Wikipedia
Epipregnanolone, also known as 3β-Hydoxy-5β-pregnan-20-one or 3β,5β-tetrahydroprogesterone (3β,5β-THP), is an endogenous neurosteroid. It acts as a negative allosteric modulator of the GABA receptor and reverses the effects of potentiators like allopregnanolone. Epipregnanolone is biosynthesized from progesterone by the actions of 5β-reductase and 3β-hydroxysteroid dehydrogenase, with 5β-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 receptor, and also acts as a TRPM3 channel activator.