New Study: Marijuana Causes Psychosis

February 08, 2011 CNN

Psychopharmacology (Berl). 2012 Mar 9. [Epub ahead of print]

Delayed preattentional functioning in early psychosis patients with cannabis use.


School of Psychology, University of Wollongong, Wollongong, NSW, 2522, Australia,



Cannabis use is prevalent among the early psychosis (EP) population. The event-related potentials, mismatch negativity (MMN) and P3a are reduced in EP. Cannabinoids have been shown to modulate N-methyl-D-aspartate receptors which are involved in MMN generation.


This study is the first to investigate the effects of cannabis use on MMN/P3a in EP.


EP was defined as a history of psychosis or psychotic symptoms with no progression to date to chronic schizophrenia. Twenty-two EP patients with cannabis use (EP + CANN), 22 non-cannabis-using EP patients (EP-CANN) and 21 healthy controls participated in this study. MMN/P3a was elicited using a two-tone, auditory paradigm with 8% duration deviants.


As expected, EP-CANN showed marked reductions in MMN/P3a amplitudes compared to controls. However, EP + CANN showed evidence of a different pattern of neurophysiological expression of MMN/P3a compared to non-using patients, most notably in terms of delayed frontal MMN/P3a latencies.


This study provides further evidence that MMN/P3a deficits are present during early psychosis and suggests that this biomarker may have utility in differentiating substance- from non-substance-related psychoses.


Marijuana-induced mania in a healthy adolescent: a case report.

Gen Hosp Psychiatry. 2011 May 27. [Epub ahead of print]
Iskandar JW, Griffeth B, Sharma T.


Carilion Clinic-Virginia Tech Carilion School of Medicine Psychiatry Residency Program, Roanoke, VA 24014, USA.


Marijuana is the most commonly used illegal substance by adolescents in the United States. According to a 2009 survey conducted by Monitoring the Future, there were about 11.8% of 8th graders, 26.7% of 10th graders and 32.8% of 12th graders who had abused marijuana at least once in the year (Johnston L.D., Bachman J.G., O’Malley P.M., Schulenberg J.E. Monitoring the Future: A Continuing Study of American Youth (12th-Grade Survey), 2009 [Computer file]. ICPSR28401-v1. Ann Arbor, MI: Interuniversity Consortium for Political and Social Research [distributor], 2010-10-27. doi:10.3886/ICPSR28401). A retrospective review of published literature disclosed case reports of marijuana-induced mania in adult patients with no prior psychiatric history (Bonnet U., Chang D.I., Wiltfang J., Scherbaum N., Weber R. A case of cannabis-induced mania. Fortschr Neurol Psychiatr. 2010 Apr; 78(4):223-5. Epub 2010 Feb3; Henquet C., Krabbendam L., de Graaf R., ten Have M., van Os J. Cannabis use and expression of mania in the general population. J Affect Disord. 2006 Oct;95(1-3):103-10. Epub 2006 Jun 21). To the best of our knowledge, this is the first report to document that marijuana induced manic symptoms in an adolescent with no known prior psychiatric history.

Copyright © 2011 Elsevier Inc. All rights reserved.

Cannabis-associated psychosis with hypomanic features.

Lancet. 1982 Dec 18;2(8312):1364-6.


The mental state of 20 psychotic men with high urinary cannabinoid levels on admission to a psychiatric hospital was compared with that of 20 matched cannabis-free controls. All patients underwent toxicological analysis to exclude the presence of alcohol and other exogenous agents.

Cannabis levels were measured by a semiquantitative enzyme immunological technique and mental state was assessed by the use of the Present State Examination (PSE), once shortly after admission and again 7 days later. The cannabis group showed significantly more hypomania and agitation and significantly less affective flattening, auditory hallucinations, incoherence of speech, and hysteria than did the controls.

Clouding of consciousness was absent in most cannabis patients. After 1 week the cannabis group showed marked improvement (particularly in the psychotic syndromes), whereas the controls remained virtually unchanged. There was no significant difference in amount of medication received between the two groups.

Our data suggest that a high intake of cannabis may be related to a rapidly resolving psychosis manifesting with marked hypomanic features, though often presenting as a schizophrenia-like illness.

[PubMed – indexed for MEDLINE]

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