Background: In older adults with multiple illnesses, medication regimens become increasingly demanding and can result in suboptimal adherence. We examine general social support, medication-specific social support and social conflict to identify possible mechanisms that operate in predicting adherence. Methods: Observational study with two measurement points, 6 months apart, with 309 multimorbid adults (ages 65þ). Adherence was regressed on general support, medication-specific support and social conflict while controlling for baseline adherence and covariates (sex, age, education, number of medicines, attitudes towards medicines and health status). Findings: Medication-specific support was the only, however negative predictor of adherence. Social conflict moderated this relation: Only in participants with high social conflict, medication-specific support was detrimental for adherence (OR¼0.42, p50.05). Discussion: These findings illustrate the need for a more refined analysis of various social factors that might enhance or compromise health behaviours in old age such as medication adherence.