3ò-Dihydroprogesterone (3ò-DHP), also known as 3ò-hydroxyprogesterone, or pregn-4-en-3ò-ol-20-one (4-pregnenolone, ô<sup>4</sup>-pregnenolone), is an endogenous steroid. It is biosynthesized by 3ò-hydroxysteroid dehydrogenase from progesterone. Unlike 3ñ-dihydroprogesterone (3ñ-DHP), 3ò-DHP does not act as a positive allosteric modulator of the GABA<sub>A</sub> receptor, which is in accordance with the fact that other 3ò-hydroxylated progesterone metabolites such as isopregnanolone and epipregnanolone similarly do not act as potentiators of this receptor and instead inhibit it as well as reverse the effects of potentiators like allopregnanolone. 3ò-DHP has been reported to possess about the same potency as progesterone in a bioassay of progestogenic activity, whereas 3ñ-DHP was not assessed.