Why do magic mushrooms cause nausea, yawning and dilated pupils? What studies record

People who have taken magic mushrooms often describe feeling them in the body before anything else: an unsettled stomach, yawning, a chill, a pounding heart. Searches like “do shrooms dilate pupils” and “why do shrooms make you yawn” are common. This guide explains what is known about why these body effects happen, how often controlled studies have recorded each one, and where the science simply has no answer yet.

It also covers the point that matters most for safety: some body symptoms are not a normal effect of psilocybin at all. They can be a sign of a poisonous mushroom, a dangerous drug interaction or a heart problem.

Why do magic mushrooms have body effects at all?

Magic mushrooms contain psilocybin, which the body converts into psilocin, the active form (we explain the difference in psilocin vs psilocybin). Psilocin acts on serotonin receptors, especially the serotonin 2A receptor. A brain-imaging study in eight healthy volunteers found that psilocybin occupied up to 72% of these receptors, and that how intense people rated the experience tracked both receptor occupancy and blood levels of psilocin (Madsen et al., 2019). Evidence: established for the mental effects; that study did not measure body symptoms.

Psychedelics do more than change perception. A 2022 review describes the body effects of psychedelics as “sympathomimetic”, meaning they resemble the body’s fight-or-flight response: rises in heart rate, blood pressure, pupil size and body temperature that it calls short-lived and not clinically significant in the studies it reviewed (Schlag et al., 2022).

The clearest evidence that the 2A receptor drives some body effects comes from LSD, not psilocybin. In a randomized, placebo-controlled crossover study of 24 healthy volunteers, ketanserin, a drug that blocks the 2A receptor, given after LSD reversed LSD-induced pupil dilation, reduced the overall rise in blood pressure and reduced nausea ratings over the session (Becker et al., 2023). That is consistent with the idea, but we found no equivalent study measuring body symptoms after psilocybin. Evidence: preliminary for psilocybin.

Why do shrooms cause nausea and vomiting?

Nausea is one of the most consistently recorded effects. A 2024 systematic review and meta-analysis pooled adverse events from clinical and research studies of classic psychedelics. For psilocybin, nausea was reported by 24.2% of participants (25 study groups, 718 people), vomiting by 4.8% (9 groups, 271 people) and abdominal discomfort by 7.6% (Hinkle et al., 2024). The review pooled effects during the experience with those in the following two days, and its authors say the findings cannot be generalized to unsupervised use outside clinical settings.

Placebo-controlled trials confirm that this is the drug, not just nerves. A 2024 meta-analysis of six randomized, double-blind trials in 528 people treated for depression or anxiety found nausea was about 8.9 times as likely after psilocybin as after a comparison treatment (relative risk 8.85). Headache, anxiety, dizziness and raised blood pressure were also more likely, and the authors report that the acute adverse effects resolved within 48 hours (Yerubandi et al., 2024). Evidence: established that nausea is common in trials.

Why it happens is less settled. Health Canada describes dry mouth, sometimes leading to nausea and vomiting (Health Canada). Serotonin receptor activity is a likely part of it, given the LSD and ketanserin result above, and researchers who analysed mushroom experience reports note that the early nausea and restlessness resemble an acute stress reaction (Brouwer et al., 2025). Whole mushrooms also contain other material besides psilocybin, and no study we found has separated the role of each. Evidence: unresolved.

Timing matters for understanding the experience. In a qualitative study of 2,343 psilocybin mushroom reports on Erowid, the researchers coded 47 descriptions of the “come-up” and found nausea in 34% of them, the most common theme. The come-down was more often described in positive terms (Brouwer et al., 2025). These are self-selected online accounts, and the authors say their method cannot show what percentage of all users feel nausea.

Do shrooms dilate pupils?

Yes. Dilated pupils (mydriasis) are among the physical signs listed in safety guidelines for human hallucinogen research (Johnson et al., 2008), and they have been measured. In a randomized, double-blind, placebo-controlled crossover study of 32 healthy participants, psilocybin, LSD and mescaline each increased pupil size compared with placebo, with no difference between the three. The authors describe the autonomic effects as moderate, transient and not a safety concern in that setting (Ley et al., 2023).

