Swiss researchers find the serotonin 2A receptors in the brain are involved in the psychotic (schizophrenia-like) effects of psilocybin in humans. The effects were blocked using the serotonin 2A agonist ketanserin and enhanced with the dopamine agonist haloperidol. “These data are consistent with animal studies and provide the first evidence in humans that psilocybin-induced psychosis is due to serotonin-2A receptor activation, independently of dopamine stimulation.” The authors suggest serotonin 2A overactivity may be involved in the pathology of schizophrenia and such agonists could be used as therapeutic agents.