Isopregnanolone, also known as isoallopregnanolone and epiallopregnanolone, as well as sepranolone (INNTooltip International Nonproprietary Name), and as 3β-hydroxy-5α-pregnan-20-one or 3β,5α-tetrahydroprogesterone (3β,5α-THP), is an endogenous neurosteroid and a natural 3β-epimer of allopregnanolone.

[1][2] It has been reported to act as a subunit-selective negative allosteric modulator of the GABAA receptor,[2] and antagonizes in animals and humans some but not all of the GABAA receptor-mediated effects of allopregnanolone, such as anesthesia,[3] sedation,[4] and reduced saccadic eye movements,[4] but not learning impairment.

[1][2] Levels of isopregnanolone, progesterone, and allopregnanolone are highly correlated across the menstrual cycle and throughout pregnancy.

[6] Isopregnanolone has a relatively long serum elimination half-life of 14 hours in humans.

[1] Isopregnanolone (developmental code name UC-1010) is under development for the treatment of premenstrual dysphoric disorder.