<unk>  is a medication which is used as a means of birth control for women. It is available as an implant placed under the skin of the upper arm under the brand names Nexplanon and Implanon, and in combination with ethinylestradiol, an estrogen, as a vaginal ring under the brand names NuvaRing and Circlet.<unk>  is effective as a means of birth control within 8 hours of insertion and lasts at least three or four years with some data showing effectiveness for five years. Following removal, fertility quickly returns. Side effects of<unk>  include menstrual irregularities, breast tenderness, mood changes, acne, headaches, vaginitis, and others.<unk>  is a progestin, or a synthetic progestogen, and hence is an agonist of the progesterone receptor, the biological target of progestogens like progesterone. It works by stopping ovulation, thickening the mucus around the opening of the cervix, and altering the lining of the uterus. It has very weak androgenic and glucocorticoid activity and no other important hormonal activity.<unk>  was patented in 1972 and introduced for medical use in 1998. It became available in the United States in 2006.<unk>  implants are approved in more than 90 countries and used by about three million women globally as of 2010. A closely related and more widely known and used progestin, desogestrel, is a prodrug of<unk>  in the body.
Etonogestrel
Levonorgestrel
Gestodene
Desogestrel
Norgestrel
Chloroethynylnorgestrel
5α-Dihydrolevonorgestrel
Hexestrol