Mescaline

What it is

Mescaline is a small molecule, 3,4,5-trimethoxyphenethylamine, in the phenethylamine family [8] [11]. Reviews describe a consensus that classic psychedelics, including the tryptamines psilocybin and DMT, act as agonists or partial agonists at the serotonin 2A receptor, a docking site on brain cells that serotonin normally uses [9], and the human data below point to that receptor for mescaline too [2].

Two cacti are most associated with it. Peyote, Lophophora williamsii, is native to the Chihuahuan Desert, recorded by the IUCN Red List in seven Mexican states and in Texas [16]. San Pedro, Echinopsis pachanoi, is a columnar cactus from South America, and several related cacti also contain mescaline [5] [13]. A 2023 Canadian study described a near-complete peyote pathway from tyrosine, in a clonal commercial line that makes relatively little mescaline, so it does not describe a typical plant [14].

A cactus is not a standardized product. Fourteen Echinopsis taxa and cultivars tested by one method all contained mescaline, from 0.053 to 4.7 percent of dry weight [13], and a Korean forensic team reported L. williamsii plants that contain none [15]. Any comparison of studies starts with asking what was actually in the plant.

What is known

The short version. Controlled evidence in healthy adults comes from two trials at the University Hospital Basel, about fifty people in total. Mescaline produced a state that could not clearly be separated from LSD or psilocybin once the intensity was matched. It lasted longer than either, produced more nausea and more next-day complaints, and raised blood pressure and heart rate moderately. No controlled study has yet asked whether it changes anything in healthy adults weeks or months afterward, and every claim about lasting change rests on surveys.

The Basel trials

The first trial compared mescaline directly with LSD and psilocybin. Thirty-two healthy adults each attended four 25-hour hospital sessions covering mescaline, LSD, psilocybin and placebo in random, double-blind order [1]. Although people with major psychiatric disorder, a chronic physical illness, or more than ten lifetime uses of a psychedelic were excluded, 63 percent had used a psychedelic before, 69 percent had used MDMA, and only five of the 32 had never used an illicit drug other than cannabis [1].

The design has a wrinkle that matters. The team first gave mescaline at a lower strength, found it probably weaker than the comparators, and raised it for the second 16 participants, so the two strengths were compared between different people, without randomization or blinding [1]. At the higher strength, mescaline, LSD and psilocybin did not differ significantly in peak ratings on any of four scales. The authors found no evidence of qualitative differences, saw differences that depended on strength rather than substance, and wrote that their instruments may have missed subtle differences [1]. The trial was funded by the Swiss National Science Foundation, the hospital and Definium Therapeutics (formerly Mind Medicine Inc.). The senior author is a consultant to that company, which the paper says took no part in the design or publication, and the later Basel papers carry the same funding statement [1] [2] [3] [4].

What did differ was time. Subjective effects lasted a mean of 11.1 hours for mescaline (range 6 to 22), 8.2 hours for LSD and 4.9 hours for psilocybin, with a slower rise [1]. Blinding was imperfect for the higher mescaline strength, which 53 percent of participants identified correctly during the session and 81 percent after the study [1].

The second trial from the same group asked what mescaline acts on, in sixteen healthy adults across six sessions: placebo, four strengths of mescaline spanning an eightfold range, and the highest strength combined with ketanserin, a serotonin 2A receptor blocker [2]. Ketanserin cut the effects of the highest strength down to the level of the two lowest, pointing to the serotonin 2A receptor as the main route, though it was given at the same moment as mescaline rather than beforehand, so some early effects may have arrived before the blocker did [2]. A pharmacokinetic paper from the same group reports that 17 people were enrolled and one withdrew after distress during the first session at the highest strength, so the 16 are those whose data entered the within-person comparisons [4].

Basel also pooled the safety data from both trials (48 participants, 96 administrations). Systolic blood pressure stayed below 180 mmHg in every participant, with a highest reading of 166. Diastolic pressure went above 100 mmHg in 6 percent of administrations (highest 105), heart rate above 100 beats per minute in 3 percent (highest 108), and body temperature above 38 degrees Celsius in 5 percent (highest 39.0). Kidney function, liver function and blood counts remained normal. Nausea limited the highest strengths, and "flashbacks" were reported by two participants, after 2 percent of administrations, with none reporting a lasting change in perception [3]. About 53 percent of the dose was recovered in urine as unchanged mescaline, which indirectly suggests an oral bioavailability of at least 53 percent, an estimate that would need an intravenous dose to confirm [4].

