Who should not attend a psilocybin retreat: screening, medications and contraindications

In Colorado's regulated program, screening is a legal requirement, not a formality. Facilitators must use a safety screening tool that reflects generally accepted standards of practice. They must review your medical history, and they must ask you to confirm that what you have shared is complete and accurate. If they find a risk factor, they can only go ahead after a referral, medical clearance, or a consultation and risk review with a qualified provider. Any facilitator may decline to work with someone for any health or safety reason.

This is the most important area. In their widely cited 2008 safety guidelines, researchers at Johns Hopkins excluded people with a current or past history of schizophrenia or other psychotic disorders, and people with bipolar I or II disorder. They called these "the most important conditions to exclude for ensuring safety". They also excluded anyone with a first- or second-degree relative with these conditions.

What this means for you: if you or a close family member have been diagnosed with schizophrenia, another psychotic disorder, or bipolar disorder, expect careful screening, and expect that a psilocybin retreat may not be appropriate. Be open about family history, even if it feels distant.

Lithium. Colorado's rules name lithium directly. A facilitator may not work with someone taking lithium or antipsychotic medication unless there has been a referral, medical clearance, or a consultation and risk review. A clinical facilitator who does not prescribe these medications needs the same clearance or consultation. The research reason is serious. In a 2021 analysis of online reports, 47% of 62 reports of a classic psychedelic taken with lithium involved seizures. The authors concluded that psychedelic use "may pose a significant seizure risk for patients on lithium."

Antipsychotics. These are named alongside lithium in Colorado's rules, with the same conditions.

SSRIs and SNRIs (common antidepressants). The concern here is different. These medications may *blunt* psilocybin's effects. In a 2023 survey study, people taking SSRIs or SNRIs often reported weaker effects than expected, and the dampening may last up to three months after stopping. This is not a reason to stop your antidepressant. Stopping these medications can cause withdrawal and a return of symptoms. Any change must be planned with your prescriber, never on your own to fit a retreat date.

Other medications. The 2008 Johns Hopkins guidelines also flagged tricyclic antidepressants and MAO inhibitors, which can change how the body responds to psychedelics. Bring a complete list of everything you take, including supplements, to screening.

Heart and blood pressure. Psilocybin moderately raises pulse and blood pressure. In Johns Hopkins studies, volunteers were excluded if their resting blood pressure was above 140/90. Colorado's rules list cardiovascular disease and uncontrolled hypertension among the conditions where a clinical facilitator must contact your treating provider before going ahead, unless there is good cause not to.

Seizure disorders, liver disease, severe or terminal illness. Colorado's rules name these too. Each one means coordination with your treating provider first.

Pregnancy and breastfeeding. Clinical trials of psychedelics routinely exclude people who are pregnant, planning a pregnancy, or breastfeeding. A 2025 review of trial exclusion criteria notes that it remains unclear whether classic psychedelics pass into breast milk. The safety of psilocybin in pregnancy has not been established. If you are pregnant, trying to conceive, or breastfeeding, a psilocybin retreat is not appropriate.

Not every reason to wait is medical. You may want to pause if:

• you are in an acute crisis, or have recently had thoughts of suicide (if so, please call or text 988 now)
• you cannot commit to preparation and integration
• you feel pressured by someone else to go
• you expect the experience to fix something specific, quickly

A good facilitator will talk with you about this openly. Colorado's rules require facilitators to discuss your goals and whether they can reasonably be met.

A "no" or "not yet" is the screening process doing its job. Depending on what comes up, the next step might be a conversation with your own doctor, a medication review with your prescriber, or simply waiting. If you need clearance, Colorado's rules accept a provider licensed in your home state.

Where clearance comes after a consultation and risk review that finds a heightened risk, the rules add a further step. You and the facilitator must develop a safety plan informed by that review, and you must give written informed consent before going ahead. That plan is worth taking seriously. It is the point where your own provider's knowledge of you meets the facilitator's knowledge of the session.

The most useful thing you can do is be completely honest at screening, including about things that feel minor or long ago.

For how this works on Maureen Lennon-Schafer's retreat, see our safety page and the Boulder retreat page. For the legal background, read the Colorado psilocybin guide.

Halcyon does not provide medical services and does not diagnose or treat any condition. Clinical services are provided by licensed professionals through our partner, Presence of Mind Therapy.