Study pharmacists reviewed patient-reported medication symptoms and carried out chart reviews to screen for possible ADEs, defined as an injury related to use of a drug. Two board-certified internists reviewed each screened event independently using interviews, chart reviews, and medication references to determine the likelihood that the event identified by patient report or chart review was in fact an injury and was related to the use of a medication (and hence an ADE). Differences were resolved by discussion. Events were judged to be ADEs if the confidence level of the consensus judgment was 4 or greater on a 6-point scale, signifying greater than 50% certainty that an ADE had occurred. The ADEs were classified by level of severity (ie, life-threatening, serious, or significant) and as nonpreventable, preventable, or ameliorable. Serious events affected end-organ function and produced symptoms that required timely medical evaluation or treatment, such as sexual dysfunction, symptomatic hypotension, and gastrointestinal bleeding. Significant events, in contrast, caused symptoms that were more often annoying or uncomfortable but were judged less dangerous, such as dyspepsia, dizziness, cough, insomnia, or rash. Preventable events were defined as those attributable to errors that could have been avoided entirely given what was known at the time. An example of a serious preventable ADE was an allergic rash in a patient for whom an antibiotic had been prescribed despite a documented allergy. Ameliorable ADEs were defined as those in which the severity or duration could have been reduced substantially had different actions been taken.12,13 An example of a serious ameliorable ADE was months of sexual dysfunction in a patient whose physician failed to discontinue treatment with a selective serotonin reuptake inhibitor after the patient reported the adverse effect of the drug. We assumed that preventable and ameliorable ADEs could result from decisions of either physicians or patients and asked reviewers to identify the party whose behavior (action or inaction) was most responsible for the event. Interrater agreement (determined before consensus) for the presence of ADEs (κ = 0.89), severity (κ = 0.72), and preventability or ameliorability (κ = 0.70) was high.