Intentional and unintentional non-adherence in hypertension: psychometric validation, adherence-complexity...

Non-adherence to antihypertensive therapy remains a major barrier to blood pressure (BP) control globally. The behavioural distinction between intentional (INA) and unintentional non-adherence (UNA) is underexplored in low- and middle-income countries. We aimed to validate the Spanish MMAS-8, identify adherence-complexity phenotypes, and assess the mediating role of adherence between regimen complexity and BP control. In this multicenter, cross-sectional study (2022-2024), 1144 hypertensive patients from Argentina were evaluated. Adherence was assessed using the Spanish MMAS-8. Psychometric validation included Cronbach's alpha and principal component analysis. INA and UNA were classified by domain-based response patterns. K-means clustering was applied to MMAS-8 items and regimen complexity (number of drugs, daily doses). Mediation analysis tested the indirect effect of adherence. The MMAS-8 showed acceptable reliability (α = 0.78) and a unidimensional structure. Full adherence was observed in 41.1%. Among non-adherent patients, 38.5% were INA, 33.6% UNA, and 27.9% mixed. Four phenotypes were identified: (1) high adherence/low complexity; (2) very low adherence/simple regimens; (3) moderate adherence/intermediate complexity; (4) low adherence/high complexity. Adherence significantly mediated the effect of complexity on BP control (β = 0.004; p < 0.001), while the direct effect was non-significant. Compared with phenotype 1, phenotype 2 showed 58% lower odds of control (OR 0.42; 95% CI 0.29-0.61) and phenotype 4 showed 32% lower odds (OR 0.68; 95% CI 0.49-0.94). The Spanish MMAS-8 is valid for this population. Adherence-complexity phenotypes reflect structural and behavioural barriers. Tailored interventions should address INA and UNA using adherence profiling, fixed-dose combinations, and social support.