RESUMEN
Introduction: Self-medication is a prevalent behavior with significant health implications. Understanding its psychosocial determinants can inform preventative strategies and interventions. Methods: We evaluated the psychometric properties of the Self-Medication Behavior Inventory (SMBI-9) in a binational study with 779 Colombian and Mexican participants. Concurrent validity was assessed through correlations with related inventories, and confirmatory factor analysis tested the proposed four-factor model. Results: The SMBI-9 demonstrated high model fit (CFI = 0.995, TLI = 0.991) and invariance across countries. The factors-Social Influence, Attitude toward Medicine, Avoidance, and Prevention-varied significantly with knowledge of medicine, schooling, health insurance status and gender, underscoring the role of social and personal beliefs in self-medication practices. Discussion: SMBI-9 emerged as a reliable tool for capturing the multifaceted nature of self-medication behaviors. Findings highlight the influence of social norms and personal attitudes, suggesting targeted approaches for behavioral interventions.