What people reported after using it outside a laboratory

The largest dataset on naturalistic use is an anonymous online survey run in 2019 and advertised online. Of 2,025 people who clicked an advertisement, 788 consented and 452 gave valid answers, mostly white and male [5]. Respondents described their single most memorable mescaline experience, with San Pedro for 48 percent, peyote for 22 percent, and synthetic or extracted mescaline for the rest. Sixty percent used it less than once a year, 74 percent were motivated by spirituality or a wish to connect with nature, and 78 percent generally used it without anyone overseeing, 72 percent for the memorable experience itself [5].

Respondents rated mystical-type effects as moderate and challenging effects as very slight, and between 28 and 35 percent counted the experience among the five most meaningful of their lives. None reported seeking medical attention [5]. Ratings of the acute effects did not differ by source, although three items about lasting effects were slightly higher for peyote than for extracted mescaline, and the peyote group reported taking it more times in the memorable session [5]. Fewer than ten respondents identified as Native American or Indigenous, and the authors say historical mistrust of Western research is a likely reason [5].

A second paper reports that, among respondents with a past psychiatric condition, 68 to 86 percent said it improved after the memorable experience. Both papers describe one sample, with identical recruitment counts and demographic shares, so they are not independent confirmation, and they disagree on some figures: past depression is 44 percent in the first paper and 41 percent in the second, past anxiety 49 and 46 percent, and improvement in alcohol problems 67 and 76 percent, without explanation [5] [6]. The history was a single yes, no or not sure question, not a validated instrument, so these are self-reported histories and not diagnoses [6]. Three authors of the first paper are board members of the Source Research Foundation, which the paper says had no role in the work, and the second paper lists authors from the same foundation [5] [6].

For Metanoia's purposes these results carry four limits. Half of the sample reported past anxiety (49 percent) or depression (44 percent), so it is not a sample of healthy adults [5]. Everything is retrospective self-report, and an experience may be remembered as memorable because the person improved [5]. People who had a bad time may have been less likely to answer, and a cross-sectional survey cannot show that mescaline caused anything [5].

Long-term use inside a religious tradition

One older study of Navajo members of the Native American Church who regularly took peyote found no significant deficits on memory and executive-function tests against a low-use group. The authors state that this may not generalize to people who use hallucinogens illicitly, and a cross-sectional design cannot separate effects of peyote from differences in who joins the church [7].

Reviews and animal work

A 2026 systematic review screened 2,770 references, found 66 that met its criteria, and could analyze only 10. Reports in those papers included improvements on depression scales and in well-being, and also hypertension, headache, nausea and vomiting, and the authors call the literature limited and of highly variable quality. Its analysis rests on about 300 people, many clinical studies date from the 1950s and 1960s, 15 of its 19 clinical trials were at severe risk of bias, and it counts the 452-person online survey twice, so this page does not use its percentages as rates [10]. A 2026 clinical primer says that controlled trials in patient groups are lacking and that safety in people with cardiovascular, metabolic or psychiatric illness is unclear [11]. A 2026 review of pharmacokinetic studies found mescaline in only two of 32, the two Basel trials, and called it the least studied classic psychedelic in current clinical research [31].

In rats, one study with receptor blockers reports that behavioral changes after mescaline were mediated mainly by the serotonin 2A receptor [17], while a 2026 fMRI study in awake rats gave one strength to two groups of 12 rats and used no blocker, so it does not test that question [18]. Animal findings cannot be carried over to people without testing.

Safety in healthy adults

The safety evidence has a narrow base: participants in the Basel trials were screened for psychiatric and physical illness, tested in a hospital, and watched by staff throughout [1] [2]. In the three-substance trial, mescaline, LSD and psilocybin each raised blood pressure, body temperature and pupil size moderately, which the authors called transient and not a safety concern [1].

