San Pedro

Plant Medicine

San Pedro (Echinopsis pachanoi, also called wachuma) is a fast-growing Andean columnar cactus that contains mescaline. Used in Andean healing traditions for thousands of years, it produces a long, gentle psychedelic experience and is a far more sustainable mescaline source than peyote.

Also known as: Echinopsis pachanoi, Trichocereus pachanoi, Wachuma, Huachuma, Aguacolla, Mescaline cactus

Written by Psymerge Editorial Team · Last updated June 4, 2026

Key facts

CategoryPlant Medicine
Onset1–2 hours
Peak3–5 hours
Total duration10–12 hours (sometimes longer)
After-effectsTiredness and a gentle afterglow into the next day

Overview

San Pedro — known in the Andes as wachuma — is a tall, fast-growing columnar cactus native to the Andean regions of Peru, Ecuador, and Bolivia. Like peyote, its psychedelic effects come from mescaline, a phenethylamine that acts mainly as an agonist at serotonin 5-HT2A receptors (Cassels & Sáez-Briones, 2018), though San Pedro generally contains a lower concentration than peyote. It is traditionally prepared by boiling slices of the cactus into a brew.

The experience is long, typically 10–12 hours or more, and is often described as gentle, warm, and nature-connected, usually preceded by nausea. San Pedro has been used in Andean healing ceremonies for thousands of years and continues in living curandero traditions today.

Because it grows quickly and is widely cultivated, San Pedro is a much more sustainable source of mescaline than the slow-growing, endangered peyote. This page summarises its effects and risks; for the underlying pharmacology, see also our page on mescaline.

History & origins

San Pedro has an ancient ceremonial history in the Andes. Carved depictions and ritual remains associated with the cactus appear at sites linked to the Chavín culture of Peru, and its ceremonial use is generally held to stretch back two to three thousand years, with some archaeological evidence suggesting considerably older use. The name 'San Pedro' (Saint Peter) reflects the syncretism that followed Spanish colonisation, blending Indigenous practice with Catholic imagery.

Its active alkaloid, mescaline, was first isolated from peyote in the late nineteenth century and characterised in the twentieth (Cassels & Sáez-Briones, 2018). San Pedro remains central to Andean curandero (healing) traditions and has spread internationally as interest in plant medicines has grown.

Pharmacology & how it works

San Pedro's psychedelic effects come from mescaline, a phenethylamine that acts mainly as an agonist at 5-HT2A serotonin receptors and also binds 5-HT1A and α2A receptors (Cassels & Sáez-Briones, 2018). San Pedro generally contains a lower concentration of mescaline than peyote, alongside minor alkaloids.

Chemical class
Mescaline-containing cactus (phenethylamine psychedelic)
Routes of administration
Oral (boiled brew or tea from cactus slices), Oral (dried and powdered cactus)
Tolerance
Tolerance builds with repeated use and is cross-tolerant with other 5-HT2A psychedelics, but it resets after a few days; there is no physical dependence.

Pharmacokinetics

Taken orally as a brew, San Pedro tends to come on a little more slowly than peyote — often over 1–2 hours — peaks at 3–5 hours, and lasts around 10–12 hours or more. Its active compound, mescaline, is largely excreted unchanged in the urine.

Effects

Physical Effects

  • Nausea and vomiting, especially as the brew is consumed
  • Increased heart rate and blood pressure
  • Pupil dilation
  • Sweating and changes in body temperature
  • Loss of appetite
  • Tremor or restlessness

Psychological Effects

  • Rich, colourful visual patterns and enhanced colour perception
  • A warm, gentle, emotionally open mood
  • Deep introspection and shifting trains of thought
  • A strong sense of connection to nature and surroundings
  • A distorted sense of time
  • Anxiety or difficult emotions during challenging experiences

Spiritual Effects

  • Mystical or unitive experiences
  • Feelings of reverence, gratitude, and connection
  • A sense of communion with nature or the sacred, central to Andean ceremonial use

Dosage Information

Low: 15–25 cm of fresh cactus column (oral, ~6–8 cm diameter)
Medium: 25–50 cm of fresh cactus column (oral, ~6–8 cm diameter)
High: 50+ cm of fresh cactus column (oral, ~6–8 cm diameter)

San Pedro is much lower in mescaline than peyote (roughly 0.3–2% of dry weight) and is usually prepared as a boiled brew from slices of the column. Potency varies greatly between specimens, so dosing by length is only a rough guide and is best based on mescaline content where known. A typical psychoactive amount delivers on the order of 200–400 mg of mescaline. Educational only and not an endorsement of use.