Wider pupils are part of the fight-or-flight-like pattern described above (Schlag et al., 2022). In the LSD study, blocking the 2A receptor reversed the pupil dilation (Becker et al., 2023). The 2024 review did not have enough psilocybin studies reporting mydriasis to pool them; for LSD it estimated 72.6% (Hinkle et al., 2024). A review of mushroom poisonings also lists mydriasis among reported signs after hallucinogenic mushrooms (Graeme, 2014).

Evidence: established that psilocybin enlarges pupils; how much it varies between people is not well described.

Why do shrooms make you yawn?

Honestly, nobody has studied this properly. Yawning shows up in the data: the 2024 review estimated it in 11.4% of psilocybin participants, but only three study groups (94 people) reported it, and the confidence interval runs from 3.3% to 32.6% (Hinkle et al., 2024). Yawning, feeling cold and sweating are also mentioned in mushroom experience reports describing the come-up (Brouwer et al., 2025). We found no study designed to explain yawning after psilocybin.

What is known is general. A 2025 review of yawning says it is started mainly by the hypothalamus and brainstem, with dopamine, serotonin and oxytocin playing roles, and that agonists of serotonin 2 receptors induced yawning in several studies (Wani and Agarwal, 2025). Other serotonin drugs cause yawning too: in a prospective study of 110 patients starting an SSRI antidepressant, excessive yawning rose from 5.4% to 15.4% after a month (Yıldırım et al., 2026).

Putting those together, it is plausible that psilocin’s action on serotonin receptors triggers yawning, but that is an inference, not a finding. In the experience reports, yawning appears in descriptions of the come-up rather than the end of the experience. Evidence: unresolved.

Why do magic mushrooms cause chills, a faster heartbeat and higher blood pressure?

Health Canada lists increased heart rate and blood pressure, and sweating and high body temperature, often followed by chills and shivering (Health Canada). In the controlled crossover study, psilocybin moderately raised systolic and diastolic blood pressure, heart rate and body temperature compared with placebo; psilocybin raised diastolic pressure more than LSD did (Ley et al., 2023). The 2024 review estimated “hypertension” as an adverse event in 19.1% of psilocybin participants, a fast heart rate in 8.9% and feeling cold in 6.1%, each from small numbers of studies (Hinkle et al., 2024).

Tolerance is relevant here. The 2022 review notes that tolerance builds quickly to the psychedelic effects but has been reported not to build to autonomic effects such as pupil dilation, raised blood pressure, raised body temperature, goosebumps and a fast heart rate (Schlag et al., 2022).

“Not clinically significant” applies to screened, healthy volunteers. Health Canada says that for people with heart disease, the rise in blood pressure and heart rate could be harmful (Health Canada). Research guidelines also note that hallucinogens can moderately raise pulse and both systolic and diastolic blood pressure (Johnson et al., 2008). Evidence: established for healthy volunteers; the risk for people with heart conditions is flagged, not measured.

Why do shrooms make you sleepy or tired afterwards?

Tiredness is common in the data. The 2024 review estimated fatigue or weakness in 26.6% of psilocybin participants and sleepiness (somnolence) in 12.6% (Hinkle et al., 2024). Health Canada lists muscle weakness among short-term effects (Health Canada), and mushroom experience reports mention heaviness and lethargy (Brouwer et al., 2025).

The mechanism is not established, and no study we found has tested a cause. One research group notes that psychedelics have been shown to trigger the release of stress hormones, and compares the come-up to an acute stress reaction (Brouwer et al., 2025), but that is a description, not an explanation of later tiredness. In the controlled crossover study, psilocybin did not produce significant adverse effects in the 12 to 24 hours after dosing compared with placebo (Ley et al., 2023), and the trial meta-analysis reports acute effects resolving within 48 hours (Yerubandi et al., 2024). Our guide to how long magic mushrooms last covers timing and after-effects in more detail. Evidence: established that tiredness is commonly reported; the cause is unresolved.

