Progestagens (also spelled progestogens or gestagens) are hormones similar in effect to progesterone, the only natural progestagen. All other progestagens are synthetic and are often referred to as progestins.

All progestagens have antiestrogenic (counteracting the effects of estrogens on the body) and antigonadotropic (inhibiting the production of sex steroids by gonads) properties.

Progestagens differ in their potency (affinity for progesterone receptors) and side-effects. Such side-effects may be androgenic (medroxyprogesterone and most C19 progestagens), antiandrogenic (cyproterone acetate), estrogenic, glucocorticoid (some C21 progestagens) or antimineralocorticoid (progesterone).

Most progestagens are used for their antiestrogenic properties in oral contraceptives to avoid overstimulation of the endometrium which could lead to endometriosis. Medroxyprogesterone acetate (brand name Depo Provera) is used in birth control. Cyproterone is used mostly as an antiandrogen.