IUPAC: 2-(3,4,5-trimethoxyphenyl)ethan-1-amine · C₁₁H₁₇NO₃ · MW 211.26 g/mol · CAS 54-04-6
3,4,5-Trimethoxyphenethylamine. The archetypal phenethylamine psychedelic and the oldest psychedelic known to Western science (isolated by Heffter, 1897; synthesised by Späth, 1919). The principal alkaloid of peyote (Lophophora williamsii), San Pedro (Echinopsis pachanoi) and Peruvian torch. The template from which Shulgin built the entire 2C-x / DOx family in PIHKAL. Low affinity, high dose, long haul.
Mescaline is a serotonergic psychedelic whose defining action is agonism at the 5-HT2A receptor, coupling through Gq/11 → PLCβ → IP₃/DAG in layer-V cortical pyramidal neurons — the same final common pathway as LSD, psilocin and DMT. What sets mescaline apart is its scaffold. It is a bare phenethylamine: a benzene ring trimethoxylated at the 3,4,5 positions, joined by a two-carbon chain to a primary amine. It carries no indole — none of the fused bicyclic ring system that defines the tryptamines (DMT, psilocin) and ergolines (LSD).
That missing indole costs it dearly at the receptor. Tryptamines and ergolines exploit the indole/ergoline core for a tight, partly pre-organised fit; mescaline must bury a floppy, symmetric trimethoxyphenyl ring and pay a large binding penalty. The result is an affinity roughly 500–1000× weaker than LSD (Ki ~550 nM vs ~1 nM) and ~10–20× weaker than psilocin. This single number is the reason a mescaline dose is measured in hundreds of milligrams while an LSD dose is measured in micrograms.
Mescaline's protonated amine salt-bridges Asp155(3.32) while the trimethoxyphenyl ring packs against the aromatic cage (Phe339/Phe340) and Ser159/Ser239, stabilising the active, Gq-coupled conformation and driving IP₃/DAG in cortical pyramidal neurons.
Mescaline is actually slightly more potent at 5-HT2C (Ki ~300 nM) than at 5-HT2A. 2C agonism shapes mood, appetite suppression and some of the interoceptive/anxiogenic tone of the come-up.
Sub-micromolar Ki at every serotonin site means receptor occupancy only becomes meaningful at plasma concentrations reached by 200–400 mg oral doses — three to four orders of magnitude more drug than an ergoline needs.
Agonist at 5-HT2B (Ki ~795 nM). Irrelevant to a single experience, but 5-HT2B is the valvulopathy receptor — the reason chronic high-frequency dosing of any 2B agonist carries a theoretical cardiac-valve risk (cf. fenfluramine).
The unhindered primary amine makes mescaline a substrate for monoamine oxidase, which oxidatively deaminates it to an inactive carboxylic acid. This is both its main clearance route and the basis of a dangerous MAOI interaction.
Like other 5-HT2A psychedelics, mescaline down-regulates the receptor with repeat dosing and is cross-tolerant with LSD and psilocybin. Tolerance builds within days and resets over ~1–2 weeks; there is no compulsive redosing and no physical dependence.
Mescaline is the pharmacophore Alexander Shulgin dissected in PIHKAL. Ring-methylation of the α-carbon yields the amphetamine analogs (the DOx series, e.g. DOM, DOI); swapping the 4-methoxy for larger lipophilic groups and adding an N-benzyl yields the 2C-x and NBOMe families — all of which claw back the affinity mescaline lacks. Mescaline itself remains the low-potency, long-duration, remarkably gentle parent of the class.
Mescaline is well absorbed orally and — unusually for a psychoactive amine — a large fraction of the dose is excreted unchanged in the urine. Classic human balance studies (Charalampous et al., 1966) recovered the great majority of a dose in urine, of which roughly 55–60% was parent mescaline and ~27–30% the inactive acid metabolite. The slow, ceiling-shaped plasma curve — peak at ~2 h, effects spanning 10–12 hours — is a property of the molecule's leisurely clearance, not of any active metabolite prolonging the experience.
