A 24-year-old woman with a history of major depressive disorder treated with sertraline is brought to the emergency department by her partner for evaluation of fever, vomiting, and weakness. In the emergency department, her temperature is 103°F, her heart rate is 129 beats per minute, she is agitated and restless, and she displays hyperactive reflexes. Her symptoms began several hours after she used a new medication prescribed by her primary care provider. Which of the following is most likely to be the new medication?