Epipregnanolone, also known as 3ò-hydroxy-5ò-pregnan-20-one, 3ò,5ò-tetrahydroprogesterone, or 3ò,5ò-THP, is an endogenous neurosteroid. It acts as a negative allosteric modulator of the GABA<sub>A</sub> receptor and reverses the effects of potentiators like allopregnanolone. Epipregnanolone is biosynthesized from progesterone by the actions of 5ò-reductase and 3ò-hydroxysteroid dehydrogenase, with 5ò-dihydroprogesterone as the intermediate in this two-step transformation.
Epipregnanolone is not a progestogen itself, but via metabolization into other steroids, behaves indirectly as one.
The sulfate of epipreganolone, epipregnanolone sulfate, is a negative allosteric modulator of the NMDA and GABA<sub>A</sub> receptors and also acts as a TRPM3 channel activator.