General practitioners are key stakeholders in good prescribing practices. More than half of patients have at least one unintended medication discrepancy upon hospital admission, some of which have the potential to cause severe discomfort or clinical deterioration. We report a case of a drug mistakenly administered to a 66-year-old man with cirrhosis and chronic alcoholism. Based on his regular prescription, he received 1 g/day of valproate during a hospitalization for cardiac valve surgery. This anticonvulsant was initially prescribed by his general practitioner for his epileptic dog and has been added to his own prescription to be covered by the French national health insurance. The aim of this article is to emphasize that general practitioners, physicians, and pharmacists have a major role to play in preventing the diversion of prescription drugs and limiting the risk of adverse drug events.