Answer
Yes, St John's wort can reduce Marvelon's contraceptive effectiveness by inducing enzymes that increase sex hormone clearance; use an additional barrier contraceptive during St John's wort use and for 28 days after stopping it.
Sources for this answer
- MarvelonOrganon Pharma (UK) Limited · emc · SmPC §4.5 Interaction with other medicinal products · Version 18Document updated
Sources checked