3,4,5-trimethoxyphenethylamine (mescaline) induces mind-altering effects in humans mainly through interaction with the 5-HT2A receptor. Mescaline is primarily metabolized into 3,4,5-trimethoxyphenylacetic acid (TMPAA) and additionally into several minor metabolites. This study aimed to identify the specific metabolic enzymes involved and investigate the pharmacokinetics of mescaline and metabolites in humans.

The role of cytochrome P450 (CYP) enzymes was assessed in vitro utilizing human liver microsomes (HLM) and recombinant CYP enzymes. Additionally, the involvement of monoamine oxidases (MAOs) was examined. Mescaline’s metabolism in humans was explored by analyzing pharmacokinetic plasma samples obtained from 32 healthy volunteers who received oral doses of mescaline (100–800 mg). Samples were analyzed using LC-MS/MS.

Mescaline was not metabolized in the presence of HLM. However, recombinant CYP2D6 enzymes produced small amounts (<10 nM) of 3-desmethyl and 4-desmethyl mescaline but did not generate TMPAA or N-acetyl mescaline (NAM). Plasma sample analysis confirmed TMPAA as a major in vivo metabolite. Minor in vivo pathways included acetylation to NAM and demethylation to either 3-desmethyl or 4-desmethyl mescaline. Surprisingly, TMPAA was not found following incubations with MAO enzymes, indicating other involved enzymes. For instance, substantial fluctuation in NAM concentration suggests a potential involvement of polymorphic enzymes such as N-acetyl transferases.

In conclusion, TMPAA emerged as the primary in vivo metabolite, alongside minor metabolites like NAM and demethylated mescaline. Recombinant CYP2D6 produced small quantities of demethylated mescaline, confirming its involvement in this metabolic process. However, our in vitro results suggest that enzymes other than CYPs and MAOs are involved in mescaline’s metabolism.