Neurosteroid antidepressants explained

What neurosteroid antidepressants are

Neurosteroids are a class of steroid molecules made in the brain that modulate neuronal signaling. Allopregnanolone is one of the best-characterized neurosteroids. It's a metabolite of progesterone and acts as a positive allosteric modulator of the GABA-A receptor, which is the main inhibitory receptor in the brain. Allopregnanolone levels rise sharply during pregnancy and fall equally sharply after delivery. That postpartum drop is thought to contribute to postpartum depression in vulnerable women.

Brexanolone (Zulresso) is a proprietary formulation of allopregnanolone itself, delivered as a 60-hour continuous IV infusion. It was FDA-approved in 2019 for postpartum depression.

Zuranolone (Zurzuvae) is an oral analog of allopregnanolone, given once nightly for 14 days. It was FDA-approved in 2023 for postpartum depression. The FDA declined to approve zuranolone for major depressive disorder in the general population, citing efficacy questions. Its indication is postpartum depression specifically.

Both medications differ from most other antidepressants in two ways worth naming. First, they work fast, with mood improvement within days rather than weeks. Second, they're given as a defined time-limited course rather than as ongoing daily treatment. That's an unusual model for antidepressant care.

The medications covered here are brexanolone (Zulresso) and zuranolone (Zurzuvae).

How they work

GABA (gamma-aminobutyric acid) is the main inhibitory chemical messenger in the brain. When GABA binds to its receptor (GABA-A), the receptor lets chloride ions into the neuron, which makes the neuron less likely to fire. GABA-A receptors are complex proteins made of five subunits, and they have several binding sites where other molecules can influence their activity.

Benzodiazepines act at one binding site on GABA-A receptors, on receptors that contain specific subunit types. Their action is called positive allosteric modulation, meaning they don't activate the receptor themselves but make GABA's own action stronger when GABA is present.

Allopregnanolone acts at a different binding site on GABA-A receptors. Importantly, it acts on both synaptic GABA-A receptors (the ones that mediate quick, phasic inhibition) and extrasynaptic GABA-A receptors that contain the delta subunit (which mediate slow, tonic inhibition). Extrasynaptic GABA-A receptors sit outside the direct synapse and respond to ambient GABA levels. They're thought to be particularly important in setting the overall excitability of certain brain circuits. This action on extrasynaptic receptors is one thing that makes neurosteroids different from benzodiazepines and may explain their antidepressant effect.

Brexanolone and zuranolone both act at these sites. Zuranolone's molecular design was aimed at achieving oral bioavailability with useful duration, which allopregnanolone itself (and brexanolone by extension) lacks. Zuranolone is dosed once daily at bedtime because peak sedation happens shortly after dosing.

The theory for postpartum depression is that plummeting allopregnanolone levels after delivery destabilize GABA-A signaling in vulnerable women. Restoring that signaling for a defined period allows recovery. Whether the same mechanism explains benefit in non-postpartum depression is less clear, and it's part of why zuranolone's non-postpartum MDD application wasn't approved.

How the class developed

The story goes back to research on allopregnanolone in the 1980s and 1990s, when its interactions with GABA-A receptors were worked out. A biotech company called Sage Therapeutics developed brexanolone as a stabilized formulation of allopregnanolone that could be given IV. Trials in postpartum depression showed rapid improvement in depression scores within 60 hours, and brexanolone was approved by the FDA in 2019 as the first medication specifically approved for postpartum depression.

The practical limits of brexanolone became clear quickly. A 60-hour IV infusion requires an inpatient or infusion-center setting, continuous monitoring, and is expensive. Uptake was limited by the logistics, not by whether it worked.

Zuranolone was developed to solve that logistics problem. As an oral analog, it can be taken at home, and the 14-day course fits into a mother's life in a way a 60-hour infusion doesn't. It received FDA approval for postpartum depression in August 2023.

The neurosteroid class is early in its story. Whether other neurosteroid analogs, other indications (bipolar, catamenial epilepsy, tremor), or improved formulations will follow is being studied.

What they treat

Postpartum depression. Both brexanolone and zuranolone are FDA-approved specifically for postpartum depression. In practice this means a mother experiencing a depressive episode within the postpartum period, generally within about a year of delivery.