Several signals set mescaline apart. All three substances caused more adverse effects than placebo during the first 12 hours, but only mescaline caused significantly more in the 12 to 24 hour window [1]. Severe headache followed mescaline in three participants, and fatigue in two. One participant reported flashback phenomena twice in the weeks after a mescaline session, and no serious adverse event occurred [1]. In the strength-range trial, the text reports vomiting in two of 16 participants at the third strength and in seven at the highest, with ketanserin reducing it to two [2], while a figure legend gives six and one, the pooled safety paper counts six at the highest strength, and the pharmacokinetic paper counts five early vomiters [2] [3] [4], so the count at the highest strength is best read as five to seven. The pooled analysis reported that nausea was the limiting factor and that single administrations in a controlled clinical setting caused no acute psychological or physical harm in healthy participants, which is the authors' conclusion, and they add that 96 administrations are too few to detect rare events and that headache and fatigue were also common after placebo [3]. In the three-substance trial, a depressive episode that lasted days to weeks followed psilocybin in one participant and all three substances in another, and resolved on its own [1]. The pooled analysis mentions one mild depressive episode that lasted about two months after mescaline, and the papers do not say whether this is the same participant [3].

The unscreened world is described less well. The survey article cites a count of 31 single-substance mescaline exposures reported to California Poison Control over 11 years, a secondary report here [5]. Nobody has measured how a cardiovascular, kidney or psychiatric condition changes the picture [11].

Peyote as a species

Peyote raises a question that psilocybin, LSD and DMT do not: whether research should draw on a wild plant that Native American Church organizations and an IUCN assessment both describe as under pressure.

The IUCN Red List classifies L. williamsii as Vulnerable under criterion A4acd, with a decreasing population trend, meaning a suspected population reduction of at least 30 percent. Threats include livestock ranching, plant gathering, illegal collecting, land-use change and commercial harvesting in the United States, and the assessment's wording places part of that pressure on harvesting by religious groups. The decline is an estimate and a projection, and the same assessment describes the species as very abundant across its range. It records a dissenting expert opinion from 2009 that the species should be Least Concern, and the page lists earlier entries of Least Concern (2009) and Vulnerable (2013). The assessment is dated 19 November 2009, was published in 2017, and carries the annotation "needs updating" [16]. Peyote is also on Appendix II of CITES, which requires permits for international trade, with Mexico and the United States as range states [19].

Field data are sparse. A preprint that surveyed six wild populations in Texas found high variation in plant presence and density and could not say which factors drive the differences. The sites were chosen because peyote was known to grow there, and sampling stayed within about 200 metres of a road or trail, so no regional population estimate can be made. The authors could not confirm that peyote is much rarer in West Texas, and their calculation that harvesting 4,000 plants a day would be unlikely to be sustainable rests on an assumed figure, not a measurement [20]. A preprint on a related species, Lophophora diffusa, projected local disappearance within 50 years [21]. Both are unreviewed, and the second concerns a different species. An interview and sales study of the Texas supply side, with just ten church members, argued that scarcity is partly a problem of access, though most informants named scarcity as the main problem [30].

These conservation sources overlap in people. The IUCN assessor is also an author of the Texas population survey [20] and is named in the Native American Church letter as a partner in founding IPCI [22], and three authors of the survey are affiliated with the Cactus Conservation Institute [20]. Agreement among them is not independent confirmation.

Native American Church organizations have made their own case. In an open letter dated 10 May 2021, the National Council of Native American Churches and the Indigenous Peyote Conservation Initiative (IPCI) stated that members noticed smaller and scarcer peyote from the early 2000s, that internal research between 2013 and 2017 confirmed it, and that IPCI was formed in 2017 to support biocultural conservation [22]. They name overharvesting, cattle ranching, mining, energy development and the removal of Indigenous people from the land as causes, an account that differs in emphasis from the IUCN wording above, and ask that decisions about the plant be led by them [22]. This is advocacy by the communities concerned, so its statements of fact are treated as grade 3 and its requests as a statement of what they want.

Later IPCI statements add detail. A March 2023 position statement opposes decriminalization of peyote and pledges to oppose any corporate effort to use peyote to make mescaline [33]. An August 2025 statement opposes legalization or decriminalization of peyote except use under the 1994 amendments to the American Indian Religious Freedom Act, says any extraction of mescaline from natural peyote should be prevented, and says that Indigenous views may not align with synthetic mescaline and that IPCI knows of no policy that prevents it [34]. The group's FAQ says its board has no political position on synthetic mescaline [35]. These statements concern peyote as a plant, not mescaline as a molecule, and they do not speak for all Indigenous people. IPCI and the National Council are United States organizations, and the Wixárika people of Mexico have their own views.

