What if plan b does not work?

Options: Then you have to think about the possibility of being pregnant and figure out what options are available to you.

It should not harm: fetus. Plan B One-Step is up to 89 % effective when taken within 72 hours (3 days) after unprotected sex. It can reduce chance of pregnancy by up to 95% if used within 24 hours. It continues to reduce the risk of pregnancy up to 120 hours (5 days) after unprotected sex, but is less effective as time passes.

Yes: Plan b is about 90% effective if taken within 3 days (72 hours) of having unprotected sex. It may still work up to 5 days (120 hours) after unprotected sex, but the failure rate is higher.

Plan B can work: Plan B pills contain a high dose of the active ingredient Levonorgestrel, which is a second generation progestin. Progestins, just like natural Progesterone cause the uterine endometrium to slough thus causing a period. It works mainly by stopping the release of an egg from the ovary. It is possible that it may also work by preventing fertilization of an egg and its attachment to the uterus.