Both breakthrough bleeding and contraceptive failure have been seen in women taking
St John's wort (Hypericum perforatum). In two cases the failure of emergency hormonal contraception has been attributed to the use of St John's wort.
Since it is not known who is particularly likely to be at risk, women taking hormonal
contraceptives should either avoid St John's wort (the recommendation of the CSM in the UK) or they should use an additional form of contraception. For general advice on the use of
enzyme inducers, such as St John's wort, and
contraceptives, see
contraceptives.