Use of antipsychotic medications, the top selling medication class in 2009 and a primary driver of recent growth in state Medicaid pharmacy expenditure, has changed dramatically in the past two decades since the introduction of several atypical antipsychotics. Recently, Food and Drug Administration (FDA) warnings and comparative effectiveness research have pointed to elevated risks associated with use of atypicals and have raised questions about their cost-effectiveness. Little is known about how psychiatrists adopt new medications, or whether and how they change their practice patterns when new evidence emerges on psychiatric drug efficacy and/or safety. Importantly, we know little about the provider-, organizational- and policy-level factors that promote or inhibit psychiatrists' response to new safety and efficacy information. Using unique physician-level data on antipsychotic prescribing for all psychiatrists who prescribe antipsychotic medications from IMS Health linked with physician characteristics from the AMA Masterfile, physician affiliations with health care organizations from the Health Care Organization Services data, data on pharmaceutical manufacturers' promotional efforts, data on local environmental characteristics, and data on state Medicaid and Medicare policies on coverage of antipsychotics for the period 1997-2011, we will: 1) characterize the speed of adoption of new antipsychotic medications among psychiatrists and identify factors associated with early vs. late adoption; 2) examine psychiatrists' responses to comparative effectiveness research and safety information and identify factors associated with a psychiatrist's response; and 3) evaluate whether commercial influences (e.g., manufacturer promotion) and policy factors, such as Medicaid and Medicare drug coverage restrictions, influence psychiatrists' responses to drug information. Addressing concerns about the quality and efficiency of psychopharmacologic care for people with mental disorders depends on changing the behavior of individual physicians. However, we do not know when and how to target interventions nor which interventions are most effective. Should we find that much of the variation in psychiatrists' prescribing is explained by where and when they trained then efforts to improve psychiatric residency training in psychopharmacology and evidence-based medicine should be intensified. Alternatively, if organizational factors, pharmaceutical promotion and/or policy factors explain much of the variation in prescribing behaviors, such findings would motivate interventions at the organizational and policy-level. . PUBLIC HEALTH RELEVANCE: By characterizing psychiatrist adoption of new antipsychotic medications and identifying factors that influence psychiatrist response to comparative effectiveness and safety information, such as education and training, organizational characteristics, pharmaceutical manufacturer promotion, and policy factors, this study will provide important data on how psychiatrists make prescribing decisions and respond to new clinical information. Understanding how psychiatrists adopt new medications and new evidence into their practice is critical to developing clinical and policy interventions to improve the efficiency and quality of psychiatric medication use.