This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'A woman who has been taking oral contraceptives for several years is diagnosed with epilepsy and started on phenytoin. Which of the following is the most likely consequences of adding phenytoin? \nSelect and explain. \nA. Agranulocytosis, B. Phenytoin toxicity, C. Reduced contraceptive efficacy, D. Thromboembolism', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]