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

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EasyDrug InteractionsSt John's wort and oral contraceptiveGPhC CRA

A patient using a combined oral contraceptive wants to buy St John's wort for low mood. She has not spoken to her GP about her symptoms. What is the most important interaction to flag?

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Correct answer: A — St John's wort can reduce contraceptive effectiveness

St John's wort induces drug-metabolising enzymes and can reduce the effectiveness of hormonal contraception. It also has important interactions with many other medicines and should not be treated as a harmless supplement. Low mood should be assessed appropriately, especially if persistent or associated with risk features. The interaction increases risk of contraceptive failure.

Reference: BNF