Answer
It does not usually reduce hormonal contraceptive effectiveness, but oestrogen-containing products may lower valproate concentrations. Vomiting or severe diarrhoea may also make oral contraception less reliable.
Sources for this answer
- Episenta 150mg Prolonged Release Capsules — Current selected SmPCemc · Summary of Product Characteristics
- NHSNHS · NHS medicine guidance
General medicine information. Follow the instructions for your own medicine and speak to a pharmacist or clinician about your individual circumstances.