<unk> s, also sometimes written<unk> s or gestagens, are a class of natural or synthetic steroid hormones that bind to and activate the progesterone receptor (PR). Progesterone is the major and most important<unk>  in the body. The<unk> s are named for their function in maintaining pregnancy (i.e., progestational), although they are also present at other phases of the estrous and menstrual cycles. The<unk> s are one of three types of sex hormones, the others being estrogens like estradiol and androgens/anabolic steroids like testosterone. In addition, they are one of the five major classes of steroid hormones, the others being the androgens, estrogens, glucocorticoids, and mineralocorticoids, as well as the neurosteroids. All endogenous<unk> s are characterized by their basic 21-carbon skeleton, called a pregnane skeleton (C21). In similar manner, the estrogens possess an estrane skeleton (C18), and androgens, an androstane skeleton (C19). The terms progesterone,<unk> , and progestin are mistakenly used interchangeably both in the scientific literature and in clinical settings. Progestins are synthetic<unk> s and are used in medicine. Major examples of progestins include the 17α-hydroxyprogesterone derivative medroxyprogesterone acetate and the 19-nortestosterone derivative norethisterone. The progestins are structural analogues of progesterone and have<unk> ic activity similarly, but differ from progesterone in their pharmacological properties in various ways. In addition to their roles as natural hormones,<unk> s are used as medications, for instance in menopausal hormone therapy and transgender hormone therapy for transgender women; for information on<unk> s as medications, see the progesterone (medication) and<unk>  (medication) articles.
Progestogen
Norgesterone
Antigonadotropin
Catechol estrogen
Androgen
Haloprogesterone
Vinyltestosterone
Androstenediol