensional, theory-informed instrument. It may support the identification of modifiable behavioural determinants of medication adherence and inform targeted, patient-centred interventions in adults with type 2 diabetes. Further confirmatory validation is warranted. Keywords: medication adherence, type 2 diabetes mellitus, questionnaire development, psychometrics, patient-reported outcomes