CAS number  N
ChemSpider  YesY
Jmol-3D images Image 1
Molecular formula C21H34O2
Molar mass 318.49 g/mol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N   YesY/N?)

Allopregnanolone (3α-hydroxy-5α-pregnan-20-one or 3α,5α-tetrahydroprogesterone), generally abbreviated as ALLO or as 3α,5α-THP, is an endogenous inhibitory pregnane neurosteroid.[1] It is synthesized from progesterone, and is a potent positive allosteric modulator of the GABAA receptor.[1] Allopregnanolone has effects similar to those of other potentiators of the GABAA receptor such as the benzodiazepines, including anxiolytic, sedative, and anticonvulsant activity.[1]

The 21-hydroxylated derivative of this compound, tetrahydrodeoxycorticosterone (THDOC), is an endogenous inhibitory neurosteroid with similar properties to those of allopregnanolone, and the 3β-methyl analogue of allopregnanolone, ganaxolone, is under development to treat epilepsy and other conditions.[1]


  • Biosynthesis 1
  • Mechanism 2
  • Function 3
  • Therapeutic applications 4
  • See also 5
  • References 6
  • Additional reading 7


The biosynthesis of allopregnanolone starts with the conversion of progesterone into 5α-dihydroprogesterone by 5α-reductase type I. After that, 3α-hydroxysteroid dehydrogenase converts this intermediate into allopregnanolone.[1]

Depression, anxiety, and sexual dysfunction are frequently-seen side effects of 5α-reductase inhibitors such as finasteride, and are thought to be caused, in part, by interfering with the normal production of allopregnanolone.[2]


Allopregnanolone acts as a potent positive allosteric modulator of the GABAA receptor.[1] While allopregnanolone, like other inhibitory neurosteroids such as THDOC, positively modulates all GABAA receptor isoforms, those isoforms containing δ subunits exhibit the greatest potentiation.[1] Allopregnanolone has also been found to act as a positive allosteric modulator of the GABAA-ρ receptor, though the implications of this action are unclear.[3][4] In addition to its actions on GABA receptors, allopregnanolone, like progesterone, is known to be a negative allosteric modulator of nACh receptors,[5] and also appears to act as a negative allosteric modulator of the 5-HT3 receptor.[6] Along with the other inhibitory neurosteroids, allopregnanolone appears to have little or no action at other ligand-gated ion channels, including the NMDA, AMPA, kainate, and glycine receptors.[7]

Unlike progesterone, allopregnanolone is inactive at the nuclear progesterone receptor (nPR).[7] However, allopregnanolone can be intracellularly oxidized into 5α-dihydroprogesterone, which is an agonist of the nPR, and thus/in accordance, allopregnanolone does appear to have indirect nPR-mediated progestogenic effects.[8] In addition, allopregnanolone has recently been found to be an agonist of the newly discovered membrane progesterone receptors (mPR), including mPRδ, mPRα, and mPRβ, with its activity at these receptors about a magnitude more potent than at the GABAA receptor.[9][10] The action of allopregnanolone at these receptors may be related, in part, to its neuroprotective and antigonadotropic properties.[9][11] Also like progesterone, recent evidence has shown that allopregnanolone is an activator of the pregnane X receptor.[7][12]

Similarly to many other GABAA receptor positive allosteric modulators, allopregnanolone has been found to act as an inhibitor of L-type voltage-gated calcium channels (L-VGCCs),[13] including α1 subtypes Cav1.2 and Cav1.3.[14] However, the threshold concentration of allopregnanolone to inhibit L-VGCCs was determined to be 3 μM (3,000 nM), which is far greater than the concentration of 5 nM that has been estimated to be naturally produced in the human brain.[14] Thus, inhibition of L-VGCCs is unlikely of any actual significance in the effects of endogenous allopregnanolone.[14] Also, allopregnanolone, along with several other neurosteroids, has been found to activate the G protein-coupled bile acid receptor (GPBAR1, or TGR5).[15] However, it is only able to do so at micromolar concentrations, which, similarly to the case of the L-VGCCs, are far greater than the low nanomolar concentrations of allopregnanolone estimated to be present in the brain.[15]


Allopregnanolone possesses a wide variety of effects, including, in no particular order, antidepressant, anxiolytic, stress-reducing, rewarding,[16] prosocial,[17] antiaggressive,[18] prosexual,[17] sedative, pro-sleep,[19] cognitive and memory-impairing, analgesic,[20] anesthetic, anticonvulsant, neuroprotective, and neurogenic effects.[1]

