A cortisol-targeting antidepressant produced statistically significant improvements in depression that peaked four weeks after patients stopped taking it — and those results have now cleared peer review in the British Journal of Psychiatry, formally elevating the findings from a sponsor announcement to independently scrutinized science.
That unusual durability — remission rates of 26% in treated patients versus 17% in the placebo group, measured at Week 10 after a six-week treatment course — is not just a clinical curiosity. It is what the drug’s mechanism predicts. Xanamem (emestedastat), developed by Australian biotech Actinogen Medical (ASX: ACW), does not work on serotonin or dopamine. It blocks the production of cortisol inside brain cells — and cortisol biology operates on a timeframe of weeks, not hours.
The remission advantage amounts to a 50% higher remission rate for patients on Xanamem compared with those on placebo, measured four weeks after dosing ended.
What Is Xanamem and Why Target Cortisol?
Major depressive disorder affects hundreds of millions of people worldwide, and roughly 30% of them do not adequately respond to at least two rounds of conventional antidepressants — a condition called treatment-resistant depression (TRD).
The existing pharmacological toolkit for TRD includes augmentation with atypical antipsychotics, esketamine nasal spray (Spravato, FDA-approved 2019), and psychedelic-adjacent compounds in late-stage trials from companies such as Compass Pathways. Nearly all of these agents target the same basic neurochemical systems as conventional antidepressants: serotonin, dopamine, and glutamate.
Xanamem takes a different path. The drug selectively inhibits an enzyme called 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), which converts inactive cortisone to active cortisol inside cells. The brain — specifically the hippocampus and frontal cortex — contains high concentrations of this enzyme. By blocking it locally, Xanamem reduces intraneuronal cortisol without touching the adrenal glands, which produce the body’s systemic cortisol.
That distinction is clinically critical. Systemic cortisol regulates immune function, blood pressure, and metabolism. Suppressing it entirely would cause serious harm. Xanamem’s design is intended to lower the brain’s cortisol environment while leaving the body’s stress response intact — a localized intervention at the intracellular level.
The World Health Organization formally recognized this new drug class in early 2025, assigning emestedastat the suffix "-stedastat," designating a previously unnamed category of 11β-HSD1 enzyme inhibitors.
What the XanaCIDD Trial Found: Results and Limits
The XanaCIDD trial was a Phase 2a, randomized, double-blind, placebo-controlled study conducted in 165 participants with moderate major depressive disorder and measurable cognitive impairment. Approximately 80% were receiving background antidepressant therapy (typically an SSRI or SNRI), and the mean number of prior depressive episodes per participant was ten — a population that has not responded to repeated treatment attempts.
Participants received either 10 mg of Xanamem once daily or placebo for six weeks, followed by four weeks of blinded observation with no active drug. The primary endpoint was a composite of cognitive attention and working memory tests.
Xanamem did not meet that primary cognitive endpoint. The placebo group showed unexpectedly large cognitive gains, which compressed the margin needed to detect a drug effect. This is a known challenge in clinical trials of cognitive-enhancing drugs: the test environment itself can produce performance improvements in subjects who are paying close attention and motivated to do well.
The depression story was different. Measured by the Montgomery-Åsberg Depression Rating Scale (MADRS), Xanamem showed statistically significant superiority over placebo, with an effect that grew after treatment stopped. The overall population showed a 2.7-point MADRS advantage at Week 10 (p < 0.05); among the 46% of participants receiving background SSRI therapy, the advantage was 4.2 MADRS points at Week 10 (p < 0.05).
The positive effect extended across five of six pre-specified patient subgroups, and was corroborated by a patient-reported outcome measure, the Patient Global Impression of Severity.
Depression Improved, Cognition Didn’t: What That Dissociation Means
One of the BJP paper’s key published conclusions challenges a long-held clinical assumption: that when depression lifts, cognitive symptoms improve along with it.
That did not happen in XanaCIDD. Improvements in depression and cognition were not correlated, according to the published findings. Patients whose mood improved did not consistently show parallel cognitive gains, and vice versa.
This dissociation has implications beyond Actinogen’s drug development program. It suggests that cognitive impairment in depression may not be a secondary symptom that resolves when mood resolves, but an independently driven biological process that requires separate targeting. If that finding is robust, it has potential consequences for how clinical trials in this population are designed and how physicians treat patients who recover from depression but remain cognitively impaired.
Prof. Michael Berk AO, an academic psychiatrist and co-author of the BJP paper, framed the finding in terms of the drug’s broader significance: "There remains a significant unmet medical need for therapies such as Xanamem that have a novel mechanism of action and can be safely combined with existing depression treatments," he said in the company’s announcement.
How the Drug’s Mechanism Explains the Unusual Timing
The durability of Xanamem’s antidepressant effect — growing stronger in the weeks after the drug was stopped — is not simply unexpected. It is mechanistically predictable.
Cortisol-related biological effects do not resolve the moment cortisol levels drop. When patients begin or stop chronic corticosteroid therapy such as prednisone, physicians expect the downstream biological effects to take weeks to normalize. Xanamem’s time course matches exactly that pattern: the drug gradually lowers intraneuronal cortisol during the six-week treatment, the affected biological pathways continue normalizing through the four-week follow-up, and the maximum antidepressant effect appears at the trough of that normalization — a timeline consistent with known cortisol biology.
Actinogen had previously confirmed, using positron emission tomography (PET) imaging, that 10 mg of Xanamem daily achieves substantial 11β-HSD1 enzyme occupancy in the brain — validating that the drug reaches its intended target. The clinical pharmacology paper confirming this was published in Clinical Pharmacology in Drug Development in February 2025.
