Washington: Cannabis and heavy methamphetamine users might have a higher risk of developing schizophrenia, according to Canadian scientists.
This finding by scientists from Toronto’s Centre for Addiction and Mental Health (CAMH) was based on a large study comparing the risk among methamphetamine users not only to a group that did not use drugs, but also to heavy users of other drugs.
Methamphetamine and other amphetamine-type stimulants are the second most common type of illicit drug used worldwide.
“We found that people hospitalised for methamphetamine dependence who did not have a diagnosis of schizophrenia or psychotic symptoms at the start of our study period had an approximately 1.5 to 3.0-fold risk of subsequently being diagnosed with schizophrenia, compared with groups of patients who used cocaine, alcohol or opioid drugs,” said Dr. Russ Callaghan, the CAMH scientist who led the study.
Dr. Callaghan also found that the increased risk of schizophrenia in methamphetamine users was similar to that of heavy users of cannabis.
“We really do not understand how these drugs might increase schizophrenia risk,” Dr. Stephen Kish, senior scientist and head of CAMH’s Human Brain Laboratory.
“Perhaps repeated use of methamphetamine and cannabis in some susceptible individuals can trigger latent schizophrenia by sensitising the brain to dopamine, a brain chemical thought to be associated with psychosis,” he added.
Dr. Kish also cautions that the findings do not apply to patients who take much lower and controlled doses of amphetamines or cannabis for medical purposes.
Since this is the first such study showing this potential link, the researchers emphasize that the results need to be confirmed in additional research involving long-term follow-up studies of methamphetamine users.
The finding has been published online at AJP in Advance, the advance edition of the American Journal of Psychiatry, the official journal of the American Psychiatric Association.