<unk> (P4) is a medication and naturally occurring steroid hormone. It is a progestogen and is used in combination with estrogens mainly in hormone therapy for menopausal symptoms and low sex hormone levels in women. It is also used in women to support pregnancy and fertility and to treat gynecological disorders.<unk> can be taken by mouth, in through the vagina, and by injection into muscle or fat, among other routes. A<unk> vaginal ring and<unk> intrauterine device used for birth control also exist in some areas of the world.<unk> is well tolerated and often produces few or no side effects. However, a number of side effects are possible, for instance mood changes. If<unk> is taken by mouth or at high doses, certain central side effects including sedation, sleepiness, and cognitive impairment can also occur. The medication is a naturally occurring progestogen and hence is an agonist of the<unk> receptor (PR), the biological target of progestogens like endogenous<unk>  It opposes the effects of estrogens in various parts of the body like the uterus and also blocks the effects of the hormone aldosterone. In addition,<unk> has neurosteroid effects in the brain.<unk> was first isolated in pure form in 1934. It first became available as a medication later that year. Oral micronized<unk> (OMP), which allowed<unk> to be taken by mouth, was introduced in 1980. A large number of synthetic progestogens, or progestins, have been derived from<unk> and are used as medications as well. Examples include medroxyprogesterone acetate and norethisterone. In 2019, it was the 188th most commonly prescribed medication in the United States, with more than 3million prescriptions.
Progesterone 
Estrogen 
Estrogen
Androgen
Estradiol 
Estradiol
Methyltestosterone
Progestogen