Classic Psychedelics: What the Term Covers

What the term covers

"Classic psychedelics" is a pharmacology term, not a cultural one. The US Food and Drug Administration (FDA) describes classic psychedelics as typically understood to be 5-HT2A receptor agonists, such as psilocybin and lysergic acid diethylamide (LSD). [1] The US National Institute on Drug Abuse (NIDA) uses the same idea: its psychedelic group is made of drugs that primarily influence how the brain processes serotonin, and it names psilocybin, LSD, DMT and mescaline. [2] A 2016 pharmacology review reports a consensus that these drugs are agonists or partial agonists at brain serotonin 2A receptors. [3]

An "agonist" is a substance that switches a receptor on. A receptor is a docking point on a brain cell. The page Serotonin Receptors in Plain Language explains what this does and does not tell us.

The four named examples

Each example has a different origin, which is one reason the word "classic" should not be read as "natural" or "traditional".

Each has its own guide: psilocybin, LSD, DMT and mescaline. DMT and ayahuasca are not the same thing: see DMT vs Ayahuasca.

What they are reported to do

NIDA reports that people using these drugs describe vivid visions or sensations, a changed sense of self, and feelings ranging from intense happiness and connection to fear, anxiety and confusion. [2] NIDA says studies suggest the most prominent effects stem from activity in the prefrontal cortex and that these drugs temporarily disrupt communication between brain regions, including the default mode network. [2] How much that matters for any health benefit is a separate question, covered in Proposed Mechanisms vs Proven Clinical Outcomes.

What "classic" does not mean

• Not "safe". NIDA says effects vary widely and can include fear, anxiety and dangerous behavior, and that there is some evidence these drugs might trigger a schizophrenia-like illness in people with predisposing factors. [2]
• Not "natural". LSD is semisynthetic. [5]
• Not "the same drug". The four examples differ in origin, chemistry and the research behind them. See Why Different Substances Cannot Be Treated as Equivalent.
• Not "approved medicine". NIDA's page on medicines states that only esketamine is FDA approved for therapeutic use to date, and that FDA has granted Breakthrough Therapy designation to two psilocybin formulations being studied for depression. [8] A designation speeds up research review. It is not an approval.
• Not everything that is psychoactive. MDMA, ketamine, ibogaine and salvia are placed in other groups by NIDA. [2]

Evidence labels on this page

This page makes classification statements, not treatment claims. Where it touches approval it uses the label approved medicine (a regulator has approved a product for a stated use) only for what the regulator has actually approved. Treatment evidence for specific conditions is on the pages for major depressive disorder and PTSD. The full list of labels is in how we label evidence.

Safety note

Fear and anxiety are among the most common difficult effects, and fatal overdoses are described by NIDA as rarely associated with typical use of the commonly used members of this group. [2] NIDA also says that illicitly made drugs can be contaminated with other dangerous substances. [2] For the full risk picture see Psychedelic Adverse Effects and Contraindications. In the US, 911 is the emergency number and 988 reaches the Suicide and Crisis Lifeline.

Education only

This guide describes categories. It gives no amounts, no sourcing or preparation information and no advice to use or to treat yourself.