RESEARCH MONOGRAPH · KDC-MN-161

Brexanolone

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

Our opinion on this compound

76/100

Allopregnanolone in an IV bag, FDA-approved, and the proof-of-concept that neurosteroid antidepressants work

Brexanolone is allopregnanolone formulated for IV infusion in a beta-cyclodextrin vehicle. That's it. The molecule itself is endogenous, the trick was finding a way to deliver therapeutic plasma levels for long enough to drive sustained effect, since oral bioavailability is essentially zero.

The phase 2 and phase 3 data in postpartum depression were unusually clean. Sage Therapeutics ran the HUMMINGBIRD trials with HAM-D reductions that beat placebo on day 3 of the 60-hour infusion and held through day 30. For severe PPD specifically, the response rates were the kind of numbers psychiatry rarely sees outside of ECT.

FDA approval came in 2019 with the trade name Zulresso. The catch is that the infusion has to happen in a certified facility under monitoring (REMS program) because the sedative effects at therapeutic doses are non-trivial, which has limited real-world uptake despite the efficacy. Zuranolone (oral analog, FDA approved 2023 as Zurzuvae) was the obvious follow-on to solve the delivery problem, though oral pharmacokinetics produce a different exposure profile and the clinical signal is more modest.

Mechanism-wise see the allopregnanolone entry. Positive allosteric modulation of GABA-A, particularly extrasynaptic delta-subunit receptors mediating tonic inhibition. The durable antidepressant effect after only 60 hours of exposure is the interesting part and probably involves downstream synaptic plasticity, not just receptor occupancy during the infusion window.

Sourcing for research purposes: this is essentially synthetic allopregnanolone formulated with sulfobutylether-beta-cyclodextrin (Captisol) to solubilize the lipophilic steroid for aqueous IV use. The neat compound is well-characterized synthetically. As a finished drug product it's tightly controlled.

What we like: the cleanest validation of the neurosteroid antidepressant hypothesis we have. The proof that postpartum depression has a specific neurosteroid component you can actually target. What we dont like: the delivery problem has limited the clinical impact even though the pharmacology is real. Zuranolone solves that, but at the cost of some of the magnitude.

From a research perspective, this is one of the more important CNS approvals of the past decade and the foundation under a real class of antidepressants.

Evidence: 92
Mechanism: 88
Reliability: 85
Safety: 72
Sourcing: 70
Value: 35
Signal: 80
Staying power: 82

Plain-language summary Intrigue 78 / 100

Brexanolone, sold as Zulresso, is recombinant allopregnanolone administered as a 60-hour IV infusion for postpartum depression. The first FDA-approved postpartum depression specific treatment (2019). 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.

Synthetic allopregnanolone (IV)

Synthetic allopregnanolone formulated for IV administration, FDA-approved as Zulresso for postpartum depression.

Abstract

Brexanolone (Zulresso; SAGE-547; CAS 516-54-1, same as endogenous allopregnanolone) is a synthetic preparation of allopregnanolone formulated for 60-hour intravenous infusion, developed by Sage Therapeutics and approved by the FDA in 2019 for postpartum depression. The compound is identical in structure to endogenous allopregnanolone; the development innovation was the formulation enabling sustained therapeutic plasma concentrations through prolonged IV infusion. Mechanism is GABA-A receptor positive allosteric modulation. Schedule IV. Restricted distribution program (REMS) due to risk of excessive sedation and loss of consciousness. The closely related zuranolone provides oral dosing with similar pharmacology.

Mechanism of action

GABA-A positive allosteric modulator (synthetic allopregnanolone).

Reported research dose ranges

Reported research dose ranges in the literature: 60 to 90 mcg/kg/hr IV reported over a 60-hour infusion.

References

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

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KDC-MN-161

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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Brexanolone

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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