It depends on what you mean by “just,” and it depends on what you mean by “sex.” If a girl had unprotected vaginal sex with a guy in the last five days, she can take emergency contraception (EC). Until recently, a girl or woman had to take EC within 72 hours of unprotected sex, so you might still see 72 hours noted on the packaging, but now five days or fewer is the recommendation. Try to take it as soon as possible after unprotected sex, though, as this may increase the chance that it will prevent pregnancy.

EC is basically a high dose of certain types of birth control pills. The current brand names for EC in the U.S. are Plan B One-Step, Ella and Next Choice. Plan B One Step and Ella require that you take one pill. Next Choice requires you to take two pills, 12 hours apart. Read the instructions on your package to be sure you are taking the medication properly.

EC is not an abortion; it works by preventing pregnancy before it happens. It will not end a pregnancy that has already started. This is why it’s so important to take it as soon as possible after unprotected sex. Unprotected sex includes not using any method of birth control or condoms, or having a method fail (like a condom breaking).

If you are 17 or older, you can get Plan B One Step and Next Choice directly from a pharmacist without a prescription in all 50 states and Washington, D.C. The newly approved EC pill, Ella, is only available to anyone of any age with a prescription.

If you need a prescription for EC, you can find a health care provider near you, as well as answers to your questions about EC, at NOT-2-LATE.com, the Emergency Contraception Web site.

Remember that you must take the first dose of EC within five days of unprotected sex.

The sooner a girl takes EC, the better. So the closer she takes it to the actual time of unprotected sex, the better. It can reduce the chance of a pregnancy by up to 89 percent.

As with any birth control pills, there are some possible side effects to taking EC. Some girls experience side effects, but many don’t experience any at all. The most common side effects are nausea, pain in the lower abdomen, changes in the menstrual cycle, headache, fatigue and dizziness.

EC provides no protection against HIV or other STDs. And if a couple had unprotected sex, either or both partners could be at risk for an STD. Anyone who has unprotected sex should get tested for STDs.

Find a clinic that provides EC, STD testing and other sexual health services.