Importance: Medication therapy management (MTM) services (also called clinical pharmacy services) aim to reduce medication-related problems and their downstream outcomes. Objective: To assess the effect of MTM interventions among outpatients with chronic illnesses. Data Sources: MEDLINE, Cochrane Library, and International Pharmaceutical Abstracts through January 9, 2014. Study Selection: Two reviewers selected studies with comparators and eligible outcomes of ambulatory adults. Data Extraction and Synthesis: Dual review of titles, abstracts, full-text, extractions, risk of bias, and strength of evidence grading. We conducted meta-analyses using random-effects models. Main Outcomes and Measures: Medication-related problems, morbidity, mortality, quality of life, health care use, costs, and harms. Results: Forty-four studies met the inclusion criteria. The evidence was insufficient to determine the effect of MTM interventions on most evaluated outcomes (eg, drug therapy problems, adverse drug events, disease-specific morbidity, disease-specific or all-cause mortality, and harms). The interventions improved a few measures of medication-related problems and health care use and costs (low strength of evidence) when compared with usual care. Specifically, MTM interventions improved medication appropriateness (4.9 vs 0.9 points on the medication appropriateness index, P < .001), adherence (approximately 4.6%), and percentage of patients achieving a threshold adherence level (odds ratios [ORs] ranged from 0.99 to 5.98) and reduced medication dosing (mean difference, -2.2 doses; 95% CI, -3.738 to -0.662). Medication therapy management interventions reduced health plan expenditures on medication costs, although the studies reported wide CIs. For patients with diabetes mellitus or heart failure, MTM interventions lowered the odds of hospitalization (diabetes: OR, 0.91 to 0.93 based on type of insurance; adjusted hazard rate for heart failure: 0.55; 95% CI, 0.39 to 0.77) and hospitalization costs (mean differences ranged from -$363.45 to -$398.98). The interventions conferred no benefit for patient satisfaction and most measures of health-related quality of life (low strength). Conclusions and Relevance: We graded the evidence as insufficient for most outcomes because of inconsistency and imprecision that stem in part from underlying heterogeneity in populations and interventions. Medication therapy management interventions may reduce the frequency of some medication-related problems, including nonadherence, and lower some health care use and costs, but the evidence is insufficient with respect to improvement in health outcomes
