Revealing shortcomings in the assessment of psilocybin effects on OCD-related symptoms in preclinical and clinical studies: a systematic review

Psilocybin is a chemical compound found in certain types of hallucinogenic mushrooms, known as magic mushrooms. Evidence has shown potential therapeutic effects of psilocybin on different neuropsychiatric disorders such as major depressive disorder (MDD), posttraumatic stress disorder (PTSD), anxiety disorders, and obsessive-compulsive disorder (OCD). Although the efficacy of psilocybin in alleviating OCD symptoms has been reported, evidence is very limited. The present study aimed to review the results of previous studies that examined the effects of psilocybin (or dried mushroom or extract) on OCD-related symptoms in humans and rodents. PubMed electronic database was searched and 268 articles were found. After removal of duplications and unrelated articles, 15 articles were included. All clinical studies (both case reports and clinical trials) showed the improvement of OCD symptoms. Preclinical studies using OCD-like models were rare. We also found some conflicting results in preclinical studies. We suggested that the potential role of the OCD test, OCD-like behavior, and the time interval between the test and psilocybin administration (or the follow-up duration) could be involved in the final effect of psilocybin. In conclusion, the present study showed shortcomings in the assessment of psilocybin effects on OCD-related symptoms. In future, we need more detailed studies on the effect of psilocybin in preclinical OCD-like models. The type of the behavioral test and the type of OCD-like behavior in rodents may also influence the effects of psilocybin and should be considered. Clinical studies with dozens of participants are also needed.