Risks & safety

Contraindications

San Pedro raises heart rate and blood pressure and produces a very long altered state, so it is generally inadvisable for:

  • Cardiovascular conditions: heart disease, uncontrolled high blood pressure, or a history of stroke.
  • Psychiatric history: a personal or family history of psychosis, schizophrenia, or bipolar disorder.
  • Use of serotonergic medications or lithium (see interactions below).
  • Pregnancy and breastfeeding.

Drug interactions

Because its active compound is mescaline, San Pedro carries the same interaction risks as mescaline.

  • Lithium: combining lithium with classic psychedelics has been associated with seizures and is considered particularly dangerous.
  • MAOIs: can intensify and prolong effects and raise the risk of serotonin toxicity. (Note that some people combine San Pedro with MAOI-containing plants, which increases this risk.)
  • SSRIs, SNRIs, and other serotonergic drugs: raise the risk of serotonin syndrome.
  • Stimulants: add cardiovascular strain.

This list is not exhaustive. Disclose all medications to a clinician before considering use.

Psychological distress & bad trips

San Pedro's very long duration means a difficult experience can be especially tiring and hard to wait out. Challenging episodes may involve anxiety, fear, or distressing emotional material, and early nausea can add to discomfort. A calm, supportive setting — traditionally, an experienced curandero — substantially reduces the risk of a difficult experience becoming harmful.

Rare but serious risks

San Pedro (through mescaline) has a relatively wide safety margin and low physical toxicity, but risks are not zero:

  • Cardiovascular strain: raised heart rate and blood pressure can be dangerous for people with heart conditions.
  • A very long, demanding experience: 10–12 hours or more can be exhausting, and vomiting can lead to dehydration.
  • Accidents and impaired judgment over a long period increase the risk of injury.
  • Misidentification: some ornamental cacti resemble San Pedro but contain little mescaline or other compounds, so plant identity matters.
  • Dangerous drug interactions, especially with lithium (seizure risk) and serotonergic medications.

Vulnerable populations

Some groups face higher risk and should avoid San Pedro:

  • People with a personal or family history of psychosis, schizophrenia, or bipolar disorder.
  • People with heart disease or uncontrolled high blood pressure.
  • People taking lithium, MAOIs, antidepressants, or other serotonergic medications.
  • Adolescents, whose brains are still developing.
  • Pregnant or breastfeeding people.

Dependency & addiction potential

Like other classic psychedelics, San Pedro is not considered addictive. It does not produce physical dependence or compulsive use, and tolerance fades after a few days. Research on long-term ceremonial use of the closely related peyote found no evidence of lasting psychological or cognitive deficits (Halpern et al., 2005).

Overdose

Mescaline, San Pedro's active compound, has a wide safety margin, and there is no well-established lethal dose in humans; serious toxicity and death are very rare and usually involve other drugs or pre-existing medical conditions. The main acute dangers are cardiovascular strain, dehydration from vomiting, and accidents during the long experience. If someone develops chest pain, a dangerously high heart rate, seizures, a very high temperature with muscle rigidity (possible serotonin syndrome), or loss of consciousness, seek emergency medical help immediately.

