Many millions of dollars have been spent on preventing adverse drug reactions at the point of prescribing. Automated systems help identify drug-drug interactions and excessive drug doses. Computerized alerts warn prescribers about potentially inappropriate drugs in older adults. However, only one-quarter of adverse drug reactions can be prevented by catching errors or problems at the time of prescribing.1 The remainder of adverse drug reactions are not the result of prescriber error but simply represent the known adverse effects of drugs. Some patients who take calcium channel blockers will develop peripheral edema. Some patients who take selective serotonin reuptake inhibitors will experience marked sexual dysfunction. For some drugs, risk factors have been identified that place a patient at higher risk of developing an adverse event. However, in most cases, we cannot predict who will develop an adverse drug reaction and who will not. We prescribe and hope for the best.