Nausea, risks and safety

Nausea is the effect people mention first. The Alcohol and Drug Foundation lists "intense nausea and vomiting" among the typical effects of mescaline (ADF), and the bulky, bitter plant material adds to it.

Plan for it instead of fighting it:

• Have a bucket or bowl, tissues and water within reach, and know where the toilet is.
• Drink water in small sips; large amounts at once tend to come back up.
• Fresh air and a quiet place to lie down make the first hours easier to sit through.
• Vomiting during this phase is common. It is a reason for concern only when it does not stop, when someone cannot keep any fluid down for hours, or when they are drowsy and hard to wake.

If someone is very drowsy and vomiting, turn them on their side so they cannot choke, stay with them and call the emergency number.

The mescaline content of San Pedro and its relatives varies from 0.053% to 4.7% of dry weight, a factor of almost 100 (Ogunbodede et al. 2010). The species on the label, the size of the plant and its colour tell you nothing reliable. Someone else's experience with "a piece this big" does not transfer to another plant.

Two rules follow from this. Assume every new plant is an unknown. And never take a second portion early: the effects can take up to two hours to appear (ICEERS), so an early top-up can double a peak that has not yet arrived.

Mescaline raises blood pressure, heart rate and body temperature. In the Basel study the rises were moderate in healthy volunteers (Ley et al. 2023); a pharmacology review describes the bodily signs as consistent with a sympathomimetic effect, the same family of effects that stimulants produce. That is a real risk for people with heart disease, high blood pressure or other cardiovascular problems, and it adds up with heat and exertion.

Stay out of strong sun and heat, wear layers that can come off, and drink water regularly without overdoing it. Long walks or physical work during the peak are a bad idea.

ICEERS advises that people with a history of psychotic disorders, bipolar disorder or suicidal thoughts should not use mescaline outside a clinical research setting. A long and intense altered state can be destabilising for exactly these people.

Others who should not take it:

• anyone under 18
• anyone who is pregnant or breastfeeding
• anyone with heart disease or high blood pressure
• anyone taking the medicines in the next section
• anyone who has to look after children or work within the next 24 hours

• Lithium. An analysis of online reports found seizures in 47% of 62 accounts that combined lithium with a classic psychedelic, and medical attention in 39% (Nayak et al. 2021). Do not combine them.
• Tramadol. The Alcohol and Drug Foundation warns that mescaline with tramadol lowers the seizure threshold.
• Cannabis. Anecdotal reports describe a more intense and more often difficult experience when the two are combined.
• Other prescription medicines and other drugs. Interactions with mescaline are poorly studied. Ask a pharmacist about anything you take regularly, and do not mix it with alcohol or stimulants.

A sober companion who knows what was taken is the single most useful precaution. The place should be familiar, private and quiet, with access to fresh air and a way to stay warm or cool down. Avoid crowds, traffic and anywhere you might be disturbed. In Basel, volunteers named music and nature as the factors that made a session go well and a sterile, unfamiliar room as the most unpleasant (Ley et al. 2025).

If someone becomes very anxious or confused, move to a calmer place, keep the lights soft, speak calmly and remind them that the effect is temporary and will pass. Stay with them. Call for medical help with chest pain, a seizure, a very high temperature, fainting, or if someone is a danger to themselves.

Headache and tiredness in the 12 to 24 hours after mescaline were more common than after LSD or psilocybin in the Basel comparison. The ADF also lists anxiety, poor appetite, aches and difficulty sleeping during the come-down. Keep the next day free, eat when appetite returns, and do not drive until you are fully back to normal.

• Free day plus the following day, no driving
• Sober companion present throughout
• No lithium, no tramadol, no other psychedelics or alcohol
• Water, a bucket and somewhere to lie down
• No second portion within the first two hours
• Know the emergency number and say honestly what was taken

For the timeline itself, see effects and duration.