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| Other names | GM-2505; GM2505; 5-Fluoro-N-methyl-N-ethyltryptamine; 5F-MET; 5-F-MET; 5-Fluoro-MET |
| Routes of administration | Intravenous[1][2][3][4] |
| Drug class | Serotonergic psychedelic;Hallucinogen;Serotonin5-HT2A and5-HT2C receptoragonist;Serotonin5-HT2B receptorpartial agonist orantagonist;Serotonin releasing agent |
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| Pharmacokinetic data | |
| Onset of action | 10–20 minutes (peak)[2] |
| Eliminationhalf-life | 45 (40–50) minutes[2][3] |
| Duration of action | 60–90 minutes[2][5] |
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| Chemical and physical data | |
| Formula | C13H17FN2 |
| Molar mass | 220.291 g·mol−1 |
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Bretisilocin, also known by its developmental code nameGM-2505 and as5-fluoro-N-methyl-N-ethyltryptamine (5F-MET or5-fluoro-MET), is aserotonergic psychedelic of thetryptamine family which is under development for the treatment ofmajor depressive disorder.[1][6][2][3] It is ananalogue ofdimethyltryptamine (DMT) and is the 5-fluorinatedderivative ofmethylethyltryptamine (MET).[7] Bretisilocin'sroute of administration isintravenous infusion.[1][2][3][4]
The drug acts as apotent and well-balancedserotonin5-HT2A and5-HT2C receptoragonist, serotonin5-HT2B receptorpartial agonist orantagonist, andserotonin releasing agent.[2][8][7][9] It produces psychedelic-like effects in animals and similarly produces robusthallucinogenic effects in humans.[8][3] Theduration of bretisilocin is 60 to 90 minutes and is intermediate between the durations of DMT andpsilocybin.[5][10][4][11][7][2] It has been regarded by its developer as an improvement of DMT.[11]
Bretisilocin was first described in the literature by 2022.[8][9] It is under development byGilgamesh Pharmaceuticals.[1] As of June 2025, the drug is inphase 2clinical trials for the treatment ofmajor depressive disorder.[1] Bretisilocin was acquired from Gilgamesh Pharmaceuticals byAbbVie in a deal worth up to $1.2 billion in August 2025.[12][13]
Bretisilocin, given byintravenous injection, produces thresholdpsychedelic effects at doses of 1 mg and 3.3 mg, has an optimal dose range of 10 to 15 mg, and produces particularly intense effects at a dose of 20 mg.[2] The drug's effects at doses of 15 to 20 mg were described as equivalent to or greater than those of 30 mgpsilocybin or 100 to 200 μgLSD based onrating scales.[2] The 20 mg dose of bretisilocin was associated with more challenging experiences includinganxiety,cognitive impairment, and dread ofego dissolution, which led to selection of a lower optimal dose range of 10 to 15 mg.[2] Compared to other psychedelics like psilocybin and LSD, bretisilocin has a much shorterduration, but is longer-lasting thanDMT.[2][10][4][7] Its duration is about 60 to 90 minutes, whereas psilocybin has a duration of multiple hours and DMT has a duration of as short as 10 minutes.[2][5][11] The psychedelic effects of bretisilocin are generally resolved by approximately 2 hours after administration, but have been found to last up to 4 to 6 hours in some individuals.[2] Peak effects occur about 10 to 20 minutes following injection.[2]
The drug, administered intravenously in clinical studies, produces effects in humans including "altered states of consciousness, altered visualdepth perception,abnormal thinking,euphoric mood,feeling drunk, feeling ofbody temperature changes,relaxation,sensory processing disorder (including intense visual effects with color changes),sensory overload, andtime perception altered".[2][3][4] The subjective effects of bretisilocin were described as very robust and consistent in strength with the effects of other psychedelics including LSD, DMT, and psilocybin as have been reported in clinical studies.[2][3][4]
Side effects of bretisilocin include acutesensory processing disorder,altered state of consciousness,abnormal thinking,euphoric mood,fatigue, and small increases inheart rate andblood pressure, among others.[2][3][4] Adverse effects like fatigue andheadache occur after thepsychedelic experience and can persist for up to 24 hours after administration.[2]
