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Name: Allopregnanolone
Synonyms: brexanolone, 3α-hydroxy-5α-pregnan-20-one, 3α,5α-tetrahydroprogesterone
Therapy Type: Small Molecule (timeline)
Target Type: Other Neurotransmitters (timeline), Other (timeline)
Condition(s): Alzheimer's Disease
U.S. FDA Status: Alzheimer's Disease (Phase 2)
Status in Select Countries: Approved for postpartum depression


Allopregnanolone is a neurosteroid metabolite of progesterone. It is an allosteric modulator of inhibitory γ-aminobutyric acid (GABA-A) receptors on neural stem cells and other cell types in the brain (Luchetti et al., 2011). Allopregnanolone levels have been reported to be reduced in the temporal cortices of people with Alzheimer's disease (Naylor et al., 2010).

In transgenic Alzheimer's mouse models, allopregnanolone has been reported to increase neurogenesis, reduce amyloid deposition, and improve performance on learning and memory tests (e.g., Wang et al., 2010; Chen et al., 2011; Zhang et al., 2015). The drug also has been proposed to promote neuron and oligodendrocyte maturation and improve mitochondrial function in AD mice (Chen et al., 2020; Wang et al., 2020). In mouse models of the lipid storage disease Niemann-Pick Type C, restoring low allopregnanolone levels lengthened survival, a neuroprotective effect thought to be mediated by the pregnane X steroid receptor (Sep 2006 news).

The rationale behind evaluating allopregnanolone in Alzheimer's is that a combined regenerative and neuroprotective effect may counteract ongoing neuronal cell loss in this neurodegenerative disease (Brinton & Wang, 2006Brinton, 2013Irwin et al., 2014). However, other studies have reported that allopregnanolone can impair learning function in two different AD mouse strains (e.g., Bengtsson et al., 2013). Newer data indicate that continuous elevation of allopregnanolone in mice worsens amyloid load and learning, while intermittent dosing has opposite, beneficial effects (Bengtsson et al., 2020).


From August 2014 to February 2018, an NIH-funded Phase 1 study compared 2, 4, and 6 up to 18 mg of allopregnanolone to placebo, all infused once a week for three months. Conducted at the University of Southern California, the study enrolled 24 men and women with a clinical diagnosis of MCI due to AD or mild AD; 18 received allopregnanolone and 6, placebo. Primary outcome measures include various safety parameters including brain MRI; secondary outcomes are pharmacokinetics, cognitive batteries, and structural and functional MRI. Both drug and placebo were being manufactured at the University of California, Davis (see Dec 2014 conference newsAug 2013 conference news).

According to trial results presented at the 2018 CTAD meeting, the 2, 4, and 6 mg doses produced no adverse events or amyloid-related imaging abnormalities on MRI, and clinical results remained in the normal range. The drug caused sleepiness at 10 mg in women and 6 mg in men. Treatment was associated with less atrophy of the left hippocampus compared to placebo, more so in APOE4 carriers. The 4 and 6 mg doses improved functional connectivity in some brain regions. Exploratory cognitive measures found high variability and no significant differences between drug and placebo groups (Nov 2018 conference news). Results were published (Hernandez et al., 2020). Additional analysis of exploratory imaging data indicated that allo treatment improved white matter integrity and functional connectivity in some brain regions (Raikes et al., 2022).

In October 2019, a Phase 1 dose-finding study at the University of Southern California began testing intramuscular injections of allopregnanolone in lieu of infusions. The trial is enrolling 12 people with MCI due to AD or mild AD to receive 4 to 18 mg of drug weekly for up to four weeks, with pharmacokinetic analysis to determine the equivalent dose to the 4 mg infusion. Participants will continue that dose for a total of 12 weeks. Endpoints are safety, pharmacokinetics, patient satisfaction, and feasibility. Other outcomes include MRI measures of brain volume, standard tests of cognition, daily function, sleep quality, and physical activity. The trial is slated to finish in October 2022.

A 200-participant Phase 2 trial was scheduled to start in November 2021. Participants will have probable AD and carry an ApoE4 allele, but the trial requires no biomarker confirmation of Alzheimer's as underlying etiology. Participants will be randomized to 4 mg allopregnanolone or placebo infusion once weekly for 12 months, followed by a 6-month, open-label extension. The primary outcome is hippocampal volume. Secondary outcomes include measures of cognition and function, safety, and tolerability. Blood markers, various MRI modalities, as well as clinical measures will serve as exploratory outcomes.

Allopregnanolone is also being evaluated in traumatic brain injury, as well as post-traumatic stress, depression, and anxiety disorders.

