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Emergency Contraception
The used of emergency contraceptives (ECs) allows for the prevention of a pregnancy after unprotected sex or contraception failure. In the United Sates, there are currently four different methods available, including ulipristal acetate (UPA), an oral progesterone receptor agonist-antagonist; levonorgestrel (LNG), an oral progestin; off-label use of combined oral contraceptives (Yuzpe regimen); and the copper intrauterine device (Cu-IUD).

Types
UPA, a progesterone agonist-antagonist, was approved by the FDA in 2010 for use as an EC. UPA acts as a partial agonist and antagonist of the progesterone receptor and works by preventing both ovulation and fertilization. Users of UPA are likely to experience delayed menses after the expected date. In the United States, UPA is sold under the brand name Ella, which is a 30 mg single pill to be taken up to 120 hours after unprotected sex. UPA has emerged as the most effective EC pill, however, the access to UPA is very limited in US cities. UPA is a prescription emergency contraceptive pill and a recent study has found that less than 10% of pharmacies indicated that a UPA prescription could be filled immediately. 72% of pharmacies reported the ability to order UPA and the prescription to be filled in a median wait time of 24 hours.

Plan B one step was the first levonorgestrel progestin-only EC approved by the FDA in 1999. Currently, there are many different brands of levonorgestrel EC pills, including Take Action, Next Choice One Dose, and My Way and regimens include a single 1.5 mg pill of levonorgestrel. Levonorgestrel EC pills should be taken up to 72 hours after unprotected sex due to the drug becoming less effective over time. Levonorgestrel acts as an agonist of the progesterone receptor, preventing ovulation. Users of levonorgestrel often experience menses before the expected date. A prescription for levonorgestrel is not needed and can be found over the counter at local pharmacies. Because levonorgestrel does not have any life-threatening side effects, it has been approved by the FDA for use by all age groups.

The Yuzpe regimen used combination oral contraceptives for EC and has been used since 1974. This regimen is no longer commonly used due to side effects such as nausea and vomiting, as well as the discovery of more effective methods. The regimen consists of two pills, each containing a minimum 100 μg of ethinyl estradiol and a minimum of 500 μg of levonorgestrel. The first pill is taken 72 hours after unprotected sex and the second pill is taken 12 hours after the first. The Yuzpe regimen is often used in areas where dedicated EC methods are unavailable or where EC is not accepted.

The most effective form of EC is the insertion of a Cu-IUD within 5 days of unprotected sex. Because the Cu-IUD is inserted into the uterus, it has the advantage of providing continued contraception for up to 10 years. Cu-IUDs have been the only IUDs that have been approved as ECs due to the mechanism in hormonal and copper IUDs differing. Hormonal IUDs are used for the treatment of unplanned pregnancies by being placed in the uterus after an oral EC has been taken.