A 57-year-old woman with a history of depression and insomnia presented to the emergency department with a 3-day history of shortness of breath and dizziness. The physical examination was notable for pallor. Laboratory studies showed a hemoglobin level of 4.4 g per deciliter (reference range, 11.6 to 15.5), an elevated reticulocyte count, an elevated lactate dehydrogenase level, and a low haptoglobin level. The results of hemoglobin electrophoresis and glucose-6-phosphate dehydrogenase testing were normal, and methemoglobin and direct antiglobulin tests were negative. A peripheral-blood smear (Panel A, Giemsa staining) showed poikilocytosis, nucleated red cells (black arrows), and polychromatic cells (white arrows). The findings were also consistent with oxidative hemolysis, including the presence of bite cells (Panel A, red arrows), blister cells (Panel A, asterisks), and erythrocyte inclusions (Panel B, Giemsa staining). The erythrocyte inclusions were identified as Heinz bodies on the basis of positive staining with methyl violet (Panel C). Blood transfusions were administered. After a prolonged toxicologic investigation that involved multiple readmissions over the course of the next 7 months, the patient eventually reported having taken 10 times the recommended daily dose of zopiclone (a nonbenzodiazepine hypnotic) every night to treat insomnia since 1 month before the first presentation. Urine drug testing was positive for zopiclone. A diagnosis of drug-induced oxidative hemolysis was made. The patient was counseled to cease zopiclone use and was referred to psychiatry for treatment.