Neither is currently approved for major depressive disorder outside the postpartum context. Zuranolone was submitted for that broader indication and the FDA didn't approve it, citing efficacy that wasn't as strong as required for approval in non-postpartum MDD.

Both work fast. That matters in postpartum depression, where the effect on the mother, the infant, and the mother-infant bond can be substantial and where a four-to-six-week wait for a standard antidepressant to work is a long time.

Individual medications in this class

• Brexanolone (Zulresso). Allopregnanolone infusion. Given as a 60-hour continuous IV infusion at a certified healthcare facility. FDA-approved for postpartum depression. Requires the REMS program with continuous pulse oximetry and observation for sedation and syncope. Uptake has been limited by logistics and cost.
• Zuranolone (Zurzuvae). Oral neurosteroid GABA-A positive allosteric modulator. 50 mg once daily at bedtime for 14 days is the standard course. FDA-approved for postpartum depression. Doesn't require a REMS program in the same form as brexanolone, but carries a boxed warning about driving impairment and can't be taken with driving the following day.

Common side effects across the class

Sedation and sleepiness. This is the most consistent effect and is expected. Zuranolone is dosed at bedtime for this reason. Brexanolone is given inpatient with monitoring specifically because sedation can be significant.

Dizziness.

Headache.

Diarrhea.

Fatigue.

Dry mouth.

Zuranolone specific: sedation, dizziness, drowsiness, common cold symptoms, upper respiratory infection, and diarrhea were the most common in trials. Some people notice an activating effect the day after dosing that improves as the course progresses.

Brexanolone specific: sedation, dry mouth, loss of consciousness or excessive sedation (which is the reason for the continuous monitoring), and flushing were common in trials.

Both medications, being GABA-A positive modulators, can produce feelings of sedation, unsteadiness, or slowed thinking that resemble other GABAergic medications. Alcohol should be avoided during treatment.

Serious warnings across the class

Brexanolone boxed warning. Loss of consciousness and excessive sedation during infusion. Continuous pulse oximetry is required, and the patient must be attended by a caregiver during dosing. Any infant present must have another caregiver available. Falls and syncope have been reported.

Brexanolone REMS. Only administered in certified facilities. Continuous monitoring for pulse oximetry through the 60-hour infusion. Patient must remain on-site for the entire infusion. Any planned care of an infant during the infusion requires a caregiver other than the patient.

Zuranolone boxed warning. Driving impairment. Zuranolone can cause significant next-morning impairment even in people who don't feel sleepy. Patients cannot drive or engage in activities requiring full alertness for at least 12 hours after taking the dose. That's not a suggestion. It's the reason zuranolone is dosed at bedtime.

Suicidal thoughts. As with other antidepressants, the antidepressant boxed warning about possible increases in suicidal thoughts in people under 25 applies.

CNS depression with other agents. Combining brexanolone or zuranolone with opioids, benzodiazepines, alcohol, or other CNS depressants raises sedation and respiratory depression risk. This is worth clarifying in the postpartum period, when patients may also be on pain medications or benzodiazepines for anxiety.

Fetal exposure and lactation. Both medications transfer to some degree into breast milk. Brexanolone labeling addresses this and provides guidance. Zuranolone labeling addresses this too. Whether to hold breastfeeding, hold the medication, or continue both is a discussion to have with the prescriber. Untreated postpartum depression has its own risks to the infant, so weighing those trade-offs is part of the decision.

Interactions. Zuranolone is a CYP3A4 substrate. Strong CYP3A4 inhibitors and inducers can affect drug levels, and dose adjustments may be needed.

What tips the choice within the class

Brexanolone versus zuranolone. In practice, most postpartum depression treated with a neurosteroid now uses zuranolone. The 14-day oral course fits into life in a way a 60-hour hospital infusion doesn't, and access to brexanolone remains limited by REMS-required certified facilities. Brexanolone is still an option when someone has particularly severe postpartum depression, needs immediate inpatient care, and is a candidate for the monitored setting.

Timing. Both work fast. If the goal is rapid improvement of severe postpartum depression, a neurosteroid is a strong option. If the depression is mild to moderate, SSRIs remain the standard, and the choice between a neurosteroid and an SSRI factors in cost, speed, breastfeeding considerations, and access.

