Canadian scientists also confirm previous research showing possible link
between cannabis dependence and schizophrenia
TORONTO, Nov. 8, 2011 /CNW/ - In the first worldwide study of its kind,
scientists from Toronto's Centre for Addiction and Mental Health (CAMH)
found evidence that heavy methamphetamine users might have a higher risk of developing schizophrenia. This finding 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.
The report will be published online on November 8, 2011, at AJP in Advance, the advance edition of The American Journal of Psychiatry, the official journal of the American Psychiatric Association.
Methamphetamine and other amphetamine-type stimulants are the second
most common type of illicit drug used worldwide.
"We found that people hospitalized 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," says 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.
To establish this association, the researchers examined California
hospital records of patients admitted between 1990 and 2000 with
diagnosis of dependence or abuse for several major abused drugs:
methamphetamine, cannabis, alcohol, cocaine or opioids. They also
included a control group of patients with appendicitis and no drug use.
The methamphetamine group had 42,412 cases, while cannabis had 23,335.
Records were excluded if patients were dependent on more than one drug
or had a diagnosis of schizophrenia or drug-induced psychosis during
their initial hospitalization. Readmission records within California
hospitals were analyzed for up to 10 years after the initial admission.
The researchers then identified patients who were readmitted with a
schizophrenia diagnosis in each drug group.
There has been a longstanding debate as to whether there is a connection
between methamphetamine use and schizophrenia. Many Japanese clinicians
have long believed that methamphetamine might cause a
schizophrenia-like illness, based on their observations of high rates
of psychosis among methamphetamine users admitted to psychiatric
hospitals. However, they lacked long-term follow-up studies of
methamphetamine users initially free of psychosis. In North America,
this link has mostly been discounted, as psychiatrists believed that
the psychosis was already present and undiagnosed in these
"We really do not understand how these drugs might increase
schizophrenia risk," says 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 sensitizing the brain to dopamine, a
brain chemical thought to be associated with psychosis." 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
"We hope that understanding the nature of the drug
addiction-schizophrenia relationship will help in developing better
therapies for both conditions," says Dr. Callaghan.
In an earlier study using California hospital records, the researchers
found evidence for a possible association between heavy methamphetamine use and Parkinson's disease
The Centre for Addiction and Mental Health (CAMH) is Canada's largest
mental health and addiction teaching hospital, as well as one of the
world's leading research centres in the area of addiction and mental
health. CAMH combines clinical care, research, education, policy
development and health promotion to help transform the lives of people
affected by mental health and addiction issues.
CAMH is fully affiliated with the University of Toronto, and is a Pan
American Health Organization/World Health Organization Collaborating
SOURCE Centre for Addiction and Mental Health
For further information:
Media Contact: Michael Torres, Media Relations, CAMH; 416-595-6015