RESEARCH MONOGRAPH · KDC-MN-159

Allopregnanolone

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

78/100

The neurosteroid that actually validated the whole GABA-A neurosteroid hypothesis, and brexanolone proved it

Allopregnanolone is the one that vindicated a whole field. For decades the neurosteroid hypothesis was theoretically cool but clinically unproven, then brexanolone (which is just IV allopregnanolone) got FDA approval for postpartum depression in 2019 with frankly striking response curves in the phase 3 trials. That's the kind of validation most CNS targets never get.

The mechanism is one of the cleanest in neuropharmacology. Allopregnanolone is a positive allosteric modulator at GABA-A receptors with particular activity at delta-subunit-containing extrasynaptic receptors, which mediate tonic inhibition. That tonic inhibition pathway is mechanistically distinct from the phasic inhibition that benzos hit, and that distinction is probably why the antidepressant effects look different from what you get with conventional GABAergic drugs.

Endogenously it fluctuates with the menstrual cycle (peak luteal phase), pregnancy (huge ramp, dramatic postpartum crash, which is the whole brexanolone rationale), and stress. The third-trimester to postpartum drop is something like a 100-fold swing, and you can see why a brain that's been bathed in tonic GABA-A potentiation for nine months responds to that withdrawal.

What's interesting is the time-course. Brexanolone takes 60 hours of IV infusion and produces sustained antidepressant effect lasting 30 days, which is weird for a compound with a short half-life. So whatever the durable effect is, it's downstream plasticity, not just acute receptor occupancy.

Sourcing-wise, allopregnanolone is a synthetic steroid, well-characterized, HPLC straightforward. Research-grade material from reputable suppliers is usually clean. Bioavailability orally is dreadful, which is why brexanolone is IV and zuranolone (the oral analog) was redesigned for that purpose.

What we like: this is one of the most mechanistically interesting GABAergic stories in modern CNS pharmacology, and it actually translated. What we dont like: the marketing-side conflation of allopregnanolone with pregnenolone, which are not the same molecule and not even in the same pharmacological class.

Evidence: 88
Mechanism: 90
Reliability: 82
Safety: 75
Sourcing: 78
Value: 50
Signal: 80
Staying power: 85

Plain-language summary Intrigue 80 / 100

Allopregnanolone is a neurosteroid metabolite of progesterone that powerfully potentiates GABA-A receptors. Recombinant allopregnanolone (brexanolone) is FDA-approved for postpartum depression. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Endogenous GABA-A neurosteroid

An endogenous GABA-A receptor positive allosteric modulator; the active substance in brexanolone for postpartum depression.

Abstract

Allopregnanolone (3α-hydroxy-5α-pregnan-20-one; CAS 516-54-1; molecular formula C21H34O2; molecular weight 318.49) is an endogenous neurosteroid synthesized from progesterone via 5alpha-reductase and 3alpha-hydroxysteroid dehydrogenase. The compound is a potent positive allosteric modulator of GABA-A receptors with anxiolytic, sedative, and anticonvulsant activity. Allopregnanolone declines acutely after parturition, contributing to postpartum depression risk. The compound is the active substance in brexanolone (Zulresso, FDA-approved 2019 for postpartum depression, IV infusion). The closely related zuranolone (Zurzuvae, FDA-approved 2023) is an oral analog with similar pharmacology.

Mechanism of action

Potent GABA-A receptor positive allosteric modulator; binds at distinct site from benzodiazepines.

Reported research dose ranges

Reported research dose ranges in the literature: brexanolone reported in the 60 to 90 mcg/kg/hr IV range; zuranolone reported around 50 mg oral.

References

Meltzer-Brody S, et al. Brexanolone injection in post-partum depression. Lancet 2018.

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KDC-MN-159

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

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Allopregnanolone

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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