Harm Reduction

  • Start low and wait: onset is slow (often 1–2 hours) and potency varies between plants, so do not redose early.
  • Confirm the plant's identity: some ornamental columnar cacti look similar but differ greatly in mescaline content.
  • Set aside a full day and a safe, comfortable environment, since effects last 10–12 hours or more.
  • Have a sober, trusted sitter or experienced curandero present, and never use alone.
  • Avoid combining with lithium, MAOIs, SSRIs, or other serotonergic medications — the lithium combination in particular has been linked to seizures.
  • Expect nausea: eat lightly beforehand and stay hydrated throughout.
  • Avoid San Pedro if you have a heart condition or a personal or family history of psychosis.

Cultural & spiritual context

San Pedro, or wachuma, is woven into Andean healing traditions, where it is used by curanderos in night-time ceremonies (mesadas) for healing, divination, and spiritual guidance. These are living practices with their own protocols, songs, and ritual objects, and the cactus is regarded as a teacher and ally rather than a recreational drug.

Compared with peyote, San Pedro raises fewer conservation concerns: it grows quickly, is widely and easily cultivated, and is not endangered. For this reason it is often recommended as a more sustainable and ethical source of mescaline. As with all Indigenous plant traditions, engaging respectfully — and being cautious of unregulated commercial 'retreats' — matters a great deal.

Legal Status

Laws vary widely by country and change frequently, so we don't track legal status here to avoid showing outdated information.

Check current worldwide legal status on Psychedelic Alpha

Frequently asked questions

How long does a San Pedro experience last?

San Pedro is long-acting. Prepared as a brew it tends to come on over 1–2 hours, peaks at around 3–5 hours, and lasts roughly 10–12 hours or more, with tiredness and a gentle afterglow often continuing into the next day.

How is San Pedro different from peyote?

Both are mescaline-containing cacti with similar effects, but San Pedro is a fast-growing Andean columnar cactus that is lower in mescaline and widely cultivated, whereas peyote is a small, slow-growing North American cactus that is far more concentrated but endangered. San Pedro is generally the more sustainable source.

Is San Pedro addictive?

No. Like other classic psychedelics, San Pedro does not cause physical dependence or compulsive use, and tolerance fades after a few days. Research on the closely related peyote found no lasting cognitive deficits from long-term ceremonial use (Halpern et al., 2005).

Why does San Pedro cause nausea?

Nausea and vomiting are common when drinking the bitter brew, which contains mescaline alongside other alkaloids. In Andean traditions this purging is often regarded as a cleansing and meaningful part of the ceremony.

Is it dangerous to combine San Pedro with antidepressants or lithium?

It can be. Combining classic psychedelics with lithium has been linked to seizures, and MAOIs, SSRIs, and other serotonergic drugs can raise the risk of serotonin toxicity. Any decision about stopping prescribed medication should be made only with a clinician.

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References & further reading

  • Cassels, B. K., & Sáez-Briones, P. (2018). Dark Classics in Chemical Neuroscience: Mescaline. ACS Chemical Neuroscience, 9(10), 2448–2458. https://doi.org/10.1021/acschemneuro.8b00215
  • Halpern, J. H., Sherwood, A. R., Hudson, J. I., Yurgelun-Todd, D., & Pope, H. G., Jr. (2005). Psychological and Cognitive Effects of Long-Term Peyote Use Among Native Americans. Biological Psychiatry, 58(8), 624–631. https://doi.org/10.1016/j.biopsych.2005.06.038
  • Nichols, D. E. (2016). Psychedelics. Pharmacological Reviews, 68(2), 264–355. https://doi.org/10.1124/pr.115.011478
  • National Institute on Drug Abuse (NIDA). Psychedelic and Dissociative Drugs. https://nida.nih.gov/research-topics/psychedelic-dissociative-drugs
  • European Monitoring Centre for Drugs and Drug Addiction (EMCDDA). Drug profiles. https://www.emcdda.europa.eu/publications/drug-profiles_en
  • Erowid. San Pedro / Cacti Vault. https://www.erowid.org/plants/cacti/
  • DanceSafe. https://dancesafe.org/drug-information/
  • TripSit. Drug combinations chart. https://wiki.tripsit.me/wiki/Drug_combinations

About this article

Written by:
PE
Psymerge Editorial Team
Last updated June 4, 2026