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Bretisilocin, also known by its developmental code name GM-2505 and as 5-fluoro- N-methyl- N-ethyltryptamine ( 5F-MET or 5-fluoro-MET), is a serotonergic psychedelic of the tryptamine family which is under development for the treatment of major depressive disorder. It is an analogue of dimethyltryptamine (DMT) and is the 5-fluorine derivative of methylethyltryptamine (MET). Bretisilocin's route of administration is intravenous infusion.
The drug acts as a potent and well-balanced serotonin 5-HT2A and 5-HT2C receptor agonist, serotonin 5-HT2B receptor antagonist, and serotonin releasing agent. It produces psychedelic-like effects in animals and similarly produces robust effects in humans. The duration of bretisilocin is 60 to 90minutes and is intermediate between the durations of DMT and psilocybin. It has been regarded by its developer as an improvement of DMT.
Bretisilocin is under development by Gilgamesh Pharmaceuticals. As of June 2025, it is in phase 2 for the treatment of major depressive disorder.
The affinity (Ki) of bretisilocin for the serotonin 5-HT2A receptor was 4.9nM with DOI as the radioligand and 140nM with ketanserin as the radioligand. Its () values were 15.0–20.6nM (80.6–87.6%) at the serotonin 5-HT2A receptor and 9.5nM (85.1%) at the serotonin 5-HT2C receptor, whereas its at the serotonin 5-HT2B receptor was 5.8nM. It showed much higher maximal efficacy at the serotonin 5-HT2A receptor than its parent compound MET ( = 87.6% vs. 36.2%, respectively). Bretisilocin showed very weak activity at the serotonin 5-HT1A receptor ( = 16,918nM, = 83.0%). In addition to its actions at the serotonin 5-HT2 receptors, it is a partial serotonin releasing agent in rat brain , with an of 8.4–15.7nM and an of 66.8–71.4%. Bretisilocin is also a serotonin reuptake inhibitor to a much weaker extent ( = 418.9nM). Additional values have also been published.
Bretisilocin is related to DMT and is considered by its developer to be an improved version of DMT. It also induces more serotonin release than DMT, which may provide it with more entactogen-like qualities compared to DMT. Bretisilocin produces the head-twitch response, a behavioral proxy of psychedelic effects, in rodents. It shows antidepressant-like effects in rodents. The drug dose dependence produces hypolocomotion in rodents similarly to many other serotonergic psychedelics. (2025). 9783662558782 ISBN 9783662558782 Likewise, it produces anti-obsessional effects in the form of reduced marble burying in rodents. Bretisilocin does not produce conditioned place preference (CPP) in rodents, suggesting lack of reinforcing properties.
"bretisilocinum bretisilocin N-ethyl-2-(5-fluoro-1H-indol-3-yl)-N-methylethan-1-amine serotonin (5-HT2A) receptor agonist" It is also known by its developmental code name GM-2505.
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