Who Is NOT a Suitable Candidate for Psilocybin Therapy, and What Are the Medical Risks or Contraindications?

Psilocybin-assisted therapy has emerged as a promising treatment for treatment-resistant depression, but it is not suitable for everyone. Strict clinical and legal safeguards exist to protect patients from potential harm, and certain conditions, medications, and personal histories can make this therapy unsafe or ineffective. Consequently, understanding who is excluded and what risks exist is essential for anyone considering this treatment.

Absolute Contraindications: Who Cannot Access Psilocybin Therapy

Clinical guidelines identify several absolute exclusion criteria for psilocybin therapy. Patients with these conditions are not eligible for treatment due to the significant risk of severe adverse events.

Personal or Family History of Psychotic Disorders

A personal history of a psychotic episode, schizophrenia, or schizoaffective disorder is an absolute contraindication for psilocybin therapy . Furthermore, having a first-degree relative (parent, sibling, or child) with schizophrenia, schizoaffective disorder, or a psychotic disorder also excludes patients from treatment . Psilocybin can exacerbate or trigger psychotic symptoms in individuals predisposed to these conditions .

Personal or Family History of Bipolar Disorder

A personal history of a manic episode or a first-degree relative with Bipolar I disorder is also an absolute contraindication . Psilocybin may induce manic episodes in individuals with bipolar disorder or those at risk .

Pregnancy and Breastfeeding

Women who are pregnant or breastfeeding should avoid psilocybin therapy due to the lack of evidence regarding its safety for the foetus or infant . Clinical trials routinely exclude pregnant or breastfeeding individuals .

Uncontrolled Cardiovascular Conditions

Psilocybin can elevate blood pressure and increase heart rate. Consequently, patients with serious or uncontrolled cardiovascular conditions, including uncontrolled hypertension and clinically significant cardiac disease, are not suitable candidates .

Medical Conditions Requiring Caution or Exclusion

The following conditions may not be absolute exclusions in all cases but require careful clinical assessment and may render patients ineligible.

Severe Renal or Hepatic Impairment

Individuals with severe renal insufficiency or markedly abnormal liver function tests may be excluded due to the body’s reduced ability to process and eliminate the drug .

Severe Pulmonary Disease

Patients with severe pulmonary disease or those requiring supplemental oxygen are typically excluded due to the physical demands and potential respiratory effects of the therapy .

Active Substance Use Disorder

An active substance use disorder is generally considered an exclusion criterion . This ensures that patients are stable and able to engage fully in the therapeutic process without the confounding effects of other substances.

Suicidality and Self-Harm

Patients with a history of serious suicide attempts (requiring hospitalisation) or active suicidal ideation may be excluded, particularly in clinical trial settings . While psilocybin does not cause lasting psychosis, the vulnerability induced by the altered state requires careful screening . Systematic reviews have noted that suicidal ideation and behaviour have been observed infrequently in clinical trials, mainly in participants with a history of such thoughts or attempts .

Medication Interactions and Washout Periods

Patients taking certain medications may not be suitable for psilocybin therapy unless they can safely discontinue them.

Serotonergic Medications

Patients taking SSRIs or other medications that affect serotonin levels (including some antidepressants, appetite suppressants, and anti-anxiety medications) will need to be free of these for a minimum of 4–8 weeks before a psilocybin session can occur . For some individuals, discontinuing these medications is not clinically advisable, making psilocybin therapy unavailable .

Lithium and Mood Stabilisers

Concurrent use of lithium, which is commonly prescribed for bipolar disorder, may increase the risk of seizures and is a contraindication for psilocybin therapy .

Antipsychotics

Patients taking antipsychotic medications are generally excluded from psilocybin therapy, as these drugs can blunt the effects of psilocybin and may interact dangerously .

Common Physical and Psychological Risks

Even for suitable candidates, psilocybin-assisted therapy carries risks that must be weighed against potential benefits.

Physical Adverse Effects

Short-term effects: The most common adverse effects are transient and include elevated blood pressure, headache, nausea, vomiting, fatigue, and dizziness . In a systematic review of clinical trials, these were the most frequently reported physical adverse events during and after psilocybin sessions .

Microdosing side effects: For those considering microdosing, common side effects include increased blood pressure, anxiety, and cognitive impairment, though these are typically dose-dependent, mild, and short-lived .

Psychological Adverse Effects

Challenging experiences (“bad trips”): Acute psychological distress during the session is common and can include intense and overwhelming anxiety, fear, paranoia, panic, and a sense of losing touch with reality . In a survey study, 31% of respondents reported experiencing periods of acute anxiety during psilocybin use .

Persisting negative effects: Approximately 22.5% of LSD and psilocybin users reported at least one negative outcome, with the most common being “mental confusion, memory problems, or racing thoughts” . 6% of users reported difficulties lasting longer than one month .

Functional impairment: Research suggests 9-13% of non-clinical trial psychedelic users have experienced negative outcomes involving functional impairment in the days or weeks after dosing . 7.6% of psilocybin users who had challenging experiences sought treatment for persistent psychological symptoms .

Suicidal ideation: Infrequent instances of suicidal ideation and behaviour have been reported in clinical trials, primarily in participants with a history of such thoughts or attempts . One study found that 2.6% of users experienced suicidal ideation and 1.9% engaged in intentional self-harm .

Australian Clinical Practice: Screening and Assessment

In Australia, eligibility for psilocybin therapy is determined through a rigorous clinical assessment process. Authorised psychiatrists are responsible for screening patients and ensuring all TGA-approved treatment options have been exhausted before considering psilocybin . The Australian Psychological Society emphasises that psychologists and health professionals involved in this therapy must understand for whom it may be suitable or unsafe . A study in Sydney found that in a clinical trial for methamphetamine use disorder, 56 participants were pre-screened, but only 15 met the eligibility criteria and enrolled . This demonstrates the stringent nature of patient selection.

Conclusion

Psilocybin-assisted therapy is not a treatment for everyone. Absolute contraindications include personal or family history of psychotic disorders, bipolar disorder, pregnancy, and uncontrolled cardiovascular conditions. Patients on certain serotonergic or psychiatric medications must undergo a washout period or may be excluded entirely. Common risks include transient physical effects like headache and nausea, as well as psychological risks such as anxiety and, in rare cases, suicidal ideation. In Australia, strict clinical assessments ensure that only carefully screened patients with treatment-resistant depression have access to this therapy. This guide is for educational and research purposes only and does not constitute legal or medical advice. If you are considering psilocybin therapy, the first step is to discuss your situation with a General Practitioner, who can refer you to a suitably qualified psychiatrist.