This prospective cohort study evaluated more than 1200 outpatient prescriptions, surveyed patients, and conducted a chart review during a 4-week period. Investigators discovered that 25% of patients experienced an adverse drug event with selective serotonin-reuptake inhibitors, beta blockers, angiotensin-converting-enzyme inhibitors, and nonsteroidal anti-inflammatory medication classes the most frequently implicated. The rate of ADEs in this study approached 27 per 100 patients, a rate that quadruples those estimated in the inpatient setting. The authors suggest a number of preventive strategies that may reduce the nearly one third of events that were deemed preventable.