Where the answer is no
Some situations are not a matter of weighing risk against benefit. In responsible practice they are exclusions. A personal history of schizophrenia, schizoaffective disorder, or bipolar I. A first-degree family history of the same, particularly in a young person who has not yet passed through the typical age of onset. Uncontrolled hypertension or significant cardiac disease. Current use of an irreversible MAO inhibitor. Pregnancy. Active suicidal intent. Inability to give informed consent, for any reason.
These are not hedges. A person who screens into any of them should be told no, clearly and without a negotiation.
Cardiovascular
The acute experience typically involves a rise in blood pressure and heart rate. For a healthy cardiovascular system that is unremarkable. For an unhealthy one it is a stress test nobody ordered. Relevant history includes hypertension, arrhythmia, structural heart disease, prior myocardial infarction, stroke, aneurysm, and any anticoagulation.
Age alone is not a contraindication. Undiagnosed cardiovascular disease is, and the proportion of adults walking around with undiagnosed cardiovascular disease is not small. That is an argument for asking for recent clinical assessment rather than relying on how someone feels.
Psychiatric history
The concern with psychosis-spectrum illness is that a powerful serotonergic agent may precipitate or accelerate an episode in someone already vulnerable. The evidence base here is mostly extrapolated from other psychedelics and from case reports, and it is thin. The conservative position is the right one anyway, because the downside is severe and permanent in a way that the upside is not.
Trauma history is different. It is not an exclusion, and a great many people come precisely because of it. It does change what preparation and aftercare need to look like, and it raises the threshold for how much support has to be genuinely available afterwards rather than promised.
Dissociative disorders, current eating disorders, and recent psychiatric hospitalisation all warrant a clinical conversation before anything else happens.
Medications
A full medication review is not optional, and it has to include over-the-counter products and supplements. The categories that most often matter:
- MAO inhibitors, including the irreversible ones and including plant sources of harmala alkaloids. This is the most dangerous known interaction.
- SSRIs, SNRIs, tricyclics, lithium, and other serotonergic agents.
- St John's wort, which people frequently do not think of as a drug.
- Tramadol, dextromethorphan, and triptans, all serotonergic and all common.
- CYP2D6 inhibitors, which alter metabolism unpredictably between individuals.
- Stimulants, prescribed or otherwise.
Physical and situational risk
Loss of postural control is normal, which makes falls, head injury, and hard surfaces a foreseeable hazard. Vomiting with a compromised airway is an aspiration risk. Breath-holding and irregular respiration occur. Seizure has been reported. None of these require exotic circumstances to become serious.
Situational risk deserves the same attention. Isolation, distance from emergency medical care, absence of anyone medically trained, and no plan for escalation are all decisions, even when nobody consciously made them.
What a real intake covers
- Full medical history, with recent cardiovascular assessment where indicated.
- Full psychiatric history, personal and first-degree family.
- Complete medication and supplement list, including anything taken occasionally.
- Substance use history, including alcohol.
- What the person is hoping for, and whether that hope is realistic.
- What support exists in their life for the weeks afterwards.
- Capacity to consent, and whether anyone is pressuring them.
An intake that takes ten minutes is a formality rather than a screening. It exists to protect the person collecting the form.
Risk does not end when the effects do
The acute window is short. The period of instability afterwards is not. Prolonged derealisation, sleep disruption, mood swings, and difficulty functioning for days or weeks appear regularly in accounts. A minority experience something more serious and need clinical support.
Planning for that is part of the risk picture, not a separate topic. See integration.