Progestin is a synthetic hormone similar to the naturally occurring progesterone. It has a number of pharmaceutical applications, but is most often used for either contraception or hormone replacement therapy. There are many different forms of progestin, including medroxyprogesterone, norethynodrel, and levonorgestrel.
In contraception, progestin may be paired with estrogen, while in hormone replacement therapy, it is used to balance estrogen replacement to prevent medical complications. Progestin is also used to treat disorders of the uterus including amenorrhea or the abnormal lack of menstruation, dysfunctional uterine bleeding, and endometriosis, in which cells similar to those lining the inside of the uterus grow outside the uterus, causing pain and often infertility. In addition, it can help relieve the symptoms of cancer of the endometrium, or uterine lining, the kidney, the breast, and the prostate. Progestins are also used sometimes to support the mother's hormonal output in in-vitro fertilization, and to prevent preterm birth or miscarriage in women with a history of either condition. However, progesterone is often used for such applications instead of progestin.
Progestin was created to offer the benefits of progesterone therapy without its drawbacks. When a woman is pregnant, her body releases progesterone, which prevents her from ovulating. The hormone is therefore an effective form of birth control, since it can trick the body into thinking it is pregnant and prevent ovulation. However, progesterone has low bioavailability when taken orally, meaning that the body does not absorb it well. If the hormone is injected, the problem of bioavailability is bypassed, but progesterone tends to cause irritation at the site of injection.
Progestin is much more effective than progesterone when taken orally. The first progestin, ethisterone, was synthesized in 1938 by Hans Herloff Inhoffen, and many other versions were to follow. The first oral contraceptive, Enovid, contained norethynodrel as its active ingredient. It was approved as a contraceptive by the United States in 1960, and by the United Kingdom a year later. Before 1960, Enovid and similar hormonal treatments were used only for menstrual disorders.
In hormone replacement therapy, which alleviates symptoms associated with the body's diminished hormonal output during menopause, progestins are used to balance estrogen replacement. If estrogen is used on its own, complications including abnormal proliferation of the endometrial cells, a condition called endometrial hyperplasia, can result. If untreated, it can lead to endometrial cancer.