Complications resulting from medications, or adverse drug events (ADEs), are prevalent and are a major source of excess morbidity and costs. ADEs are particularly problematic in older patients because of their higher burden of comorbidity and diminished physiologic reserve. In addition, older patients are more likely to be exposed to polypharmacy, a major risk factor for ADEs. While ADEs may be idiosyncratic, many result from medical errors and inadequate systems for ensuring the safe and effective use of medications.