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Cannabis & psychosis - information for health care workers

What is the evidence that cannabis use is associated with psychosis?

It should be noted from the outset that:

That established, the following findings are noteworthy:

The risk of developing psychosis is believed to be increased by:

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What type of psychoses are associated with cannabis use?

It is believed that cannabis use may cause a condition known as a drug-induced psychosis or cannabis psychosis which:

However, in some cases, cannabis use may contribute to the development of a psychosis such as schizophrenia which:

Most of the research in this area has investigated cannabis in people with schizophrenia.

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Does cannabis use cause psychosis ?

However, of the conscripts who developed schizophrenia:

Therefore, cannabis use is only one possible factor contributing to an increased risk of developing schizophrenia or other psychosis. This is especially true when one considers that most people who develop a psychosis have never used cannabis

In addition, cannabis use at age 18 might be a consequence of emerging psychosis (that is, psychosis precedes cannabis use, not vice versa).

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How does cannabis use affect psychosis?

Do symptoms improve if a person with a psychosis stops using cannabis?

Who is most at risk from cannabis use?

What about the effect of other drugs?

Where can my clients turn for help?

If a person or client presents with psychotic symptoms, medical attention should be sought or provided immediately.

For confidential information and referral, friends and families can ring 1300 85 85 84, Monday-Friday 9AM-5PM, free call.

In addition, a single free copy of our Cannabis Diary can be obtained by contacting DrugInfo on 1300 85 85 84.

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Is any research currently being undertaken to investigate the link between cannabis use & psychosis?

The Victorian Government has funded research involving clinical and neurobiological studies, in an attempt to establish whether there is a link between cannabis use and psychosis.

Further reading

Andreasson, S. et al. 'Cannabis and schizophrenia: A longitudinal study of Swedish conscripts' Lancet, 2, 1483-1486, (1987).

Beaubruhn, M. and Knight, F. 'Psychiatric assessment of 30 chronic users of cannabis and 30 matched controls' American Journal of Psychiatry 130, 309-311, (1973).

Hambrecht, M. and Hafner, H. 'Substance use and the onset of schizophrenia' Biological Psychiatry 40, 1155-1163, (1996).

Hall, W. Cannabis Use and Psychosis National Drug and Alcohol Research Council Sydney Australia (1997).

Imade, A.G.T. and Ebie, J.C. 'A retrospective study of symptom patterns of cannabis-induced psychosis' Acta Pyschiatrica Scandinavia 83, 134-136, (1991).

Jerrell, J. and Ridgely, M.S. 'Comparative effectiveness of three approaches to serving people with severe mental illness and substance abuse disorders' Journal of Nervous and Mental Disease ; 183, 566-576, (1995).

Linszen, D.H., et al. 'Cannabis use and the course of recent-onset schizophrenic disorders' Archives of General Psychiatry 51, 273-279, (1994).

Mathers, D.C. et al. 'Cannabis use in a large sample of acute psychiatric admissions' British Journal of Addiction 86: 779-784, (1991).

McGuire P. et al. 'Cannabis and acute psychosis' Schizophrenia Research , 13: 161-168, (1994).

McGuire P. et al. 'Morbid risk of schizophrenia for relatives of patients with cannabis associated psychosis' Schizophrenia Research , 15, 277-281, (1995).

Mueser, K.T. 'Comorbidity and substance abuse: Implications for treatment' Journal of Consulting and Clinical Psychology 60, 845-856, (1992).

Rolfe, M. et al.’ Psychosis and cannabis abuse in The Gambia: A case control study' British Journal of Psychiatry 163, 789-801, (1993).

Rottanburg, D. et al. 'Cannabis-associated psychosis with hypomanic features' Lancet , 2, 1364-1366, (1982).

Thacore, V.R. and Shukla, S.R.P. 'Cannabis Psychosis and Paranoid Schizophrenia' Archives of General Psychiatry 33, 383-386, (1976).

Thornicroft, G. 'Cannabis and psychosis: Is there epidemiological evidence for association?' British Journal of Psychiatry 157, 25-33, (1990).

Tien, A.Y. and Anthony, J.C. 'Epidemiological analysis of alcohol and drug use as risk factors for psychotic experiences' Journal of Nervous and Mental Disease 178: 473-480, (1990).

Acknowledgements

The booklet (which was basis for this page) has been based on the report entitled, Cannabis Use and Psychosis (1997) by Professor Wayne Hall of the National Drug and Alcohol Research Centre, Sydney, Australia.

The NDARC report was initially modified into booklet form by the Drug Wise consultancy and subsequently developed and refined by the Expert Reference Group on Cannabis and Psychosis.