The pharmacologist Stephen Piscitelli from the National Institues of Health in the U.S. warns against possible adverse effect of taking contraceptive pills and St. John's wort at the same time. St. John's wort has become popular as an alternative antidepressant drug.
He recently observed to the medical journal The Lancet that up to 50% of the effect of certain drugs can be abolished if the person also uses St. John's wort. Many women who take contraceptive pills and also use St. John's wort report of spotting and some of them have even become pregnant.
It is believed that St. John's wort can reduce the effect of several drugs, e.g. certain types of heart medicine, one type of HIV medicine (Indinavir), Cyclosporine (a vital medicine that prevents the rejection of transplanted organs), certain types of chemotherapy, and contraceptive pills.
The theory is that St. John's wort is metabolized in the same way as other types of drugs - i.e. in the liver, and that the turnover capacity of the liver is thereby exhausted. This will result in the prescription drugs not being quite so effective.
However, there are large variations. Some studies have shown that there was not much interaction between St. John's wort and other kinds of drugs while other studies have shown that indeed there is some kind of interaction. This might be due to the absorbability of St. John's wort or different interpersonal biochemistry.
The health authorities in the U.S. have warned against using St. John's wort while taking some other kind of medicine until further studies have been carried out. Using St. John's wort while taking contraceptive pills is certainly deprecated.
The article does not comment on the possibility of prescription antidepressants being able to counteract the effect of contraceptive pills although antidepressants are also metabolized by the liver.
