What is psilocybin?

Psilocybin is the main psychoactive compound in psilocybin mushrooms, a group of fungi from at least eight genera, most of them in the genus Psilocybe.^1,18 Chemically it's a tryptamine, a close relative of the brain chemical serotonin. It was first isolated in 1958, by Albert Hofmann's team at Sandoz,²² and today it's both a Schedule I drug and the subject of late-stage clinical trials for depression.

How psilocybin works

Psilocybin itself does very little. In the body, enzymes strip off a phosphate group and turn it into psilocin, the compound that produces the effects.² That's why researchers call psilocybin a prodrug.

Psilocin activates serotonin 5-HT2A receptors. The first human evidence for this came in 1998, when ketanserin, a drug that blocks those receptors, prevented psilocybin's psychological effects in healthy volunteers.³ A 2019 brain-imaging study found that how intense people rated their experience tracked how many 5-HT2A receptors psilocin was occupying and how much psilocin was in their blood.⁴

How long it takes and how long it lasts

Drug agencies describe effects starting within about 30 minutes to two hours after mushrooms are eaten, and lasting about four to six hours.^5,6,8 Poison centers note that effects can occasionally last up to 12 hours.⁸

Controlled studies give a closer look. In healthy volunteers given psilocybin by mouth, psilocin in the blood peaked about two hours later, and subjective effects lasted on average about five and a half to six and a half hours, depending on the dose group.⁷ The body clears psilocin fairly quickly, with a half-life of under two hours.⁷

What it does

Psilocybin changes perception, mood and thinking. Commonly described effects include visual distortions and hallucinations, a changed sense of time, and strong emotions that can swing from euphoric to frightening.^5,6 Physical effects can include nausea and a faster heart rate.⁹

The most likely serious risk is overwhelming distress during the experience, which can lead to dangerous behavior, especially for people who are unprepared or alone.¹⁴ Our safety guide covers who should avoid psilocybin and which medicines interact with it.

Tolerance

Tolerance builds quickly. With repeated use over a short period, psilocybin has less and less effect, and according to Australia's Alcohol and Drug Foundation, sensitivity returns after about a week without use.⁵ Psilocybin and LSD also show cross-tolerance: studies in the early 1960s found that tolerance to one blunted the effects of the other.¹⁰

Toxicity and addiction potential

By the standards of psychoactive drugs, psilocybin's direct physical toxicity is low. A comparison of 20 substances found that several hallucinogens, psilocybin among them, had the least direct physiological toxicity, and most published reports of fatal poisoning involved another substance as well, most often alcohol.¹³

Its addiction potential also appears low. A 2018 review organized around the eight factors the government uses to schedule drugs found that psilocybin has limited reinforcing effects in animals, and that the harms associated with its use are low compared with typical drugs of abuse. The authors suggested Schedule IV would fit an approved psilocybin medicine.¹¹ Regular use doesn't appear to cause physical dependence.⁵

Low risk isn't no risk. In the Global Drug Survey, 19 of 9,233 people who had used magic mushrooms in the past year, about 0.2%, had sought emergency treatment, mostly for anxiety, panic or paranoia. The reasons they gave were most often a poor mindset, a poor setting or mixing substances. All but one were back to normal within 24 hours.¹² People with a personal or family history of psychotic disorders face a higher risk of lasting harm.^11,14

Psilocin's relatives

Mushrooms also contain smaller amounts of related compounds: baeocystin, norbaeocystin and aeruginascin. Their effects in people haven't been fully established.¹⁵ In mice, psilocybin and psilocin produced the head-twitch response researchers use as a sign of psychedelic activity, while baeocystin and aeruginascin did not.¹⁶ Whether these minor compounds change the overall experience, an idea sometimes called the entourage effect, is still an open question.

Why potency varies

The amount of psilocybin in a mushroom varies a lot. A study of 226 mushrooms from 82 collections described tryptamine levels as extremely variable.¹⁵ When researchers grew 14 strains of Psilocybe cubensis under identical conditions, total tryptamines differed more than 7.8-fold between strains, and individual mushrooms of the same strain differed too.¹⁷ That's why a strain name or species can't tell you the strength of a particular batch. Our guides to cubensis strains and reading a lab report go into more detail.

Where psilocybin is found

Psilocybin occurs in species from at least eight genera: Psilocybe, Panaeolus, Gymnopilus, Inocybe, Conocybe, Galerina, Pholiotina and Pluteus.¹⁸ Most cultivated psilocybin mushrooms are believed to be Psilocybe cubensis.¹⁸ Several of these genera also contain deadly poisonous species, which is why wild mushrooms should never be eaten without an expert's identification. See our species guide.

Legal status

Psilocybin and psilocin are Schedule I controlled substances under U.S. federal law, the category for drugs with no accepted medical use.¹⁹ Oregon and Colorado license supervised adult use, New Mexico is building a medical program, and dozens of cities have made enforcement a low priority, but none of that changes federal law. Our state-by-state map has the details.

The research

No psilocybin medicine is FDA-approved yet. Compass Pathways expects to complete the first application, for a synthetic psilocybin to treat treatment-resistant depression, in the fourth quarter of 2026.²⁰ Our research tracker follows that and the other trials.

Use is already widespread: a 2026 analysis of federal survey data estimated that about 8 million Americans aged 12 and older used psilocybin in the past year.²¹ More on that in our news report.

Common questions

Is psilocybin addictive?

Research suggests its addiction potential is low. It produces little drive to keep taking it in animal studies, doesn't appear to cause physical dependence, and tolerance builds so fast that repeated use soon has little effect.^5,11

How long does psilocybin last?

Effects usually start within about 30 minutes to two hours after eating mushrooms and last about four to six hours, occasionally up to 12.^5,6,8

Can you overdose on psilocybin?

Its direct physical toxicity is low, and most reported deaths involved another substance, often alcohol.¹³ The more common dangers are severe distress, risky behavior while intoxicated, mistaking a poisonous mushroom for a psilocybin mushroom, and drug interactions.¹⁴ If someone is in danger, call 911. For a possible poisoning, call Poison Control at 1-800-222-1222.

Is psilocybin legal in the United States?

Not under federal law.¹⁹ A few states have created regulated programs or medical pilots, and some cities have deprioritized enforcement. See the legal status map.