Background: Approximately 20% to 50% of patients are not adherent to medical therapy. This review was performed to summarize, categorize, and estimate the effect size (ES) of interventions to improve medication adherence in chronic medical conditions.Methods: Randomized controlled trials published from January 1967 to September 2004 were eligible if they described 1 or more unconfounded interventions intended to enhance adherence with self-administered medications in the treatment of chronic medical conditions. Trials that reported at least 1 measure of medication adherence and 1 clinical outcome, with at least 80% follow-up during 6 months, were included. Study characteristics and results for adherence and clinical outcomes were extracted. In addition, ES was calculated for each outcome.Results: Among 37 eligible trials (including 12 informational, 10 behavioral, and 15 combined informational, be-havioral, and/or social investigations), 20 studies reported a significant improvement in at least 1 adherence measure. Adherence increased most consistently with behavioral interventionsthatreduceddosingdemands(3of3studies,large ES [0.89-1.20]) and those involving monitoring and feedback (3 of 4 studies, small to large ES [0.27-0.81]). Adherence also improved in 6 multisession informational trials (small to large ES [0.35-1.13]) and 8 combined interventions (small to large ES [absolute value, 0.43-1.20]). Eleven studies(4informational,3behavioral,and4combined)demonstrated improvement in at least 1 clinical outcome, but effects were variable (very small to large ES [0.17-3.41]) and not consistently related to changes in adherence.
Conclusion:Several types of interventions are effective in improving medication adherence in chronic medical conditions, but few significantly affected clinical outcomes.