Why can doxycycline affect combined hormonal contraception?
Doxycycline can temporarily decrease colonic bacteria thus inhibiting the enterohepatic circulation of ethinylestradiol, the semi-synthetic oestrogen contained in all combined hormonal contraceptives. This effect can also occur with other antibiotics. There is no secondary re-absorption of progesterones via the enterohepatic circulation and therefore doxycycline (and other antibiotics) has no effect on the efficacy of progesterone-only contraceptives (including the pill, injectables, implants, the levonorgestrel releasing intrauterine system, or progesterone only emergency contraception). Therefore, this advice only applies to those taking combination contraception. Women using combined hormonal contraception (pill or patch) who are starting doxycycline should be informed that: Doxycycline may reduce the efficacy of combined hormonal contraception When starting doxycycline, additional contraceptive protection, such as condoms or abstinence, is advised for 3 weeks. If the pill free inte
