The Swedish Medical Products Agency has issued a warning that St John's Wort, a herbal extract, could counteract the effect of oral contraceptives.

The pharmaceutical regulator has previously issued warnings saying that natural remedies containing St John's Wort may have an effect on several drugs, including hormone-based contraceptives, HIV medicines, blood-thickening drugs and cyclosporine, a drug used to prevent rejection of organ transplants.

The new warning comes after two Swedish women were reported to have had unwanted pregnancies because they took St. John's Wort at the same time as the contraceptive pill.

　　From Healthy.net