For all trials of allopregnanolone, see

Last Updated: 05 Apr 2022


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News Citations

  1. Just for Her? Study of Women’s Biology Offers New Therapeutic Angle
  2. Clinical Trials Roundup: Broadening the Lines of Attack
  3. Fits and Starts: Trial Results from the CTAD Conference
  4. Cholesterol Metabolites Protect Neurons in Niemann-Pick C Disease

Paper Citations

  1. . Safety, tolerability, and pharmacokinetics of allopregnanolone as a regenerative therapeutic for Alzheimer's disease: A single and multiple ascending dose phase 1b/2a clinical trial. Alzheimers Dement (N Y). 2020;6(1):e12107. Epub 2020 Dec 16 PubMed.
  2. . Neurosteroid and GABA-A receptor alterations in Alzheimer's disease, Parkinson's disease and multiple sclerosis. Neuroscience. 2011 Sep 15;191:6-21. PubMed.
  3. . Allopregnanolone levels are reduced in temporal cortex in patients with Alzheimer's disease compared to cognitively intact control subjects. Biochim Biophys Acta. 2010 Aug;1801(8):951-9. PubMed.
  4. . Allopregnanolone reverses neurogenic and cognitive deficits in mouse model of Alzheimer's disease. Proc Natl Acad Sci U S A. 2010 Apr 6;107(14):6498-503. Epub 2010 Mar 15 PubMed.
  5. . Allopregnanolone promotes regeneration and reduces β-amyloid burden in a preclinical model of Alzheimer's disease. PLoS One. 2011;6(8):e24293. PubMed.
  6. . Allopregnanolone enhances the neurogenesis of midbrain dopaminergic neurons in APPswe/PSEN1 mice. Neuroscience. 2015 Apr 2;290:214-26. Epub 2015 Jan 28 PubMed.
  7. . Allopregnanolone Promotes Neuronal and Oligodendrocyte Differentiation In Vitro and In Vivo: Therapeutic Implication for Alzheimer's Disease. Neurotherapeutics. 2020 Jul 6; PubMed.
  8. . Allopregnanolone Reverses Bioenergetic Deficits in Female Triple Transgenic Alzheimer's Mouse Model. Neurotherapeutics. 2020 Jan;17(1):178-188. PubMed.
  9. . Neurosteroids as regenerative agents in the brain: therapeutic implications. Nat Rev Endocrinol. 2013 Feb 26; PubMed.
  10. . Frontiers in therapeutic development of allopregnanolone for Alzheimer's disease and other neurological disorders. Front Cell Neurosci. 2014;8:203. Epub 2014 Jul 30 PubMed.
  11. . Brief but Chronic Increase in Allopregnanolone Cause Accelerated AD Pathology Differently in Two Mouse Models. Curr Alzheimer Res. 2013 Jan 1;10(1):38-47. PubMed.
  12. . GABA-A receptor modulating steroids in acute and chronic stress; relevance for cognition and dementia?. Neurobiol Stress. 2020 May;12:100206. Epub 2019 Dec 20 PubMed.

External Citations

  1. Raikes et al., 2022
  3. Brinton & Wang, 2006

Further Reading


  1. . Allopregnanolone and neurogenesis in the nigrostriatal tract. Front Cell Neurosci. 2014;8:224. Epub 2014 Aug 12 PubMed.
  2. . Revisiting the roles of progesterone and allopregnanolone in the nervous system: resurgence of the progesterone receptors. Prog Neurobiol. 2014 Feb;113:6-39. Epub 2013 Oct 27 PubMed.
  3. . Allopregnanolone as regenerative therapeutic for Alzheimer's disease: Translational development and clinical promise. Prog Neurobiol. 2013 Sep 14; PubMed.
  4. . Allopregnanolone Increases the Number of Dopaminergic Neurons in Substantia Nigra of Triple Transgenic Mouse Model of Alzheimer's Disease. Curr Alzheimer Res. 2012 Jan 23; PubMed.
  5. . Allopregnanolone restores hippocampal-dependent learning and memory and neural progenitor survival in aging 3xTgAD and nonTg mice. Neurobiol Aging. 2011 Jul 29; PubMed.
  6. . Neurosteroid biosynthetic pathways changes in prefrontal cortex in Alzheimer's disease. Neurobiol Aging. 2011 Nov;32(11):1964-76. PubMed.
  7. . Alternatives to amyloid for Alzheimer's disease therapies-a symposium report. Ann N Y Acad Sci. 2020 Sep;1475(1):3-14. Epub 2020 May 29 PubMed.
  8. . Microglial Cell Morphology and Phagocytic Activity Are Critically Regulated by the Neurosteroid Allopregnanolone: A Possible Role in Neuroprotection. Cells. 2021 Mar 21;10(3) PubMed.
  9. . Neurosteroid allopregnanolone (3α,5α-THP) inhibits inflammatory signals induced by activated MyD88-dependent toll-like receptors. Transl Psychiatry. 2021 Feb 26;11(1):145. PubMed.