Fluctuations in the levels of allopregnanolone and the other neurosteroids seem to play an important role in the pathophysiology of mood, anxiety, premenstrual syndrome, catamenial epilepsy, and various other neuropsychiatric conditions.[21][22][23]

Increased levels of allopregnanolone can produce paradoxical effects, including negative mood, anxiety, irritability, and aggression.[24][25][26] This appears to be because allopregnanolone possesses biphasic, U-shaped actions at the GABAA receptor – moderate level increases (in the range of 1.5–2 nM/L total allopregnanolone, which are approximately equivalent to luteal phase levels) inhibit the activity of the receptor, while lower and higher concentration increases stimulate it.[24][25] This seems to be a common effect of many GABAA receptor positive allosteric modulators.[26][21] In accordance, acute administration of low doses of micronized progesterone (which reliably elevates allopregnanolone levels), have been found to have negative effects on mood, while higher doses have a neutral effect.[27]

Therapeutic applications

Allopregnanolone and the other endogenous inhibitory neurosteroids have very short half-lives, and for this reason, have not been pursued for clinical use themselves. Instead, synthetic analogs with improved pharmacokinetic profiles, such as ganaxolone, have been synthesized and are being investigated. However, exogenous progesterone, such as oral micronized progesterone (OMP), reliably elevates allopregnanolone levels in the body with good dose-to-serum level correlations.[28] Due to this, it has been suggested that OMP could be described as a prodrug of sorts for allopregnanolone.[28] As a result, there has been some interest in using OMP to treat catamenial epilepsy,[29] as well as other menstrual cycle-related and neurosteroid-associated conditions.

