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St John's wort and oral contraception — GPhC CRA MCQ

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ModerateDrug InteractionsSt John's wort and oral contraceptionGPhC CRA

A 25-year-old woman taking a combined oral contraceptive asks to buy St John's wort for low mood. She takes no prescribed antidepressant and has no immediate mental health crisis. She asks whether herbal products interact with contraception. What is the most important interaction to flag?

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Correct answer: C — St John's wort may reduce contraceptive effectiveness

St John's wort induces drug-metabolising enzymes and can reduce the effectiveness of hormonal contraception. It can also interact with many medicines, including antidepressants. The patient should be advised not to use it with the combined pill and to seek appropriate support for low mood. Barrier methods are not made ineffective by St John's wort.

Reference: BNF St John's wort interactions; FSRH guidance