You should always take ECPs as soon as you can after having unprotected sex.  About 7 out of 8 women who would have gotten pregnant do not become pregnant if emergency contraceptive pills are taken within 72 hours, and some types of ECPs may work up to 5 days (120 hours) after sex. An alternative emergency contraception relies on insertion of a copper-releaseing intrauterine device (IUD) within 5 days after unprotected sex.

When used correctly, emergency contraceptive pills (ECPs) work very well at preventing pregnancy.  Of the 8 out of 100 women who would become pregnant from unprotected sex, 1% who take progestin-only ECPs (like Plan B) will become pregnant, while 2% who take ECPs with estrogen and progestin will become pregnant.  The IUD works even better, with only about 0.1% becoming pregnant.

Some women feel sick and throw up after taking ECPs. Headache, cramps, and fatigue also can occur. Progestin-only ECPs cause fewer side effects than combined pills that also contain estrogen. If you throw up after taking ECPs, call your doctor or pharmacist.

IUD placement has risks of pelvic infection or harming the uterus, but these risks are quite rare.

You can get Plan B at drugstores and stores with a licensed pharmacist. The FDA recently approved Plan B for sale without a prescription to 17-year-olds. Women and men must show proof of age to buy Plan B. If you are younger than 17 and need emergency contraception, you will need a prescription, so act quickly. Talk to your parents, your doctor, or visit a family planning clinic and ask for help.