Interactions with hormonal contraception.

All methods of contraception have failure rates. Additional failures may occur when interacting drugs are used, and knowledge of these mechanisms should help minimise such problems. This article will look at interactions with hormonal methods of contraception, only some of which, at the present state of knowledge, have clinical significance. The synthetic hormones ethinyloestradiol (EE) and progestogens are absorbed (if taken orally), transported to the liver, metabolised, and returned to the large bowel. Progestogen is excreted, whereas oestrogen is reabsorbed (the enterohepatic circulation, EHC).