Almost a month after rumours surfaced that AbbVie was weighing a $1-billion bid for Gilgamesh Pharmaceuticals, the company announced Monday it will acquire the neuroscience biotech's lead asset — the psychedelic depression candidate bretisilocin (GM-2505) — in a deal worth up to $1.2 billion.Bretisilocin is a serotonin 5-HT2A receptor agonist and 5-HT releaser currently in mid-stage development. Unlike psilocybin or LSD, which can keep patients in a psychoactive state for six to 10 hours, "bretisilocin has been shown to exert a shorter duration of psychoactive experience, while retaining an extended therapeutic benefit," the companies said in a joint release.Topline Phase IIa results suggest the drug may indeed deliver. In patients with moderate-to-severe major depressive disorder, a single 10-mg dose reduced Montgomery-Åsberg Depression Rating Scale (MADRS) scores from baseline by 21.6 points after two weeks, compared with a 12.1-point reduction in patients given a low-dose active comparator. The antidepressant effect emerged within 24 hours and was durable after just two treatment sessions, Gilgamesh reported in May. Bretisilocin was also generally well tolerated, with no serious adverse events reported.Clinicians see the drug's shorter-acting profile as a potential advantage. "This compound acts in just a couple of hours, so that would position it to really compete well against other psychedelics that are further along but longer-acting," Brian Barnett, clinical director of the psychiatric treatment resistance program at Cleveland Clinic, recently said in an interview with FirstWord. He also suggested bretisilocin could prove to be "a nice alternative" to Johnson & Johnson's Spravato (esketamine), with more durable benefit.Monday's deal includes an upfront payment and development milestones. As part of the transaction, Gilgamesh will also spin out a new entity that will operate under the name Gilgamesh Pharma to hold its employees and remaining programmes, including its oral NMDA receptor antagonist blixeprodil (GM-1020), cardio-safe ibogaine analogue (GM-3009), M1/M4 agonist programme and non-hallucinogenic neuroplastogens, already the centre of an existing $2-billion tie-up with AbbVie (see – Spotlight On: Neuroplastogens hit the mainstream in 2024. What's next for trip-less psychedelics?).