A 27-year-old primigravid woman brings her 3-month-old son to the clinic for evaluation. She did not receive prenatal care during pregnancy and reports that she had been taking an unspecified medication for mood swings while pregnant. The infant was born cyanotic and was found to have a congenital heart defect characterized by apical displacement of the septum and posterior tricuspid valve leaflets. A chest radiograph is obtained. Which of the following medications was the mother most likely taking during pregnancy?