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Plan B is used for preventing pregnancy within 72 hours after unprotected sex. It does this by stopping ovulation or by preventing fertilization of the egg, if ovulation has already occurred. This emergency contraceptive is only approved for women of reproductive age; it is not approved for girls who have not yet had their first menstrual period. At this time, there are no off-label Plan B uses.

Plan B Uses: An Overview

Plan B One-Step™ (levonorgestrel) is the "morning-after pill," an emergency contraceptive that is used to prevent pregnancy when used within 72 hours after unprotected sex. Plan B originally came in a two-step formulation, which consisted of two tablets taken 12 hours apart. It has been replaced by the new Plan B One-Step, which consists of one tablet. Plan B One-Step is available to all women, regardless of age, without a prescription.
Plan B contains a high dose of levonorgestrel, a progesterone-type hormone that is used in many birth control pills. It prevents pregnancy primarily by stopping ovulation (the maturation and release of eggs from the ovaries) or by preventing fertilization of the egg if ovulation has already occurred. Plan B also alters the lining of the uterus (the endometrium), making it less receptive to a fertilized egg. If a fertilized egg has already implanted into the uterus, Plan B will not cause an abortion.
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. Plan B should not be used as your main form of birth control, because other methods are usually much more effective. Plan B is ideal for use in the case of contraceptive failure (when another form of birth control, such as condoms, fails) or to prevent pregnancy after sexual assault. It should not be used over and over again as a woman's primary form of birth control.
Plan B should be taken as soon as possible within 72 hours (three days) after intercourse. The sooner you can take the drug, the more effective it is at preventing pregnancy.
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Last reviewed by: Kristi Monson, PharmD;
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