Although evidence-based pharmacotherapies are a principal component of patient care, 30–50% of patients do not take their medications as prescribed. We conducted a randomized trial of two clinical decision support (CDS) interventions in 2219 patients: patient adherence reports to providers (n=744), patient adherence reports to providers + email notices to care managers (n=736), and controls (739). At 18-month follow-up, there were no treatment-related differences in patient medication adherence (overall, by medication class, and by medical condition). There also were no treatment-related differences in patient clinical and economic outcomes. Thus, while this study's CDS information interventions were successfully delivered to providers and care managers, and were effective in identifying medication adherence deficits and in increasing care manager responses to medication adherences issues, these interventions were not able to alter patient medication behavior.