Background: Many managed care organizations use feedback based on electronically maintained claims data to alert physicians to potential treatment problems, including patient medication nonadherence. However, the efficacy of such interventions for improving adherence among patients treated for depression is unknown. Methods: We examined an antidepressant compliance program consisting of faxed alerts to physicians beginning May 2003 using interrupted time series analysis to evaluate its impact on rates of antidepressant adherence between May 2002 and May 2004 among members of the managed care plan of Harvard Pilgrim Health Care, which is a health plan operating in 3 states in New England, with corporate headquarters in Wellesley, Mass. The program alerted prescribing physicians to patients with gaps of more than 10 days in refilling antidepressant prescriptions during the first 180 days of treatment. Our outcome measures were rates of nonadherence among patients with refill gaps of more than 10 days (“delayed refill”) and proportion of days without treatment within the first 180 days of treatment. Results: A total of 13 128 patients ( >= 18 years of age) who were starting treatment with antidepressants met the study criteria. Rates of nonadherence among patients with delayed refills remained constant (P=. 22) over the 2-year study period, averaging 75% (95% confidence interval, 72.7%-77.3%). Rates of antidepressant nonadherence significantly increased over time ( P=. 04), with an average of 40% ( 95% confidence interval, 38.4%-41.6%) of days without dispensed antidepressants available during treatment episodes. Conclusions: Using real-time pharmacy information to alert physicians regarding patient adherence was not successful in increasing antidepressant adherence rates among members of the managed care plan. Effectiveness of electronically triggered, patient-specific, faxed feedback should be carefully evaluated before widespread implementation, because faxes are insufficient as a stand-alone policy tool.