Post coital or “emergency” contraceptive pills such as Plan B (levonorgestrel) work by disrupting the menstrual cycle. Depending when in the cycle they are taken, they may prevent ovulation, fertilization, or implantation. These mechanisms have different halachic implications: preventing ovulation is the least problematic, preventing implantation of a fertilized embryo is the most problematic. For both medical and halachic reasons, they should never be used as a routine contraceptive method.

However, in cases that truly are an emergency, there is room to permit them, since it is uncertain whether conception has taken place at all. Furthermore, even if conception has occurred, this would be a very early abortion which is easier to permit halachically under extenuating circumstances. Our site’s rabbinic supervisor, Rav Yehuda Henkin, permits the use of emergency contraceptive pills as intended – within a few days of possible conception – without further consultation.

A woman who wishes to consult her own rabbi needs to ask as quickly as possible, since Plan B works only if taken within 72 hours after relations – and is more likely to be effective the sooner it is taken.

In the case of sexual assault, emergency contraception is permitted.