In recent years, the U.S. government has designated funding of several large-scale initiatives for comparative effectiveness research (CER) in health care. The American Recovery and Reinvestment Act (ARRA) of 2009 apportioned more than $1 billion to support CER programs administered by the Department of Health and Human Services (DHHS), the National Institutes of Health (NIH), and the Agency for Healthcare Research and Quality (AHRQ). CER is generally defined as the undertaking of original research or systematic reviews of published literature in order to compare the benefits and risks of different approaches to preventing, diagnosing, or treating diseases. These approaches may include diagnostic tests, medications, medical devices, and surgeries. The overall goals of CER are to support informed health care decisions by patients, clinicians, payers, and policy makers and to apply its evidence to ultimately improve the quality, effectiveness, and efficiency of health care. To (a) provide managed care professionals with general definitions of CER, specifically as it is administered by AHRQ; (b) discuss the importance of CER to clinical and managed care pharmacists; and (c) summarize key methods and findings from AHRQ's 2007 comparative effectiveness review on therapies for rheumatoid arthritis (RA). As supported by AHRQ, CER is conducted in order to synthesize comprehensive evidence on the comparative benefits and harms of treatment interventions. The findings from comparative effectiveness reviews can thus contribute to informing therapeutic strategies and treatment decisions. In 2007, a multitude of RA treatment options and studies motivated AHRQ to commission a systematic comparative effectiveness review. Conducted by investigators at the RTI-University of North Carolina Evidence-Based Practice Center, the review included comparisons of synthetic disease-modifying antirheumatic drugs (DMARDs), biologic agents, synthetic DMARDs versus biologic agents, and various combination therapies. Head-to-head comparisons of synthetic DMARDs generally revealed no significant differences in long-term clinical and radiographic outcomes, or in functional capacity or health-related quality of life. Two nonrandomized prospective cohort studies and 1 open-label effectiveness trial reported no differences in ACR20 and ACR50 response rates in patients treated with the tissue necrosis factor (TNF)-alpha inhibitors etanercept and infliximab. Comparisons of TNF-alpha inhibitors generally indicated no significant differences in rates of adverse events, including serious infections, and no increases in rates over time. In comparisons of a biologic agent combined with methotrexate versus a biologic agent alone, combination therapies were generally associated with better clinical response rates and better outcomes of functional capacity and quality of life. The most common adverse events observed in studies on biologic agents were diarrhea, headache, nausea, rhinitis, injection site reactions, and upper respiratory tract infections.