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Types of psychedelics: a plain guide to the main groups

BySafe Ceremonies

“Psychedelic” gets used loosely. Retreat websites put ayahuasca, ketamine, MDMA, Kambo and cacao on the same menu, as if they were variations on one thing. They aren’t. They act on different parts of the brain and body, last from minutes to days, interact with different medicines and carry different risks.

This guide sorts the substances you’re likely to see offered into plain groups, based on how they work. It’s an overview, not a ranking, and it doesn’t cover doses or sourcing. Knowing which group something belongs to is a good first step in asking the right safety questions.

Classic psychedelics

Scientists use “classic psychedelic” for substances that act mainly by switching on one type of serotonin receptor in the brain, the 5-HT2A receptor. A review in Pharmacological Reviews by the pharmacologist David Nichols groups them into three chemical families:

  • Tryptamines: psilocybin (in “magic mushrooms”), DMT (in ayahuasca) and 5-MeO-DMT (in the secretion used in bufo ceremonies).
  • Ergolines: LSD.
  • Phenethylamines: mescaline, from the peyote and San Pedro cacti.

They have a lot in common. They change perception, emotion and the sense of self. According to the US National Institute on Drug Abuse (NIDA), they don’t typically lead to addiction. Taking one repeatedly over a few days quickly builds tolerance, and tolerance to one carries over to the others. Their main dangers are psychological and behavioral: overwhelming fear, risky behavior while affected and, in people who are vulnerable, longer-lasting problems such as psychosis.

Where they differ most is in how long they last:

  • Inhaled 5-MeO-DMT: effects peak within minutes and are largely gone in about half an hour.
  • Inhaled DMT: under 30 minutes.
  • Ayahuasca: around four hours per cup.
  • Psilocybin: about five hours on average in a lab study.
  • LSD: about eight hours in the same study.
  • Mescaline: about eleven hours, the longest of the three compared.

Ayahuasca is a special case within this group. Its vine contains compounds that block an enzyme called MAO-A, which is what lets the DMT work when swallowed. That same action is why ayahuasca carries serious interaction risks with SSRI antidepressants and other serotonin-raising drugs. Our ayahuasca guide explains this.

Dissociatives

Dissociatives work mainly by blocking a different brain chemical, glutamate, at what are called NMDA receptors. NIDA lists ketamine and PCP as examples and describes them as making people feel disconnected from their body and surroundings.

Ketamine is the one you’re most likely to see in a wellness setting. It is used in medicine as an anesthetic, and a closely related drug, esketamine, was approved by the US Food and Drug Administration in 2019 as a nasal spray for treatment-resistant depression. NIDA notes that ketamine use can lead to withdrawal symptoms, unlike the classic psychedelics, and that ketamine and PCP can worsen symptoms in people with schizophrenia.

Ketamine offered by a medical clinic, under a prescriber, is a different proposition from ketamine offered at a retreat. Our guide to ketamine and MDMA offerings goes into what to ask.

MDMA

MDMA is often grouped with psychedelics, but the Nichols review places it in a separate class called entactogens or empathogens, because it acts differently and is known for producing feelings of closeness and emotional openness rather than visions.

MDMA-assisted therapy for PTSD has been studied in clinical trials. In August 2024 the FDA declined to approve it, citing significant limitations in the data, and asked for a further phase 3 trial.

Atypical psychedelics

Some substances produce strong altered states without fitting the classic pattern.

  • Ibogaine, from the iboga shrub of Central Africa, works differently from the classic psychedelics, and its main metabolite stays in the blood for days. Its biggest risk is to the heart, through a disturbance of heart rhythm. Our iboga guide covers this in detail.
  • Salvinorin A, the active compound in Salvia divinorum, acts on kappa opioid receptors rather than serotonin receptors. The Nichols review lists it as outside the classic group for that reason.

Ceremony practices that aren’t psychedelic

Several things listed next to plant medicines don’t produce psychedelic effects at all, and it helps to know which.

  • Kambo is the skin secretion of an Amazonian frog. It contains peptides that cause rapid vomiting, sweating, swelling and swings in heart rate and blood pressure, and no visions. Its serious risks include dangerously low sodium and heart problems.
  • Cacao ceremonies use a drink made from the cacao bean, the source of chocolate. Cacao isn’t a psychedelic. A cacao ceremony is built around the setting, the music and the people, and our cacao guide explains what to expect.
  • Breathwork, sound baths and meditation involve no substance. They can still bring up strong emotions, and our breathwork guide covers the safety questions specific to it.

“Plant medicine” or “drug”?

Ceremony centers often draw a line between plant medicines and lab-made drugs. Chemically, the line is blurry. The psilocybin in a mushroom and the synthetic psilocybin used in clinical trials are the same molecule. Mescaline can come from a cactus or a lab. DMT is the same compound whether it’s in a brew or a vial.

What does differ is what else comes with it. A plant contains a varying amount of the active compound, along with other compounds that may change its effects, and nobody can tell you the strength of a given batch without testing it. A pharmaceutical product has a known amount and a known purity, and it’s given under medical rules. The US National Center for Complementary and Integrative Health has a page on exactly this point: natural doesn’t necessarily mean safer or better, and everything, natural or not, is made of chemicals.

Neither setting is automatically safe. The questions that matter are the same in both: what exactly am I being given, who screened me, and who is there if something goes wrong?

Why the categories matter for your safety

Knowing the group helps you ask better questions.

  • Interactions differ. MAO-blocking brews like ayahuasca carry interaction risks that psilocybin alone doesn’t. Ibogaine’s effect on heart rhythm makes any other medicine that affects heart rhythm a concern. Kambo combined with heavy water drinking can drive sodium dangerously low.
  • Durations differ. A twelve-hour mescaline night needs different staffing from a fifteen-minute session.
  • Combinations multiply risk. A retreat that offers several substances in one week needs to screen for each one, and to say how it spaces them.
  • Evidence differs. Some substances have been through large clinical trials; others have almost none. “Psychedelics are being studied for depression” says little about the substance you’re being offered.
  • Legal status differs by substance and by country. Our legal guides go into this, and laws change.

A drug-interaction review published in 2024 found that combining classic psychedelics with other drugs could weaken, strengthen or leave their effects unchanged depending on the combination. Bring a full list of your medicines to any screening, and never stop a prescribed medicine on a center’s advice. Talk to the person who prescribed it.

More guides

Safe Ceremonies covers all of these practices, from plant medicine to clinics. You can search the listings and read reviews by category, such as psilocybin and mushrooms, psychedelic-assisted therapy and Kambo.

Sources

Photo: Reading room in Ipswich library by JuliaC2006, CC BY 2.0.

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