Bretisilocin acts as apotent and well-balancedserotonin5-HT2A and5-HT2C receptoragonist, serotonin5-HT2B receptorantagonist, andserotonin releasing agent.[2][8][9] In another study however, it was a moderate-efficacypartial agonist of the serotonin 5-HT2B receptor.[9] The drug appears to have negligible activity as a serotonin5-HT1A receptor agonist.[8] However, another study found that it was a serotonin 5-HT1A receptorfull agonist, with anEC50Tooltip half-maximal effective concentration at this receptor that was about 44-fold lesspotent than at the serotonin 5-HT2A receptor.[9]
Theaffinity (Ki) of bretisilocin for the serotonin 5-HT2A receptor was 4.9 nM withDOI as theradioligand and 140–191 nM withketanserin as the radioligand.[2][8] ItsEC50Tooltip half-maximal effective concentration (EmaxTooltip maximal efficacy) values were 15.0–20.6 nM (80.6–87.6%) at the serotonin 5-HT2A receptor and 9.5 nM (85.1%) at the serotonin 5-HT2C receptor, whereas itsIC50Tooltip half-maximal inhibitory concentration at the serotonin 5-HT2B receptor was 5.8 nM.[2][8] It showed much higherefficacy at the serotonin 5-HT2A receptor than itsparent compoundMET (Emax = 87.6% vs. 36.2%, respectively).[7] Bretisilocin showed very weak activity at the serotonin 5-HT1A receptor (EC50 = 16,918 nM,Emax = 83.0%).[2][8][7] In addition to its actions at the serotonin5-HT2 receptors, it is apartial serotonin releasing agent in rat brainsynaptosomes, with anEC50 of 8.4–15.7 nM and anEmax of 66.8–71.4%.[2][8][7] Bretisilocin is also aserotonin reuptake inhibitor to a much weaker extent (IC50 = 418.9 nM).[7] Additional values have also been published.[2][9]
Bretisilocin is related toDMT and is considered by its developer to be an improved version of DMT.[2][11] It also induces more serotonin release than DMT, which may provide it with moreentactogen-like qualities compared to DMT.[2][11] Bretisilocin produces thehead-twitch response, a behavioral proxy of psychedelic effects, in rodents.[2][8][3][7] It showsantidepressant-like effects in rodents.[8][10] The drugdose-dependently produceshypolocomotion in rodents similarly to many other serotonergic psychedelics.[7][14] Likewise, it producesanti-obsessional effects in the form of reducedmarble burying in rodents.[7] Bretisilocin does not produceconditioned place preference (CPP) in rodents, suggesting lack ofreinforcing properties.[7]
Thepharmacokinetics of bretisilocin have been studied.[2][3] Thetime to peak concentrations withintravenous injection is 10 to 20 minutes.[2] Itselimination half-life is approximately 45 minutes (range 40 to 50 minutes).[2][3]
Bretisilocin, also known as 5-fluoro-N-methyl-N-ethyltryptamine, is asubstituted tryptaminederivative.[7] It is a derivative ofdimethyltryptamine (DMT) andmethylethyltryptamine (MET) as well as of5-fluorotryptamine (5-FT).[5][7]
Someanalogues of bretisilocin include5-fluoro-DMT,5-fluoro-DET,5-fluoro-EPT,5-chloro-DMT,5-bromo-DMT,5-fluoro-AMT,5-fluoro-AET,5-MeO-MET, and7-F-5-MeO-MET, among others.
Bretisilocin was first described in thescientific literature by at least 2022.[8][9]
Bretisilocin is thegeneric name of the drug and itsINNTooltip International Nonproprietary Name.[15] It is also known by its developmental code nameGM-2505.[1][8][3]
Bretisilocin is under development as a potentialpharmaceutical drug byGilgamesh Pharmaceuticals.[1] As of June 2025, it is inphase 2clinical trials for the treatment ofmajor depressive disorder.[1] Aphase 2a trial of bretisilocin for major depressive disorder has been completed and theefficacy andsafety data for the trial have been released.[1][16][17][18] The drug has since been acquired from Gilgamesh Pharmaceuticals byAbbVie.[12][13]
Gilgamesh is also working on GM-2505, a 5-HT2A agonist that is structurally related to psilocybin and DMT. GM-2505 completed a phase 1 trial late last year and should enter phase 2 for major depressive disorder this year. Its psychedelic effect lasts 60 to 90 minutes — long enough for patients to "explore the altered state of consciousness that might be needed for long-term durable efficacy," Krugel says, yet within a timeframe that is manageable for healthcare systems. "Personally, I believe that the hallucinogenic effects are an important component, as multiple hallucinogenic compounds have demonstrated durable, transformational changes from a single dose in human studies," he adds.
GM-2505 is a dual-acting compound with both agonist activity at 5-HT 2A receptors and a releaser of 5-HT. [...]
