How does the morning after pill work?

There are two types of hormonal emergency contraception pills (morning after pill), ulipristal acetate (sold as ellaOne) and levonorgestrel (sold as generic levonorgestrel or Levonelle).

Levonorgestrel has to be taken within 72 hours (3 days) of sex, and ulipristal acetate has to be taken within 120 hours (5 days) of sex.

Both pills work by preventing or delaying ovulation (release of an egg). Emergency contraception is best taken as soon as possible to be effective.

Emergency hormonal contraception is only effective if taken before you ovulate and will not protect you against pregnancy during the rest of your menstrual cycle.

Ulipristal acetate (ellaOne) is slightly more effective than Levonorgestrel at preventing pregnancy but it may also prevent other types of hormonal contraception from working for a week after use.