Metanoia's published position is that it will not promote peyote, that it keeps its attention on cultivable, non-threatened sources, and that credit and reciprocity are owed to the communities whose sacrament this is. That a cultivated cactus is a lower-pressure source for research is an untested assumption, and no primary study that tests it was found for this page.

Legal status by jurisdiction

Each entry names its jurisdiction and the source it rests on, and was checked on 2 October 2026 unless it gives another date or says not verified. Some entries rest on third-party reproductions of the legal text. This is not legal advice and grants no permission.

United States, federal. Mescaline is listed in Schedule I in 21 CFR 1308.11(d) for any preparation containing it. Peyote has its own entry, defined as all parts of Lophophora williamsii, whether growing or not, its seeds, extracts, and every compound or preparation of the plant. Mescaline carries DEA code 7381 and peyote 7415. A keyword search of that section for San Pedro, Echinopsis, Trichocereus and cactus found no mention [23]. The eCFR was up to date as of 1 October 2026 (accessed 4 October 2026), and the section was amended in September 2026, which was not examined for any change to these entries. State law other than Colorado's and the Texas provisions below was not examined and is not verified.

Two federal instruments carve out religious use. The regulation at 21 CFR 1307.31 exempts the nondrug use of peyote in bona fide religious ceremonies of the Native American Church from the Schedule I listing, and requires anyone who manufactures or distributes peyote for the church to register every year [24]. The statute, 42 USC 1996a (read in the official 2024 edition of the US Code), part of the 1994 amendments to the American Indian Religious Freedom Act, uses different wording. It makes lawful "the use, possession, or transportation of peyote by an Indian for bona fide traditional ceremonial purposes in connection with the practice of a traditional Indian religion," and defines "Indian" as a member of an Indian tribe [25]. The statute says that this use shall not be prohibited by the United States or any State, and permits reasonable Drug Enforcement Administration regulation of those who cultivate, harvest or distribute peyote [25]. How these instruments apply to any particular person is a legal question that this page does not try to answer.

Texas. Section 481.111(a) of the Texas Health and Safety Code says that its provisions on the possession and distribution of peyote do not apply to the use of peyote by a member of the Native American Church in bona fide religious ceremonies of the church, or to a person who supplies the substance to the church, and the exemption does not apply to a member with less than 25 percent Indian blood. Texas places peyote in Penalty Group 3 unless it is unharvested and growing in its natural state, and mescaline in Penalty Group 2 [25] [36]. How the Texas clause and the federal statute interact was not examined here.

Colorado. The state's Natural Medicine Health Act defines "natural medicine" as psilocybin and psilocyn. It lets the state add mescaline, among other substances, if its advisory board recommends and state officials approve, on or after 1 June 2026, and the same section says that "mescaline" does not include peyote [26]. The statute was read on a third-party reproduction of the Colorado code, so this entry is not verified against the official publication, and whether any addition has taken place was not verified. A separate question is open: the 2022 ballot text of Proposition 122, read in part, defined natural medicine for the personal-use provisions with a longer list that includes mescaline other than peyote, and IPCI's 2025 statement says that other mescaline-containing cacti were included in Colorado's law [26] [34]. Whether the personal-use provisions cover mescaline that does not come from peyote today was not verified and is not stated here as fact.

International. Mescaline appears in Schedule I of the 1971 UN Convention on Psychotropic Substances in the UNODC text of the treaty, and no entry for the peyote plant itself was found in that schedule. Article 32 lets a state with wild plants containing Schedule I substances, traditionally used by small, clearly determined groups in magical or religious rites, enter a reservation for those plants in respect of article 7, except for its provisions on international trade [27]. The Basel trial report states approval by the Swiss Federal Office for Public Health [1], a research route under at least one national system, though Swiss law itself was not examined. The IUCN assessment states that collecting peyote is illegal in Mexico [16], which is its account, not a reading of Mexican law from a primary source. The UNODC file may not reflect later changes to the schedules, and other countries were not examined.

