• Gilgamesh's lead asset, bretisilocin (GM-2505), is a potential best-in-class psychedelic compound currently in Phase 2 development for the treatment of major depressive disorder (MDD).
• Bretisilocin is a novel, short-acting serotonin (5-HT)2A receptor agonist and 5-HT releaser.

NORTH CHICAGO, Ill. and NEW YORK, Aug. 25, 2025 /PRNewswire/ -- AbbVie (NYSE: ABBV) and Gilgamesh Pharmaceuticals Inc. ("Gilgamesh") today announced a definitive agreement under which AbbVie will acquire Gilgamesh's lead investigational candidate, currently in clinical development for the treatment of patients with moderate-to-severe major depressive disorder (MDD).

Psychedelic compounds, including 5-HT_2A receptor agonists, have gained recognition as potential treatments for mental health disorders, such as MDD, because of their demonstrated rapid, robust and durable antidepressant effects. However, existing agents in this class are hampered by their long duration of psychoactive experience.

Bretisilocin, a 5-HT_2A receptor agonist and 5-HT releaser, is a novel, next-generation psychedelic compound designed to address development challenges observed within this class of compounds. Bretisilocin has been shown to exert a shorter duration of psychoactive experience, while retaining an extended therapeutic benefit.

Positive topline results from a Phase 2a study of bretisilocin in MDD were recently announced, demonstrating a clinically impactful and statistically significant reduction in severity of depressive symptoms versus low dose active comparator, as measured by the Montgomery-Åsberg Depression Rating Scale (MADRS) total score. At Day 14, a single dose (10mg) of bretisilocin demonstrated robust antidepressant effect with a -21.6 point change from baseline in MADRS total score compared to a -12.1 point change from baseline for the low dose (1mg) active comparator (p = 0.003). Bretisilocin was well tolerated with no serious adverse events.

"The field of psychiatry represents one of the most challenging areas in medicine, with a significant need for innovative solutions," said Roopal Thakkar, M.D., executive vice president, research and development and chief scientific officer, AbbVie. "This acquisition underscores our commitment to broadening and enhancing psychiatric care by investing in novel treatment approaches with the potential to reach patients for whom other treatments have been ineffective. We look forward to advancing bretisilocin to late-stage clinical development."

"AbbVie's leadership in neuroscience and commitment to advancing innovative treatments make them the ideal partner to advance bretisilocin rapidly forward while enabling Gilgamesh to continue pursuing our broader mission of developing novel, transformative therapies for complex mental health and neurological conditions," said Jonathan Sporn, M.D., chief executive officer at Gilgamesh Pharmaceuticals.   

Under the terms of the agreement, AbbVie will acquire Gilgamesh's bretisilocin program for up to $1.2 billion, inclusive of an upfront payment and development milestones. Additionally, as part of the transaction, Gilgamesh will spin off a new entity that will operate under the name Gilgamesh Pharma Inc. to hold its employees and other programs, including its oral NMDA receptor antagonist blixeprodil (GM-1020), cardio-safe ibogaine analog, M1/M4 agonist program and existing collaboration with AbbVie. The transaction is subject to customary closing conditions.

This transaction builds upon AbbVie and Gilgamesh's 2024 collaboration and option-to-license agreement to advance the development of next-generation therapies for the treatment of psychiatric disorders. This option-to-license remains in effect and will be transferred to Gilgamesh Pharma Inc. in connection with the spin-out.

Advisors

For AbbVie, Covington & Burling LLP is acting as legal counsel. For Gilgamesh, Centerview Partners LLC is acting as exclusive financial advisor and Ropes & Gray LLP is acting as legal counsel. 

About AbbVie

AbbVie's mission is to discover and deliver innovative medicines and solutions that solve serious health issues today and address the medical challenges of tomorrow. We strive to have a remarkable impact on people's lives across several key therapeutic areas including immunology, oncology, neuroscience and eye care – and products and services in our Allergan Aesthetics portfolio. For more information about AbbVie, please visit us at www.abbvie.com. Follow @abbvie on LinkedIn, Facebook, Instagram, X (formerly Twitter) and YouTube.

About Gilgamesh Pharmaceuticals

Gilgamesh Pharmaceuticals is a clinical-stage neuroscience biotech developing innovative, best-in-class new chemical entities that transform the treatment paradigm of psychiatric diseases, moving away from symptom management towards rapid-acting and durable therapies. Gilgamesh designs therapies acting through precedented mechanisms, which are optimized for safety, efficacy, and patient access. Gilgamesh is advancing a diverse portfolio of programs, including blixeprodil (GM-1020), an oral NMDA receptor antagonist that is completing a Phase 2a study in Major Depressive Disorder in 2025. Learn more about the company's therapeutic pipeline at https://www.gilgameshpharmaceutical.com/. Follow Gilgamesh Pharmaceuticals on LinkedIn and X.

Forward-Looking Statements 

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