text: 20β-Dihydroprogesterone (20β-DHP), also known as 20β-hydroxyprogesterone (20β-OHP), is an endogenous metabolite of progesterone which is formed by 20β-hydroxysteroid dehydrogenase (20β-HSD). It is a progestogen similarly to progesterone, with about 20 to 50% of the progestogenic activity of progesterone. It can be converted by 20β-HSD into progesterone in the uterus. The effects of 20β-HSD on the uterus, mammary glands, and in maintaining pregnancy have been studied. The progestogenic activity of 20β-HSD has also been characterized in women.