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Body mass index (BMI) does not predict responses to psilocybin

Summary

Researchers investigated whether a person’s body weight affects how they respond to psilocybin-assisted therapy. Analyzing 77 participants across three studies, they found that BMI did not predict how intensely people experienced the drug or how much their mental health improved afterward. This surprising finding suggests that everyone might benefit from the same fixed dose of psilocybin rather than doses adjusted to body weight, making therapy simpler and more cost-effective to deliver at scale.

Background

Psilocybin is a serotonin 5-HT2A receptor agonist and naturally occurring psychedelic. 5-HT2A receptor density is associated with body mass index (BMI), and body weight-adjusted dosing is widely used in psychedelic research. However, the impact of BMI on psilocybin therapy has not been explored, creating a gap between evidence and clinical practice.

Objective

To assess whether BMI predicts characteristics of the acute psilocybin experience and long-term psychological outcomes using a fixed 25 mg dose. The study aimed to clarify the relationship between BMI and therapeutic response to inform dosing strategies for large-scale psychedelic-assisted therapy.

Results

BMI did not predict overall intensity of altered state, mystical experiences, perceptual changes, or emotional breakthroughs during acute psilocybin experience. Weak evidence suggested greater dread of ego dissolution in lower BMI participants, but study design was the primary driver of this effect. Mystical-type experiences and emotional breakthroughs predicted improvements in well-being, but BMI did not.

Conclusion

These findings provide strong evidence that BMI does not predict acute or long-term psychological responses to a fixed 25 mg psilocybin dose. The results support standardization of fixed therapeutic dosing rather than weight-adjusted dosing, with important implications for large-scale implementation of psychedelic-assisted therapy and simplification of clinical trial design.
  • Published in:Journal of Psychopharmacology,
  • Study Type:Pooled Analysis,
  • Source: 10.1177/02698811221131994, PMID: 36373934
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