Breastfeeding. Both medications transfer into breast milk. SSRIs have decades of postpartum data and generally low breastfeeding concern (sertraline is often first-line). Neurosteroids have less breastfeeding data. Some prescribers and patients choose to pump and dump during a zuranolone course, or briefly hold breastfeeding, and resume after the course ends. Others use zuranolone while continuing breastfeeding after weighing the specific data. This is a discussion for the prescriber and, ideally, a lactation-informed clinician.

Non-postpartum depression. Neither medication is currently indicated for MDD outside the postpartum context. Standard antidepressants (SSRIs, SNRIs, atypicals) remain the answer for non-postpartum depression.

Cost and access. Brexanolone requires a certified inpatient or infusion setting and has been very expensive. Zuranolone is oral and dispensed through specialty pharmacies. Insurance coverage varies.

Follow-up. Zuranolone is a 14-day course. After the course, ongoing care planning matters. Some patients need additional treatment for depression that returns after the course. Some are stable and don't need further medication. That planning starts before the course ends.

Common questions

How is zuranolone different from an SSRI? Several ways. First, mechanism. Zuranolone acts on GABA-A receptors, a different system than SSRIs, which act on serotonin. Second, timeline. Zuranolone can produce mood improvement within days, where SSRIs take four to six weeks. Third, duration of treatment. Zuranolone is a 14-day course rather than ongoing daily use. Fourth, indication. Zuranolone is approved specifically for postpartum depression. SSRIs are approved for major depressive disorder and several anxiety conditions. Zuranolone isn't intended to replace SSRIs for depression outside the postpartum period.

Why is brexanolone given as a 60-hour infusion? Because allopregnanolone itself doesn't work well as a pill (poor oral bioavailability) and because a steady blood level over about 60 hours was what produced the antidepressant effect in trials. The infusion is titrated up over several hours, held at maintenance level for a period, and then tapered down. The continuous exposure over 60 hours is what does the work. Zuranolone was developed specifically to get around this logistics problem by being taken orally.

Can I drive during a course of zuranolone? Not for at least 12 hours after each dose. The boxed warning is specifically about driving impairment. Even people who don't feel sleepy the morning after can have measurable impairment. That's why zuranolone is taken at bedtime and why patients are told not to drive the following morning until at least 12 hours have passed. During the 14-day course, this means planning around it: a partner or family member drives the kids to school, or arrangements are made for essential errands. It's a real logistics consideration.

Can I breastfeed while taking zuranolone or brexanolone? Both medications transfer into breast milk. The amount and clinical impact aren't as well characterized as for SSRIs, which have decades of postpartum data. Some clinicians recommend continuing breastfeeding while monitoring the infant for sedation and feeding changes. Others recommend pumping and discarding milk during treatment (and for a period after) and using formula. This depends on the specific medication, the depth of postpartum depression, and the mother-infant preferences. It's a discussion to have with the prescriber and, ideally, a lactation-informed clinician. Untreated postpartum depression has its own risks to the infant, which is part of the balance.

Does zuranolone work for depression outside the postpartum period? Zuranolone was submitted for FDA approval for major depressive disorder in general and wasn't approved. The FDA cited efficacy that wasn't strong enough for approval in non-postpartum MDD. Zuranolone is FDA-approved specifically for postpartum depression. Whether some clinicians will use it off-label for other depressive conditions remains to be seen, but the approved use, and the setting where the evidence is strongest, is postpartum depression.

Sources

This guide draws on current prescribing information and public health references. It's reviewed for clinical accuracy and updated as guidance changes. This is educational content and isn't medical advice.

1. U.S. Food and Drug Administration. Prescribing information for Zulresso and Zurzuvae.
2. MedlinePlus, U.S. National Library of Medicine.
3. National Institute of Mental Health. Perinatal depression.
4. American College of Obstetricians and Gynecologists. Guidance on treatment of perinatal mental health conditions.
5. Deligiannidis KM, et al. Effect of zuranolone vs placebo in postpartum depression. JAMA Psychiatry 2021.
6. Meltzer-Brody S, et al. Brexanolone injection in postpartum depression: two multicentre, double-blind, randomized, placebo-controlled trials. Lancet 2018.