A 44-year-old woman accidentally ingested phenelzine along with venlafaxine. Thirty minutes after the ingestion the woman began to feel nauseous and anxious. Approximately 45 minutes later a friend noted that the woman had lower extremity shaking and increasingly rapid respirations. The friend brought the woman to the emergency department and she was subsequently diagnosed with serotonin syndrome. Serotonin syndrome is usually precipitated by combinations of serotonin-potentiating agents and can lead to devastating outcomes. When using combinations of drugs that elevate serotonin levels in the central nervous system, the possibility of serotonin syndrome should be considered.