Psilocybin is a substance, found in some species of North American mushrooms, that can cause extended hallucinatory events (Lowe 2021). Side effects of psilocybin use include nausea, vomiting, muscle weakness, headache, higher blood pressure, fear or paranoia, and reduction in coordination (US DEA 2020).
Repeated psilocybin use can result in users needing higher doses over time to have the same effect.
Like many psychoactive substances, psilocybin is classified under Schedule 1 of the federal Controlled Substances Act. Drug scheduling by the Drug Enforcement Agency, the Food and Drug Administration, and Congress determines levels of restriction and regulation.
While states largely mimic federal drug restrictions, some states have recently legalized the recreational and/or medicinal use of specific substances (e.g., cannabis, psilocybin) (NCSL 2022). Read our Science Note on Cannabis Legalization for more information on state policies that limit or regulate cannabis use.
In 2018, the Food and Drug Administration (FDA) designated psilocybin as a “Breakthrough Therapy,” which allows for the development and review of drugs that provide a substantial improvement over current options (Bird 2021).
In 2019, private investors spent more than $420 million on research and development for psychedelic drug treatments for several neurological disorders.
Table 1 describes the range of disorders that psilocybin treatment is being researched for.
Given the limited legal use, no large-scale or long-term studies exist to make strong conclusions about therapeutic psilocybin.
Some studies suggest that psilocybin can treat post-traumatic stress disorder (PTSD). However, no robust clinical research has confirmed its short- and long-term efficacy (Bird 2021).
There is stronger evidence that psilocybin use can lead to long-term improvements in depression and general anxiety, particularly in chronic or terminally ill patients (Lowe 2021).
In a small-scale toxicity study (18 patients), male, long-term AIDS survivors given two doses of psilocybin and multiple group therapy sessions (over 18 hours) had reduced rates of PTSD and depression (Khan 2022; Abbas 2021).
Interviews with small veterans' groups sug-gest that psilocybin can cause unique short- and long-term changes in how the brain processes and adapts to trauma, which can reduce PTSD symptoms (Smith 2022).
In medium-scale efficacy trials (20 patients), patients with treatment-resistant depression had fewer symptoms after psilocybin use (42-54% reduction) as early as a week after treatment (Gill 2020; Abbas 2021).
Bird, C. I. V., Modlin, N. L., & Rucker, J. J. H. (2021). Psilocybin and MDMA for the treatment of trauma-related psychopathology. International Review of Psychiatry, 33(3), 229-249. doi:10.1080/09540261.2021.1919062
The Controlled Substances Act (CSA): A Legal Overview for the 116th Congress. (2019). Retrieved from https://crsreports.congress.gov/product/pdf/R/R45948/1
Drug Fact Sheet: Psilocybin. (2020). Retrieved from https://www.dea.gov/sites/default/files/2020-06/Psilocybin-2020_0.pdf
Gill, H., Gill, B., Chen-Li, D., El-Halabi, S., Rodrigues, N. B., Cha, D. S., . . . McIntyre, R. S. (2020). The emerging role of psilocybin and MDMA in the treatment of mental illness. Expert Review of Neurotherapeutics, 20(12), 1263-1273. doi:10.1080/14737175.2020.1826931
Goldberg, S. B., Pace, B. T., Nicholas, C. R., Raison, C. L., & Hutson, P. R. (2020). The experimental effects of psilocybin on symptoms of anxiety and depression: A meta-analysis. Psychiatry Research, 284, 112749. doi:10.1016/j.psychres.2020.112749
Hartman, M. (2022). Cannabis Overview. Retrieved from https://www.ncsl.org/civil-and-criminal-justice/cannabis-overview#legalization
Johnson, M. W., Griffiths, R. R., Hendricks, P. S., & Henningfield, J. E. (2018). The abuse potential of medical psilocybin according to the 8 factors of the Controlled Substances Act. Neuropharmacology, 142, 143-166. doi:https://doi.org/10.1016/j.neuropharm.2018.05.012
Khan, A. J., Bradley, E., O’Donovan, A., & Woolley, J. (2022). Psilocybin for Trauma-Related Disorders. In F. S. Barrett & K. H. Preller (Eds.), Disruptive Psychopharmacology (pp. 319-332). Cham: Springer International Publishing.
Lowe, H., Toyang, N., Steele, B., Valentine, H., Grant, J., Ali, A., . . . Gordon, L. (2021). The Therapeutic Potential of Psilocybin. Molecules, 26(10). doi:10.3390/molecules26102948
Mithoefer, M. C., Grob, C. S., & Brewerton, T. D. (2016). Novel psychopharmacological therapies for psychiatric disorders: psilocybin and MDMA. Lancet Psychiatry, 3(5), 481-488. doi:10.1016/s2215-0366(15)00576-3
Smith, F., Neill, J., & Wainwright, V. (2022). An Interpretative Phenomenological Analysis of the use of psilocybin by veterans with symptoms of trauma. Drug Science, Policy and Law, 8, 20503245221124117. doi:10.1177/20503245221124117