March 16, 2020
I’m the first drug for treating postpartum depression.
What molecule am I?
Image of Allopregnanolone 3D Image of Allopregnanolone

Allopregnanolone, also commonly called brexanolone, is a metabolite of the sex hormone progesterone that is produced in the brains of mammals. It was first isolated from the urine of pregnant women in 1937 by Russell E. Marker, Oliver Kamm, and Ralph V. McGrew at Penn State (State College, PA) and Parke-Davis (Detroit). The following year, G. Fleischer, B. Whitman, and E. Schwenk at Schering (Bloomfield, NJ) synthesized it from the hormone pregnenolone.

Allopregnanolone modulates the γ-aminobutyric acid (GABA) receptor GABAA in the brain. In 2019, the US Food and Drug Administration approved allopregnanolone as an intravenous infusion for treating postpartum depression (PPD; see the sidebar), the first drug to be approved for this condition. Sage Therapeutics (Cambridge, MA) markets it under the trade name Zulresso.

The 60-h Zulresso infusion reduces the symptoms of PPD almost immediately. Because the patient must be closely monitored, the drug must be administered in a medical facility.

Postpartum depression

Childbirth causes hormonal fluctuations that interact with the host of emotions that accompany the birth of a baby: excitement, joy, fear, anxiety, and even depression. The fear, anxiety, and depression are often described as the baby blues and last from a few days to a couple of weeks.

A more serious complication of birth can be a debilitating depression—postpartum depression, or PPD—which can last for weeks or months. Because most antidepressants can take a few weeks to become effective, the development of a faster-acting medication that specifically targets the hormonal aspects of PPD is significant. 

Allopregnanolone hazard information

Hazard class*Hazard statement
Not a hazardous substance or mixture   

*Globally Harmonized System of Classification and Labeling of Chemicals.

Allopregnanolone fast facts

CAS Reg. No.516-54-1
Pregnan-20-one, 3-hydroxy-, (3α,5α)-
Empirical formulaC21H34O2
Molar mass318.49 g/mol
AppearanceWhite crystalline solid
Melting point177 ºC
Water solubilityVery slight
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Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.

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