Magic mushroom body effects at a glance

Rates in the table are from the 2024 review, except where a randomized trial is named (Hinkle et al., 2024; Yerubandi et al., 2024; Ley et al., 2023). The review notes that only 16 of 68 recent studies described a systematic way of collecting adverse events, so true rates could differ. For the mental effects, see magic mushroom effects, short and long term.

When are body symptoms a warning sign rather than a normal effect?

Vomiting and diarrhea that start hours later

Nausea from psilocybin tends to come early, during the come-up. Gut symptoms that begin many hours after eating a mushroom are a different matter. A medical review of mushroom poisoning notes that people looking for hallucinogenic mushrooms sometimes misidentify and eat more toxic ones, which can cause delayed symptoms and possibly organ failure. For amatoxin mushrooms, it describes a symptom-free period typically of 6 to 24 hours (reported up to 40 hours), then vomiting, watery diarrhea and abdominal pain, then an apparent recovery while liver damage continues (Graeme, 2014).

The Ontario Poison Centre says you may not become ill for many hours after eating a poisonous mushroom and not to wait until the person feels sick before calling (Ontario Poison Centre). Health Canada warns that many species look alike and that people can eat poisonous mushrooms by mistake (Health Canada). We cover this in magic mushroom misidentification and poisonous mushrooms in Ontario.

Signs of serotonin syndrome with some medicines

Serotonin syndrome is a drug-induced condition caused by too much serotonin activity, usually from drug interactions. Mild cases bring tremor and diarrhea; severe cases can bring delirium, rigid muscles, seizures, coma and very high body temperature. A 2025 scoping review of 18 studies found no increased risk of serotonin syndrome with antidepressants and psilocybin in those studies, but much of the evidence was case reports, surveys and open-label studies (Tap et al., 2025). Our guide to magic mushrooms and antidepressants covers what is known by medicine type. Do not stop or change a medicine on your own; ask a prescriber or pharmacist.

Chest pain, a pounding heart or a severe headache

A modest rise in heart rate is expected; chest pain is not. One case report describes a man taking the antidepressant tranylcypromine (an MAOI) and an amphetamine medicine who, about half an hour after eating psilocybin mushrooms, developed severe high blood pressure with chest pain, palpitations and headache. He was first diagnosed with a heart attack, though catheterization found no significant abnormality, and he went home without lasting harm. The authors suspect, without testing it, that another mushroom compound interacted with his medicines (Barnett et al., 2025). The poisoning review lists dysrhythmias and heart attack among reported events after hallucinogenic mushrooms (Graeme, 2014). These are rare reports, but chest pain, fainting or a severe headache warrant a 911 call.

Anxiety can feel physical too: the experience-report study notes that anxiety, attention to heartbeat and breathing, and nausea are common in stress reactions (Brouwer et al., 2025). If someone is in emotional crisis or thinking about suicide, the Government of Canada says to call or text 9-8-8, 24 hours a day (Government of Canada). Our guide to whether magic mushrooms are safe puts these risks in a wider frame.

What we still don’t know

• Exactly which receptors cause nausea after psilocybin, and whether other compounds in whole mushrooms add to it (unresolved).
• Why psilocybin causes yawning. Only three study groups reported it and no study has tested a mechanism (unresolved).
• How common each body effect is with mushrooms used outside studies, where amounts and contents are unknown (unresolved).
• What the heart effects mean for people with heart disease or high blood pressure, who are excluded from most trials (flagged by Health Canada, not measured).
• Why people feel tired afterwards, and how long it lasts outside trial settings (unresolved).

Research moves quickly, so check the date at the top of this page. For background, see what magic mushrooms are.

Shroomverse sells mushroom products. This article is general information about the physical effects recorded in research. It is not medical, legal or purchasing advice, and it does not recommend any product.