AbbVie agreed to acquire bretisilocin, an investigational psychedelic therapy for major depressive disorder, from privately held Gilgamesh Pharmaceuticals in a transaction worth as much as $1.2 billion. The consideration comprises an undisclosed upfront payment and development-linked milestones. Bretisilocin, also known as GM-2505, is a short-acting 5-HT2A receptor agonist designed to deliver rapid antidepressant effects with a briefer psychoactive experience than classic psychedelics such as psilocybin or LSD. Early and mid-stage studies have suggested durable symptom relief, and AbbVie plans to advance the compound into late-stage trials. The purchase deepens AbbVie’s push into neuroscience after more than $20 billion in recent deal-making aimed at offsetting revenue lost to generic competition for Humira. Analysts estimate the market for psychedelic-based psychiatric treatments could reach about $50 billion, yet large pharmaceutical companies have so far moved cautiously amid regulatory uncertainties. Gilgamesh will spin off its other research programs—including candidates for anxiety, PTSD and schizophrenia—into a new entity, Gilgamesh Pharma, while AbbVie retains option rights to future compounds under an existing collaboration between the two companies.