How effective is emergency contraception at preventing pregnancy?

The effectiveness of emergency contraception (EC) depends on what type you use, how soon you take it after having sex, and how much you weigh

If you’re taking over-the-counter EC pills, like Plan B One-Step, Next Choice, or other generics, the sooner you take it after sex, the more effective it is. We repeat: the sooner, the better. You can take it for up to 5 days, but within 3 days is more effective. (You can even get some to have on hand so you have it when you need it.) Over-the-counter EC pills are less effective if you weigh more than 165 pounds, and unfortunately, research shows that taking more than one at a time doesn’t work.

If you’re taking the prescription EC pill, brand name ella, you can take it up to 5 days after sex. Unlike over-the-counter EC pills, it’s as effective on day five as it is on day one. Prescription EC is less effective if you weigh more than 195 pounds.

Getting some types of IUD placed within five days after sex is the most effective method of EC, no matter how much you weigh.