Metabolism cascade: The primary amine is oxidatively deaminated by monoamine oxidase to an aldehyde, then oxidised by aldehyde dehydrogenase to the inactive acid. A parallel minor route N-acetylates the amine; the rest simply leaves via the kidney.
3,4,5-Trimethoxyphenylacetic acid (TMPAA, marked as the terminal node) is pharmacologically inert and is the principal identified metabolite. Because clearance leans on MAO and the kidney rather than on CYP2D6, mescaline does not share the CYP2D6-poor-metaboliser exposure lottery that complicates MDMA and many tryptamines. The corollary is the reverse hazard: anything that inhibits MAO removes mescaline's main off-switch (see Harm Reduction).
Note that human PK for mescaline is sparse and rests largely on mid-20th-century studies and a handful of modern self-report/observational reports; the numbers above are best-available estimates, and parameters such as volume of distribution and plasma protein binding are not well characterised. Where a value is uncertain it is presented as a range, not a false precision.
5-HT2A receptors are densest on the apical dendrites of layer-V pyramidal neurons in cortex. Agonism there increases cortical excitability and glutamatergic tone, desynchronises ongoing activity, and — in current predictive-processing framing — relaxes the weight of high-level priors on perception and self-modelling. The phenomenology of mescaline follows the classic psychedelic template, but with its own texture: a slow, bodily, warmly emotional come-up; saturated colour and richly geometric eyes-closed visuals; and a long, plateau-shaped arc.
Layer-V pyramidal 5-HT₂A agonism raises glutamate release onto local and thalamocortical circuits, driving visual-cortex hyperexcitability (geometric/organic imagery), synaesthesia-like binding, and the loosening of habitual conceptual frames. This is the shared engine of all classic psychedelics; occupancy tracks the subjective intensity.
Disrupted thalamic and claustral filtering reduces the brain's ability to gate and compress incoming signals — sensory streams that are normally suppressed reach awareness. At high doses this destabilises the self-model, producing the boundary-dissolution and unity states characteristic of a full mescaline experience.
Mescaline produces mild sympathetic activation (mydriasis, modest tachycardia, tremor, appetite suppression) but little direct mesolimbic dopamine drive. Reinforcement is low, addiction potential is negligible, and rapid tolerance further discourages compulsive use — the pharmacological opposite of a stimulant.
Peyote has been used ceremonially in Mesoamerica for millennia and is the sacrament of the Native American Church, which holds a specific U.S. legal exemption. Wild Lophophora is slow-growing and increasingly threatened by over-harvest and habitat loss — an ecological and cultural-sovereignty issue that sits alongside the pharmacology. San Pedro / Peruvian torch (Trichocereus) are faster-growing and legal to cultivate as ornamentals in many jurisdictions. Set, setting and preparation are not decoration here: a 10–12 h journey rewards planning and punishes carelessness.
Interestingly, at matched intensity mescaline is often described as more emotionally open and less "electric" or anxiogenic than LSD — differences that may reflect its balanced 5-HT2A/2C profile, its lack of the ergoline's promiscuous dopaminergic and long-residence-time pharmacology, and simply the gentler kinetics of a slowly-cleared, slowly-onsetting molecule.
Evidence-based, non-moralistic. Mescaline has a high physiological therapeutic index — deaths from mescaline alone are very rare — but the long duration, prominent nausea, and one genuinely dangerous drug interaction demand respect and planning.
| Target | Affinity | Rel. | Mechanism |
|---|---|---|---|
|
5-HT2C
Serotonin 2C receptor (HTR2C)
|
Ki = 303 nM
human · [¹²⁵I]DOI
|
Agonist | |
|
5-HT2A
Serotonin 2A receptor (HTR2A)
|
Ki = 551 nM
human · rat 360–5500 nM
|
Agonist | |
|
5-HT2B
Serotonin 2B receptor (HTR2B)
|
Ki = 795 nM
human
|
Agonist | |
|
5-HT1A
Serotonin 1A receptor
|
Ki = 6,900 nM
rat · [³H]-8-OH-DPAT
|
Weak agonist |