New Study Indicates Cannabis-Associated Psychosis Risk Is Minimal

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May 1, 2008 - Albany, NY, USA

Albany, NY:

There is little increased risk of incidences of psychosis or

schizophrenia stemming from the use of cannabis, according to clinical

data to be published in the journal Human Psychopharmacology.


study found that participants who used cannabis, but no other illicit

substances did not score higher on a Schizotypal Personality

Questionnaire (SPQ) compared to those respondents who used legal drugs

only. However, those participants who used cannabis and other illicit

drugs such as ecstasy and cocaine did score higher on the SQP tests.

The study’s results contradict widely reported news reports alleging that marijuana use is associated with a much higher risk of psychosis.


previous work on the link between marijuana use and psychotic symptoms

has not controlled for other drug use at all," said NORML Advisory

Board member Mitch Earleywine,

who co-authored the study. "Other studies only use rough measures of

lifetime use of a few drugs. We focused on nine different drugs and

emphasized the stimulants, which work in a neurotransmitter system

linked closely to psychosis."

A prior review of cannabis and psychosis conducted by Britain’s Advisory Council on the Misuse of Drugs (ACMD) stated in a 2006 release

that, "the current evidence suggests, at worst, that using cannabis

increases lifetime risk of developing schizophrenia by one percent."


concurs with that assessment. "In my opinion, if cannabis has any

impact on psychosis at all it would only appear in folks who have a

genetic predisposition who also use heavily early in life," he said.

NORML published a white paper

last May which called for the regulation of cannabis as a means to

discourage its use by patients who may be predisposed to certain mental


Advocates for tougher marijuana laws in Britain have been trumpeting

the pot-and-psychosis link as a major impetus for Prime Minister Gordon

Brown’s expected move to elevate cannabis from a Class C to a Class B

drug. The ACMD declined

to back the move in a recent meeting on April 4, with 20 out of the

panel’s 23 experts deciding there was not sufficient new scientific

evidence to justify a change.

For more information, please contact NORML Deputy Director Paul Armentano at Full text of the study, "Polydrug Use, Cannabis Use, and Psychosis-Like Symptoms," will appear in Human Psychopharmacology.

    updated: May 01, 2008