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Carbamazepine and combined oral contraceptive — GPhC CRA MCQ

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ModerateDrug InteractionsCarbamazepine and combined oral contraceptiveGPhC CRA

A 26-year-old taking carbamazepine for epilepsy asks for advice after being prescribed a combined oral contraceptive by a private clinic. She wants reliable contraception. What is the most important interaction to flag?

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Correct answer: A — Carbamazepine can reduce contraceptive efficacy through enzyme induction

Carbamazepine is an enzyme-inducing antiepileptic drug that can reduce the effectiveness of hormonal contraception. The patient should be referred for suitable contraception advice, such as a method unaffected by enzyme induction. The main concern is contraceptive failure rather than acute toxicity. Barrier methods are not rendered ineffective by carbamazepine.

Reference: BNF; FSRH guidance