4-AcO-DMT

4-Acetoxy-N,N-dimethyltryptamine (4-AcO-DMT), also designated O-acetylpsilocin and psilacetin, is a synthetic indole ester first prepared by Albert Hofmann and Franz Troxler at Sandoz Laboratories in 1963 as part of a systematic exploration of psilocin ester derivatives (U.S. Patent 3,075,992). The compound is the O-acetyl ester of psilocin (4-hydroxy-N,N-dimethyltryptamine), the principal psychoactive metabolite of psilocybin, and functions as a prodrug that undergoes rapid enzymatic deacetylation to liberate psilocin in vivo. In human plasma, hydrolysis to psilocin proceeds to greater than 99.9 percent completion within approximately five minutes, and in pooled human liver microsomes, at least fifteen metabolites have been identified, with psilocin as the most abundant hydrolysis product and additional biotransformations including hydroxylation, N-demethylation, oxidative deamination, and phase II glucuronidation. The compound displays low intrinsic potency at the human 5-HT2A receptor in vitro (EC50 approximately 103 nM, Emax approximately 79 percent of the serotonin maximum), approximately ten- to twenty-fold lower than psilocin (EC50 approximately 2.4 nM, Emax approximately 98 percent), consistent with the prodrug hypothesis that the pharmacological activity of 4-AcO-DMT is predominantly mediated through in vivo conversion to psilocin rather than through direct receptor interaction of the parent compound.

In vivo validation in C57BL/6J mice demonstrated that intraperitoneal psilacetin fumarate at equimolar doses produces approximately 70 percent of the peripheral psilocin exposure generated by psilocybin, with overlapping 95 percent confidence intervals for potency in head-twitch response, hypolocomotion, and hypothermia assays. These findings, published by Jones et al. (2024) in Frontiers in Psychiatry, provided the first direct pharmacokinetic confirmation of the long-standing assumption that psilacetin functions as a psilocin prodrug in vivo and established psilacetin fumarate as a viable research substitute for psilocybin in mechanistic psychedelic studies. The modestly lower peripheral psilocin exposure may confer a differentiated pharmacokinetic profile with potential implications for peripheral side-effect burden, although this hypothesis has not been tested in human clinical studies.

No clinical trials of 4-AcO-DMT have been conducted in humans as of the date of this monograph. No toxicological studies have formally established a toxic dose, a therapeutic index, or a long-term safety profile. The compound is not scheduled under the United Nations Convention on Psychotropic Substances and is not explicitly controlled under United States federal drug schedules, although it may be subject to prosecution under the Federal Analogue Act when intended for human consumption. It is a Class A substance in the United Kingdom and a Schedule 9 prohibited substance in Australia. David E. Nichols and Stewart Frescas at Purdue University published an improved synthesis in 1999, proposing psilacetin as a more economical and accessible alternative to psilocybin for scientific research. The compound crystallizes readily as the fumarate salt, which is substantially more stable than psilocin itself and is the standard research-grade form. This monograph reviews the chemistry, synthesis, and structural characterization of 4-AcO-DMT; the prodrug pharmacology and in vitro serotonin receptor activity; the metabolic and pharmacokinetic profile as characterized in microsomal and in vivo studies; the preclinical evidence base; the current absence of clinical data; sourcing, reconstitution, and handling considerations; stack interactions; the adverse-event and safety signal; and a structured comparative assessment of five psilocin prodrug and psychedelic tryptamine alternatives against 4-AcO-DMT on five competency standards.