context: Emergency contraception -- also called postcoital contraception -- is a form of birth control that may be used by women who have had unprotected sex or used a birth control method that failed. The treatment generally is reserved for specific situations and is not a regular method of birth control. Emergencies include being raped, having a condom break or slip off during sex, or missing two or more birth control pills during a monthly cycle. Emergency oral contraception is used to prevent a pregnancy, not end one. They work primarily by delaying ovulation. Emergency contraception does not protect against sexually transmitted diseases. It is not RU-466, the medication used to induce abortions. There are 2 types of emergency contraception: Pill form IUD There are 3 types of emergency contraception in pill form that are sold both with and without a prescription. You need to be 17 to buy them if a prescription is needed. Depending on the brand and dose, you might get 1 pill or 2. Pills containing a hormone called levonorgestrel: My Way (over-the-counter) Plan B One- Step (over-the-counter) Preventeza (over-the-counter) Take Action (over-the-counter) Birth control pills can also be used as emergency contraception, but you have to take more than one pill at a time to keep from getting pregnant. This approach works, but it is less effective and more likely to cause nausea than levonorgestrel. Birth control pills require a prescription. Talk to your doctor or nurse to make sure you are taking the correct pills and dose. A third kind of emergency contraception pill is called ulipristal (ella, ella One). You need a prescription to get it. Levonorgestrel is a specifically packaged emergency contraception. It is available to anyone over the counter without a prescription or age restrictions. Ella is a non-hormonal pill. It contains ulipristal, a non-hormonal drug that blocks the effects of key hormones necessary for conception. It is available only by prescription. Levonorgestrel emergency contraception may prevent pregnancy by temporarily blocking eggs from being released, by stopping fertilization, or by keeping a fertilized egg from becoming implanted in the uterus. Levonorgestrel is taken in one dose with one pill. Its effectiveness depends on how soon you take the pill. It should be taken as soon as possible -- within 72 hours of unprotected intercourse. When Levonorgestrel is taken as directed, it can reduce the chance of pregnancy by close to 90%. Ella can be taken up to 120 hours after sex. It is taken as one tablet in one dose. An IUD can be inserted to prevent pregnancy. The device works by stopping implantation of a fertilized egg in the uterus and must be placed within 5 days of having unprotected intercourse. If levonorgestrel is taken as directed after unprotected sex, it will decrease the chances of a pregnancy occurring. About 7 out of every 8 women who would have gotten pregnant do not become pregnant. However, research shows that levonorgestrel starts to lose its effectiveness in women who are overweight or obese. Instead, an IUD is the suggested option in this group. In two reported studies, Ella significantly reduced the pregnancy rate from an expected rate of 5.5% and 5.6% to 2.2% and 1.9%, respectively. In a pooled analysis of the data, the effectiveness did not fade for 120 hours after unprotected sex. An IUD can be up to 99% effective when inserted within 5 to 7 days after unprotected intercourse. Emergency contraceptive pills ( ECPs) are available at Planned Parenthood; college, public, and women's health centers; private doctors; and some hospital emergency rooms. Some doctors will prescribe ECPs over the phone and call the prescription in to a pharmacy. As mentioned above, levonorgestrel is available at pharmacies without a prescription. Levonorgestrel will not affect an implanted pregnancy. Ella should not be used by women who are already pregnant or may be pregnant. The risk to a human fetus is unknown. Animal studies have demonstrated risk of fetal loss. Women who have a chronic medical condition should check with their doctor or health care provider before using this method of emergency contraception. The most common side effects associated with emergency contraception pills include: Nausea Abdominal pain Fatigue Headache Menstrual changes Ask your doctor or pharmacist about ways to reduce nausea. They may prescribe some anti-nausea medicine for you to take before you take an ECP. No. Emergency contraception will not protect you from contracting an STD, such as HIV, the virus that causes AIDS. The best way to avoid getting STDs is to limit sexual contact to one uninfected partner. If that is not an option, use a latex condom correctly every time you have sex.