History and tradition

No ethnographic study (grade 4) was read for this page. The facts below are archaeological, legal and institutional, and the section is told from outside the communities concerned.

The oldest physical evidence comes from rock shelters in the Lower Pecos region of Texas, and the details of its dating are contested. A 2005 study radiocarbon dated two peyote specimens held at the Witte Museum in San Antonio, presumably from Shumla Cave No. 5, to a calibrated one-sigma interval of 3780 to 3660 BC, found mescaline in both, and concluded that native North Americans recognized peyote's psychoactive properties as long as 5,700 years ago [12]. A later study of three samples from Shumla caves reported ages that calibrate to 4045 to 3960 BC at two sigma, described the samples as aggregates of ground peyote mixed with other plant material, not intact buttons, and noted that this age is about 250 radiocarbon years older than one reported earlier [29]. The sources read do not establish whether the Witte specimens are of the same kind, and the conclusion about what people understood remains an inference from the chemistry.

For the Native American Church, the best-documented statements come from the church's own organizations and from federal law, which describes ceremonial peyote use as integral to a way of life [25]. This page does not describe ceremony, because writing about it from journal articles would repeat a distortion that Indigenous representatives have warned about [22].

The same restraint applies to the Wixárika (Huichol) people of Mexico. On 12 July 2025 UNESCO inscribed the Wixárika Route through Sacred Sites to Wirikuta on the World Heritage List [28]. The advisory evaluation of the nomination, read for every passage that mentions peyote, relays the Mexican state's account that the Wixárika regard peyote as a repository of knowledge and records that tourist demand has led to unsustainable use of the plant, affected biodiversity and reduced the availability of peyote for traditional rituals, along with mining concessions and legal protection by a regional Wixárika council since 2011, which led to a pause in mining [32]. How the pilgrimage relates to the plant is for Wixárika people and for ethnography to say.

What is not known, and what Metanoia asks

Lasting change

The controlled trials followed participants for about a day, with flashbacks tracked for weeks [1] [2]. No controlled study has measured mescaline's effect on how healthy adults think, feel or relate to others a month, six months or a year later, and the surveys cannot fill this gap. The registry entry for the strength-range trial lists secondary outcomes that its 2024 paper does not report, among them blood BDNF, cytokines, oxytocin, an empathy test, well-being and life-satisfaction questionnaires and a heart-rhythm measure, and it showed no posted results when read on 2 October 2026 [37]. The entry for the three-substance trial likewise lists brain-imaging connectivity among its main outcomes with no posted results [38]. Whether these data, which touch empathy and well-being, will be reported is not known. For Metanoia, this is the central empty space.

Purified compound versus plant

Every controlled human study used pharmaceutical-grade mescaline hydrochloride [1], and none has compared it with cactus material. In the survey, ratings of the acute effects did not differ by source, but the peyote group reported taking it more times and having shorter sessions, and a cross-sectional survey cannot tell why [5]. Whether the plant differs from the purified compound in any way that matters is open.

Variation in the plant

With roughly ninety-fold variation in San Pedro concentration [13] and peyote plants that lack mescaline [15], a study of plant material that does not measure what was in it cannot be interpreted.

Who has been studied

The Basel participants were young to middle-aged, screened and mostly experienced, and the survey respondents were mostly white, male and North American. Indigenous communities are almost absent from both [5]. Nothing in this literature speaks for the people who have used the plant longest.

Whether the research can be done without harming the plant

Peyote's last full assessment dates from 2009 [16], and the field data are thin: a Texas preprint whose sample is not representative [20], a preprint on a related species [21], and a study of the Texas market [30]. Treating peyote as study material would work against Metanoia's own commitment to sustainability.

Metanoia's questions for mescaline follow from these gaps. What does a standardized, chemically characterized preparation of a cultivable source do in healthy adults over months rather than hours? How does it compare with psilocybin and LSD on the twelve dimensions Metanoia measures, given that the acute experience looks so similar? What does the variation among cacti mean for any study that uses them? And how can this be asked without drawing on a species that its own traditional keepers say is under pressure? Metanoia records what the material was, what exposure occurred, the context, and the outcome, and it is developing an outcome measure for the twelve dimensions. That infrastructure is not yet built for this substance. This page describes questions and does not announce a study.

The book on all twelve dimensions   Back to the twelve dimensions