Long-term use was associated with thinning of the posterior cingulate cortex , thickening of the anterior cingulate cortex , and decreased neocortical 5-HT2A receptor binding .
Despite the high method ological heterogeneity and the small sample sizes , the results suggest that hallucinogens increase introspection and positive mood by modulating brain activity in the fronto-temporo-parieto-occipital cortex
Serotonergic hallucinogens produce alterations of perceptions , mood , and cognition , and have anxiolytic , antidepressant , and antiaddictive properties .
These drugs act as agonists of frontocortical 5-HT2A receptors , but the neural basis of their effects are not well understood .
Thus , we conducted a systematic review of neuroimaging studies analyzing the effects of serotonergic hallucinogens in man .
Safety, tolerability, and efficacy of psilocybin in 9 patients with obsessive-compulsive disorder.
BACKGROUND Anecdotal reports suggest that psychedelic agents may relieve symptoms of  obsessive-compulsive disorder ( OCD ) . This modified double-blind study investigated the safety , tolerability , and clinical effects of psilocybin , a potent 5-HT(1A ) and 5-HT(2A/2C ) agonist , in patients with OCD . METHOD Nine subjects with DSM-IV-defined OCD and no other current major psychiatric disorder participated in up to 4 single-dose exposures to psilocybin in doses ranging from sub-hallucinogenic to frankly hallucinogenic . Low ( 100 microg/kg ) , medium ( 200 microg/kg ) , and high ( 300 microg/kg ) doses were assigned in that order , and a very low dose ( 25 microg/kg ) was inserted r and omly and in double-blind fashion at any time after the first dose . Testing days were separated by at least 1 week . Each session was conducted over an 8-hour period in a controlled environment in an outpatient clinic ; subjects were then transferred to a psychiatric inpatient unit for overnight observation . The Yale-Brown Obsessive Compulsive Scale ( YBOCS ) and a visual analog scale measuring overall obsessive-compulsive symptom severity were administered at 0 , 4 , 8 , and 24 hours post-ingestion . The Hallucinogen Rating Scale was administered at 8 hours , and vital signs were recorded at 0 , 1 , 4 , 8 , and 24 hours after ingestion . The study was conducted from November 2001 to November 2004 . RESULTS Nine subjects were administered a total of 29 psilocybin doses . One subject experienced transient hypertension without relation to anxiety or somatic symptoms , but no other significant adverse effects were observed . Marked decreases in OCD symptoms of variable degrees were observed in all subjects during 1 or more of the testing sessions ( 23%-100 % decrease in YBOCS score ) . Repeated- measures analysis of variance for all YBOCS values revealed a significant main effect of time on Wilks lambda ( F = 9.86 , df = 3,3 ; p = .046 ) , but no significant effect of dose ( F = 2.25 , df = 3,3 ; p = .261 ) or interaction of time and dose ( F = 0.923 , df = 9,45 ; p = .515 ) . Improvement generally lasted past the 24-hour timepoint . CONCLUSIONS In a controlled clinical environment , psilocybin was safely used in subjects with OCD and was associated with acute reductions in core  OCD symptoms in several subjects
Long-term use was associated with thinning of the posterior cingulate cortex , thickening of the anterior cingulate cortex , and decreased neocortical 5-HT2A receptor binding .
Despite the high method ological heterogeneity and the small sample sizes , the results suggest that hallucinogens increase introspection and positive mood by modulating brain activity in the fronto-temporo-parieto-occipital cortex
Serotonergic hallucinogens produce alterations of perceptions , mood , and cognition , and have anxiolytic , antidepressant , and antiaddictive properties .
These drugs act as agonists of frontocortical 5-HT2A receptors , but the neural basis of their effects are not well understood .
Thus , we conducted a systematic review of neuroimaging studies analyzing the effects of serotonergic hallucinogens in man .