CAMH study points to greatest harms of cannabis use in Canada

TORONTO, Feb. 4, 2015 /CNW/ - Among the major health risks linked to cannabis use, motor vehicle accidents and cannabis use disorders, including dependence, appear to affect the most Canadians.  These two factors are the main contributors to the cannabis-attributable disease burden in Canada, according to a new study from the Centre for Addiction and Mental Health (CAMH).

Lung cancer and psychosis, two other potential risks often associated with cannabis, affect fewer Canadians, although frequent cannabis use likely accounts for a number of lung cancer deaths each year, the researchers suggest.

The study was published online in the Journal of Public Health.

 "For the first time, we are providing rough estimates quantifying the four main categories of harms attributable to cannabis use," says lead author Dr. Benedikt Fischer, senior scientist in CAMH's Social and Epidemiological Research Department.  Cannabis is the most widely used illicit drug in Canada, but until now, the relative health harms it causes have usually been based on speculation, he says.

To estimate the actual extent of the impact of these four possible risks – motor vehicle accidents or injuries, cannabis use disorders, lung cancer and psychosis – the researchers took data from various sources to estimate the numbers of Canadians affected, in terms of health problems and death.

Motor vehicle accidents: The researchers estimated that four to 12 per cent of motor vehicle deaths or injuries occurred under the influence of cannabis. Based on motor vehicle accident statistics from 2010, this suggests that there were 89 to 267 fatalities, and 6,625 to 20,475 injuries in Canada that year related to cannabis use.

Cannabis use disorders: Cannabis abuse or dependence was estimated to affect 380,000 Canadians. This figure is based on a Statistics Canada survey, showing 1.3 per cent of Canadian adults aged 15 or older could be considered to be dependent on or to misuse cannabis in 2012. They estimate that between 76,000 and 95,000 people receive treatment each year for cannabis-related problems.

Lung cancer: Determining the link between cannabis use and lung cancer was difficult, given the overlap with tobacco smoking, as well as determining the amount and frequency of cannabis use and the fact that a diagnosis usually occurs years after use. However, after considering these factors in their calculations, the researchers estimated that one to two per cent of lung cancer deaths could be attributed to cannabis, corresponding to 130 to 280 deaths a year.

Psychosis: While recent reviews show regular cannabis users have a higher risk of psychosis, the association between cannabis use and schizophrenia is driven by a multitude of factors –including genetics – and may also be bi-directional, the researchers note. However, primarily in relation to cases where cannabis is used frequently, they estimated 106 to 186 cases of schizophrenia in Canada may be attributed to cannabis use. 

"These estimates are useful and intended to inform priority setting for public health interventions," says Dr. Fischer.  For instance, the findings suggest the need to improve ways to detect and deter cannabis-impaired diving, and expand treatment options for cannabis use disorders, the researchers note. 

The Centre for Addiction and Mental Health (CAMH) is Canada's largest mental health and addiction teaching hospital, and one of the world's leading research centres in its field. 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 Centre. For more information, please visit

SOURCE Centre for Addiction and Mental Health

For further information: Kate Richards, Media Relations, Centre for Addiction and Mental Health (CAMH), 416 535 8501 x36015,


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