R,5 R,8 R,9 S,10 S,13 S,14 S,17 S)-3-hydroxy-10,13-dimethyl-2,3,4,5,6,7,8,9,11,12,14,15,16,17-tetradecahydro-1 H-cyclopenta[ a]phenanthren-17-yl]ethanone
Eltanolone; 5β-Pregnan-3α-ol-20-one; 3α-Hydroxy-5β-pregnan-20-one; 3α,5β-Tetrahydroprogesterone; 3α,5β-THP; 3α-Hydroxy-5β-tetrahydroprogesterone
ECHA InfoCard 100.162.192
C 21 H 34 O 2
g·mol 318.501 −1
0.9–3.5 hours  
Except where otherwise noted, data are given for materials in their
(at 25 °C [77 °F], 100 kPa).
Pregnanolone, also known as eltanolone, is an endogenous inhibitory neurosteroid which is produced in the body from progesterone. It is closely related to  allopregnanolone, which has similar properties.
Pregnanolone is a
positive allosteric modulator of the GABA, A receptor as well as a  negative allosteric modulator of the glycine receptor.
sedative, anxiolytic, anesthetic, and anticonvulsant effects.   During  pregnancy, pregnanolone and allopregnanolone are involved in sedation and anesthesia of the fetus. 
Pregnanolone is synthesized from
progesterone via the enzymes 5β-reductase and 3α-hydroxysteroid dehydrogenase, with 5β-dihydroprogesterone occurring as a metabolic intermediate. The elimination half-life of pregnanolone is between 0.9 and 3.5 hours.  
Pregnanolone, also known as 3α,5β-tetrahydroprogesterone (3α,5β-THP) or as 5β-pregnan-3α-ol-20-one, is a
naturally occurring pregnane steroid and a derivative of progesterone. Related compounds include allopregnanolone (3α,5α-THP; brexanolone), epipregnanolone (3β,5β-THP), hydroxydione, isopregnanolone (3β,5α-THP), and renanolone.
Pregnanolone was first isolated from the
urine of pregnant women in 1937. Its anesthetic properties were first demonstrated in animals in 1957. 
Pregnanolone was investigated for clinical use as a
general anesthetic under the name eltanolone ( ), but produced unwanted INN side effects such as convulsions on occasion, and for this reason, was never marketed.  
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Lagercrantz H, Changeux JP (2009). "The emergence of human consciousness: from fetal to neonatal life". Pediatr. Res. 65 (3): 255–60. doi: 10.1203/PDR.0b013e3181973b0d. PMID 19092726. [...] the fetus is sedated by the low oxygen tension of the fetal blood and the neurosteroid anesthetics pregnanolone and the sleep-inducing prostaglandin D2 provided by the placenta (36).
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