See also


  1. ^ a b c d e f g h Reddy DS (2010). "Neurosteroids: endogenous role in the human brain and therapeutic potentials". Prog. Brain Res. 186: 113–37.  
  2. ^ Römer B, Gass P (December 2010). "Finasteride-induced depression: new insights into possible pathomechanisms". J Cosmet Dermatol 9 (4): 331–2.  
  3. ^ Morris KD, Moorefield CN, Amin J (October 1999). "Differential modulation of the gamma-aminobutyric acid type C receptor by neuroactive steroids". Mol. Pharmacol. 56 (4): 752–9.  
  4. ^ Li W, Jin X, Covey DF, Steinbach JH (October 2007). "Neuroactive steroids and human recombinant rho1 GABAC receptors". J. Pharmacol. Exp. Ther. 323 (1): 236–47.  
  5. ^ Bullock AE, Clark AL, Grady SR, et al. (June 1997). "Neurosteroids modulate nicotinic receptor function in mouse striatal and thalamic synaptosomes". J. Neurochem. 68 (6): 2412–23.  
  6. ^ Wetzel CH, Hermann B, Behl C, et al. (September 1998). "Functional antagonism of gonadal steroids at the 5-hydroxytryptamine type 3 receptor". Mol. Endocrinol. 12 (9): 1441–51.  
  7. ^ a b c Mellon SH (October 2007). "Neurosteroid regulation of central nervous system development". Pharmacol. Ther. 116 (1): 107–24.  
  8. ^ Rupprecht R, Reul JM, Trapp T, et al. (September 1993). "Progesterone receptor-mediated effects of neuroactive steroids". Neuron 11 (3): 523–30.  
  9. ^ a b Thomas P, Pang Y (2012). "Membrane progesterone receptors: evidence for neuroprotective, neurosteroid signaling and neuroendocrine functions in neuronal cells". Neuroendocrinology 96 (2): 162–71.  
  10. ^ Pang Y, Dong J, Thomas P (January 2013). "Characterization, neurosteroid binding and brain distribution of human membrane progesterone receptors δ and {epsilon} (mPRδ and mPR{epsilon}) and mPRδ involvement in neurosteroid inhibition of apoptosis". Endocrinology 154 (1): 283–95.  
  11. ^ Sleiter N, Pang Y, Park C, et al. (August 2009). "Progesterone receptor A (PRA) and PRB-independent effects of progesterone on gonadotropin-releasing hormone release". Endocrinology 150 (8): 3833–44.  
  12. ^ Lamba V, Yasuda K, Lamba JK, et al. (September 2004). "PXR (NR1I2): splice variants in human tissues, including brain, and identification of neurosteroids and nicotine as PXR activators". Toxicol. Appl. Pharmacol. 199 (3): 251–65.  
  13. ^ Hu AQ, Wang ZM, Lan DM, et al. (July 2007). "Inhibition of evoked glutamate release by neurosteroid allopregnanolone via inhibition of L-type calcium channels in rat medial prefrontal cortex". Neuropsychopharmacology 32 (7): 1477–89.  
  14. ^ a b c Earl DE, Tietz EI (April 2011). "Inhibition of recombinant L-type voltage-gated calcium channels by positive allosteric modulators of GABAA receptors". J. Pharmacol. Exp. Ther. 337 (1): 301–11.  
  15. ^ a b Keitel V, Görg B, Bidmon HJ, et al. (November 2010). "The bile acid receptor TGR5 (Gpbar-1) acts as a neurosteroid receptor in brain". Glia 58 (15): 1794–805.  
  16. ^ Rougé-Pont F, Mayo W, Marinelli M, Gingras M, Le Moal M, Piazza PV (July 2002). "The neurosteroid allopregnanolone increases dopamine release and dopaminergic response to morphine in the rat nucleus accumbens". Eur. J. Neurosci. 16 (1): 169–73.  
  17. ^ a b Frye CA (December 2009). "Neurosteroids' effects and mechanisms for social, cognitive, emotional, and physical functions". Psychoneuroendocrinology. 34 Suppl 1: S143–61.  
  18. ^ Pinna G, Costa E, Guidotti A (February 2005). "Changes in brain testosterone and allopregnanolone biosynthesis elicit aggressive behavior". Proc. Natl. Acad. Sci. U.S.A. 102 (6): 2135–40.  
  19. ^ Terán-Pérez G, Arana-Lechuga Y, Esqueda-León E, Santana-Miranda R, Rojas-Zamorano JÁ, Velázquez Moctezuma J (October 2012). "Steroid hormones and sleep regulation". Mini Rev Med Chem 12 (11): 1040–8.  
  20. ^ Patte-Mensah C, Meyer L, Taleb O, Mensah-Nyagan AG (February 2014). "Potential role of allopregnanolone for a safe and effective therapy of neuropathic pain". Prog. Neurobiol. 113: 70–8.  
  21. ^ a b Bäckström T, Andersson A, Andreé L, et al. (December 2003). "Pathogenesis in menstrual cycle-linked CNS disorders". Ann. N. Y. Acad. Sci. 1007: 42–53.  
  22. ^ Guille C, Spencer S, Cavus I, Epperson CN (July 2008). "The role of sex steroids in catamenial epilepsy and premenstrual dysphoric disorder: implications for diagnosis and treatment". Epilepsy Behav 13 (1): 12–24.  
  23. ^ Finocchi C, Ferrari M (May 2011). "Female reproductive steroids and neuronal excitability". Neurol. Sci. 32 Suppl 1: S31–5.  
  24. ^ a b Bäckström T, Haage D, Löfgren M, et al. (September 2011). "Paradoxical effects of GABA-A modulators may explain sex steroid induced negative mood symptoms in some persons". Neuroscience 191: 46–54.  
  25. ^ a b Andréen L, Nyberg S, Turkmen S, van Wingen G, Fernández G, Bäckström T (September 2009). "Sex steroid induced negative mood may be explained by the paradoxical effect mediated by GABAA modulators". Psychoneuroendocrinology 34 (8): 1121–32.  
  26. ^ a b Bäckström T, Bixo M, Johansson M, et al. (February 2014). "Allopregnanolone and mood disorders". Prog. Neurobiol. 113: 88–94.  
  27. ^ Andréen L, Sundström-Poromaa I, Bixo M, Nyberg S, Bäckström T (August 2006). "Allopregnanolone concentration and mood--a bimodal association in postmenopausal women treated with oral progesterone". Psychopharmacology (Berl.) 187 (2): 209–21.  
  28. ^ a b Andréen L, Spigset O, Andersson A, Nyberg S, Bäckström T (June 2006). "Pharmacokinetics of progesterone and its metabolites allopregnanolone and pregnanolone after oral administration of low-dose progesterone". Maturitas 54 (3): 238–44.  
  29. ^ Orrin Devinsky; Steven Schachter; Steven Pacia (1 January 2005). Complementary and Alternative Therapies for Epilepsy. Demos Medical Publishing. pp. 378–.  

Additional reading

  • Herd, MB; Belelli, D; Lambert, JJ (2007). Neurosteroid modulation of synaptic and extrasynaptic GABA(A) receptors. Pharmacol. Ther. 116(1):20-34.