What the Field Has Tried and Failed
The cortisol-depression hypothesis is not new, but translating it into clinical benefit has proven difficult. At least one prior 11β-HSD1 inhibitor — AbbVie’s ABT-384 — was evaluated in a Phase 2 multicenter trial for Alzheimer’s disease, comparing two dose levels against donepezil and placebo in mild to moderate Alzheimer’s patients, before being stopped early for futility.
A 2025 systematic review in the International Journal of Molecular Sciences examined clinical trials involving both ABT-384 and Xanamem’s prior Alzheimer’s work, concluding that they had produced mixed results without substantial cognitive improvements despite effective enzyme inhibition.
Actinogen itself has experienced prior setbacks. In 2019, the XanADu Phase 2 trial in mild Alzheimer’s disease failed to show statistically significant differences between Xanamem and placebo on cognitive endpoints — a result that led the company to redesign its Alzheimer’s program around biomarker-enriched patient selection.
The current XanaMIA trial differs from XanADu in one important way: participants must have elevated levels of pTau181 in their blood, a marker that identifies patients whose Alzheimer’s disease is likely to progress. Enriching for biological disease activity is expected to increase the signal-to-noise ratio compared with the earlier unselected population.
Separately, emerging research from 2026 suggests that the APOE4 genetic variant — the strongest known genetic risk factor for Alzheimer’s disease — may specifically upregulate 11β-HSD1 expression in the entorhinal cortex, a brain region affected early in Alzheimer’s pathology. If confirmed, that finding would suggest the drug may be most effective in APOE4 carriers — a path toward genotype-guided patient selection that could substantially improve the drug’s success probability in future trials.
Does This Drug Have a Chance in Alzheimer’s?
The depression data published in the British Journal of Psychiatry is strategically important to Actinogen’s Alzheimer’s program for two reasons.
First, it confirms that the 10 mg daily dose used in XanaMIA is a clinically active dose. A drug that does nothing in depression would raise questions about whether it is doing anything in the brain at all. The MADRS improvement removes that doubt.
Second, depression is common in Alzheimer’s patients, and antidepressant activity in that population may independently improve their quality of life and adherence — a secondary benefit the trial will capture.
The pivotal XanaMIA trial has enrolled 247 patients with mild to moderate, biomarker-confirmed Alzheimer’s disease across sites in Australia and the United States. The primary endpoint is the Clinical Dementia Rating Scale – Sum of Boxes (CDR-SB), the standard measure used in contemporary Alzheimer’s drug trials. An independent Data Monitoring Committee conducted a scheduled safety review on June 17, 2026, and recommended the trial continue without amendment. Final topline results from the 36-week randomized phase are expected in November 2026.
If the XanaMIA results are positive, Actinogen has received scientific advice from both the U.S. Food and Drug Administration and the European Medicines Agency on potential accelerated approval pathways — the FDA having signaled openness to reviewing applications supported by a single pivotal trial with adequate supporting evidence. The company outlined these regulatory discussions in its April 2026 business update.
Should the trial fail, Xanamem would face a difficult path forward. The drug remains an investigational product and is not approved for any use by the FDA or any other global regulatory authority.
Is Xanamem Available?
Xanamem (emestedastat) is not approved for any indication by the FDA or any global regulatory authority. It is an investigational product available only within clinical trials. The XanaMIA-DUR open-label extension allows participants who completed the XanaMIA randomized phase to continue receiving active Xanamem for up to 25 months — the most direct current access pathway. Members of the public cannot obtain Xanamem outside of a clinical trial setting.
Frequently Asked Questions
Why did Xanamem’s antidepressant effect peak four weeks after patients stopped taking it?
Cortisol biology operates on a slower timescale than serotonin or dopamine. When intraneuronal cortisol is chronically elevated — as it is in many depressed patients — the downstream biological damage takes time to accumulate, and the reversal of that damage takes time once cortisol levels drop. This is the same mechanism physicians observe when starting or stopping long-term corticosteroid therapies such as prednisone: the biological effects lag behind the drug’s presence or absence by weeks. Xanamem’s MADRS improvement growing through the four-week post-treatment observation period is consistent with exactly this cortisol biology timeline.
Why didn’t Xanamem improve cognition if it improved depression?
This is the trial’s most scientifically interesting finding. The British Journal of Psychiatry paper explicitly notes that improvements in depression and cognition were not correlated in XanaCIDD — patients who got better at depression did not consistently get better at cognition, and vice versa. This suggests that cognitive impairment in depression-with-cognitive-symptoms may be a biologically independent process from mood symptoms, not a secondary effect that resolves when mood resolves. The cognitive endpoint also suffered from an unexpectedly large placebo response, which compressed the statistical margin available for detecting a drug effect.
What happens in November 2026?
Actinogen expects to release topline results from the XanaMIA Phase 2b/3 Alzheimer’s disease trial, which has enrolled 247 patients with biomarker-confirmed mild to moderate Alzheimer’s disease and has been treating them for 36 weeks with Xanamem or placebo. The primary endpoint is the CDR-SB (Clinical Dementia Rating Scale – Sum of Boxes), the standard measure used to detect disease modification in Alzheimer’s trials. The independent Data Monitoring Committee has reviewed safety data and efficacy futility and recommended continuation; that recommendation does not predict a positive result, only that the trial is not already clearly failing. November 2026 will be the first definitive efficacy readout.
Can someone outside a clinical trial get access to Xanamem for treatment-resistant depression?
No. Xanamem is an investigational product not approved by the FDA or any global regulatory authority for any indication. The drug is currently available only to participants in Actinogen’s clinical trials. The XanaMIA-DUR open-label extension is open to participants who have completed the XanaMIA Alzheimer’s trial — it is not a general-access program for depression patients. No expanded access or compassionate use program for Xanamem in depression has been announced.
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