Used widely in contraceptions and in hormone replacement therapy during menopause, progestins affect a lot more than just the uterus.
Progestins are a synthetic version of the naturally-occurring female reproductive hormone progesterone. The compounds were initially designed to counteract certain unwanted effects of estrogen in reproductive tissues, particularly in the uterus. Several generations of progestins have been developed both for use in contraception and in hormone replacement therapy during menopause, and they continue to evolve.
While the target of progestins used in hormone therapy is generally the uterus, progestin therapy affects every major organ system including the brain, the cardiovascular system, the immune system and the generation of blood cells. As in other systems, progestins have unique effects on the brain which ultimately could impact the long-term neurological health of users. Most of the effects of progestins on the brain are beneficial, although some research has shown that they may pose some risks.

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When used as contraceptives, progestins work by preventing ovulation and pregnancy and a table at the end of this article lists the brands currently on the market. They are often combined with estrogen to attain better control of the menstrual cycle -- and to inhibit the maturation of the (young egg cell) more effectively -- as well as discourage ovulation. The majority of contraceptive drugs currently on the market contain estrogen and progestin in combination. Other formulations of hormones, including administration by injection, implants, vaginal rings, transdermal gels, and sprays have also been used for contraception. One of the most common uses of hormone therapy is, of course, to treat menopausal and perimenopausal symptoms that develop from the natural decline of the female reproductive hormones.