Adverse Effects

While there is a wide array of adverse effects, the adverse effects depend on the dose level and can vary significantly from person to person.

As with its psychological effects, psilocybin also has physical effects on the human body; though these may also present risks at times, the psychological risks of the substance are seen as being more likely to occur (Johnson et al., 2008).

The adverse effects listed in this section are not an exhaustive list, however they are the most common adverse effects or the adverse effects that cause the greatest concern in a clinical setting.

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Vital Signs

Psilocybin is not known to have a big impact on a client’s vital signs, however it can impact the following:

Psilocybin was shown to have no effects on ECG or body temperature (Hasler et al., 2004).

Physical Adverse Effects

Some other physical adverse effects of psilocybin or psilocin administration include:

  • Mydriasis

  • Blurred vision

  • Paresthesia

  • Drowsiness

  • Yawning

  • Tremor

  • Weakness

  • Dizziness

  • Increased tendon reflexes

  • Nausea

  • Vomiting

  • Acute and delayed headaches (Griffiths et al., 2006; Hasler et al., 2004; Isbell, 1959; Hollister, 1961; Johnson et al., 2008; Peden & Pringle, 1982; Rush et al., 2022)

Note

As with any medication, the potential for unexpected allergic reactions exists.

Note

Nausea and vomiting are usually associated with the ingestion of psilocybin-producing mushrooms rather than the administration of psilocybin or psilocin (Hollister, 1961; Johnson et al., 2008; Peden & Pringle, 1982).

Behavioural Adverse Effects

Psilocybin may produce some behavioural adverse effects including:

  • Anxiety

  • Panic

  • Dysphoria

  • Depersonalization

  • Paranoia

  • Agitation

  • Acute psychotic reactions

  • Fear that the experience will never end

  • Fear of losing one’s mind

  • Erratic behaviour (Rush et al., 2022; Grob & Grigsby, 2022; Studerus et al., 2011)

References

Grob, C. S. & Grigsby, J. (2022). Handbook of Medical Hallucinogens. Guildford Press.

Griffiths, R. R., Richards, W. A., McCann, U., & Jesse, R. (2006). Psilocybin can occasion mystical-type experiences having substantial and sustained personal meaning and spiritual significance. Psychopharmacology, 187(3), 268-283.

Hasler, F., Grimberg, U., Benz, M. A., Huber, T., & Vollenweider, F. X. (2004). Acute psychological and physiological effects of psilocybin in healthy humans: a double-blind, placebo-controlled dose- effect study. Psychopharmacology (Berl), 172(2), 145-156. https://doi.org/10.1007/s00213-003- 1640-6

Hollister, L. E. (1961). Clinical, biochemical and psychologic effects of psilocybin. Arch Int Pharmacodyn Ther, 130, 42-52.

Isbell, H. (1959). Comparison of the reactions induced by psilocybin and LSD-25 in man. Psychopharmacologia, 1, 29-38. https://doi.org/10.1007/BF00408109

Johnson, M., Richards, W., & Griffiths, R. (2008). Human hallucinogen research: guidelines for safety. J Psychopharmacol, 22(6), 603-620. https://doi.org/10.1177/0269881108093587

Peden, N. R., & Pringle, S. D. (1982). Hallucinogenic fungi. Lancet, 1(8268), 396-397. https://doi.org/10.1016/s0140-6736(82)91422-2

Rush, B., Marcus, O., Shore, R., Cunningham, L., Thomson, N., and Rideout, K. (2022). Psychedelic Medicine: A Rapid Review of Therapeutic Applications and Implications for Future Research. Homewood Research Institute. https://hriresearch.com/research/exploratory- research/research-reports/

Studerus, E., Kometer, M., Hasler, F., & Vollenweider, F. X. (2011). Acute, subacute and long-term subjective effects of psilocybin in healthy humans: a pooled analysis of experimental studies. Journal of psychopharmacology (Oxford, England), 25(11), 1434–1452. https://doi.org/10.1177/0269881110382466