<unk>  is a hormonal medication which is used in a number of birth control methods. It is combined with an estrogen to make combination birth control pills. As an emergency birth control, sold under the brand name Plan B among others, it is useful within 72 hours. This should not be confused with EllaOne which can be effective within 120 hours (5 days) of unprotected sex. The more time that has passed since sex, the less effective the medication becomes, and it does not work after pregnancy (implantation) has occurred. It decreases the chances of pregnancy by 57 to 93%. In an intrauterine device (IUD), such as Mirena among others, it is effective for the long-term prevention of pregnancy. A<unk> -releasing implant is also available in some countries. Common side effects include nausea, breast tenderness, headaches, and increased, decreased, or irregular menstrual bleeding. When used as an emergency contraceptive, if pregnancy occurs, there is no evidence that its use harms the baby. It is safe to use during breastfeeding. Birth control that contains<unk>  will not change the risk of sexually transmitted infections. It is a progestin and has effects similar to those of the hormone progesterone. It works primarily by preventing ovulation and closing off the cervix to prevent the passage of sperm.<unk>  was patented in 1960 and introduced for medical use together with ethinylestradiol in 1970. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In the United States,<unk> -containing emergency contraceptives are available over the counter (OTC) for all ages. In 2016, it was the 223rd most commonly prescribed medication in the United States, with more than two million prescriptions.
Levonorgestrel
Etonogestrel
Norgestrel
Desogestrel
Chloroethynylnorgestrel
Gestodene
5α-Dihydrolevonorgestrel
Norelgestromin