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Effects of Plan B

Taking it within 72 hours after unprotected sex reduces the risk of pregnancy by 89 percent. After any one act of unprotected intercourse, the average woman has an 8 percent chance of getting pregnant. If she takes Plan B, that risk is reduced to about 1 percent.

When and How to Use It

Some general considerations for when and how to use Plan B include the following:
  • The older version of Plan B (as well as the generic version) came in a pack with two tablets. The first one is taken right away within 72 hours of unprotected sex, and the second one is taken 12 hours later, even if this means taking it in the middle of the night.
  • The newer Plan B One-Step comes in a pack with just one tablet and is taken as a single dose. 
  • The sooner it is taken, the more effective it is at preventing pregnancy.
  • While it is not necessary to take it with food, doing so can help prevent stomach upset.
  • If you vomit within one hour of taking a dose of Plan B, call your healthcare provider immediately to see if you should repeat the dose.
  • For the medication to work properly, it must be taken as prescribed.

Dosing Information

There is only one standard dosage for Plan B, regardless of your age or weight. As always, do not adjust your dose unless your healthcare provider specifically tells you to do so.
(Click Plan B Dosage for more information.)
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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