BACKGROUND: There is evidence that pharmacist interventions improve clinical outcomes. The few studies that address economic outcomes (a) often report estimated instead of actual medical costs, (b) report only medication costs, or (c) have been conducted in settings that are not typical of community-based primary care.OBJECTIVES: To (a) determine whether a clinical pharmacist's recommendations to physicians regarding optimizing medication therapy are related to medical costs in capitated patients in an internal medicine practice, and (b) compare what primary care physicians (PCPs) in a comparison group actually did proactively to optimize medication therapy versus what a clinical pharmacist would have recommended to them.METHODS: This was a prospective, controlled study comparing 2 internal medicine practices. Study enrollment was performed using a screening process carried out every 1-2 weeks on a rolling basis for 1 year from July 2001 through June 2002. Eligibility criteria for prospective enrollment were (a) 1 or more risk factors: at least 1 chronic disease or an event (e.g., emergency room visit, adverse drug reaction, medication nonadherence) or aged 50 years or older, (b) a scheduled visit to see a PCP within 2 weeks from the screening date or a diagnosis of diabetes without a PCP visit during the first 6 months of the study, (c) need for optimization of medication therapy as determined by a clinical pharmacist on the screening date, and (d) 12 months of continuous insurance eligibility before enrollment in the study. For inclusion in the final study analyses, patients were also required to have continuous insurance eligibility through 12 months from study enrollment. One clinical pharmacist made recommendations to optimize medication therapy in the intervention group. For the comparison group, the same pharmacist proposed recommendations that remained concealed from the physicians. The primary outcome measure was per patient per year (PPPY) medical cost, based on plan liability (gross allow able costs minus patient costs), excluding prescription drug cost. Additional outcome measures included numbers of outpatient visits, hospital admissions, emergency room (ER) visits per 1,000 patients, and hospital days; and percent of recommendations that were accepted by the PCPs. Changes in outcome measures from the pre-intervention to postintervention period were compared across study groups in a difference-indifference analysis, using the Student's t-test for normally distributed data and the Mann-Whitney U-test (nonparametric) for skewed data.RESULTS: There were 127 and 216 adult patients in the intervention and comparison groups, respectively. The primary outcome, change in mean PPPY medical (excluding pharmacy) cost, did not differ significantly between the groups (P = 0.711). The between-group difference in the change in ER visits per 1,000 patients approached statistical significance (P = 0.054). Intervention group patients were more likely than comparison group patients to have the following issues...