Women taking both St. John's wort and
oral contraception report an increase in irregular bleeding and, much more alarming, an uptick in unplanned pregnancies.
According to the consent data, 56.2 % of the women
reported that a method of birth control had been used but had failed (90.3 %
reported condom failure, 7.9 % erratic
oral contraceptive use and 1.8 % other forms of
contraception failure).