The Road Safety Monitor, a national telephone survey conducted each year involving Canadian drivers indicates that drug impaired driving is seen as second only to alcohol
impaired driving as a serious issue and that illicit drugs are seen as a more serious
problem than prescription or over the counter drugs1. Overall, 17.7%, or 3.7 million
Canadian drivers report driving within two hours of using illicit, prescription or over the
Collisions remain a major cause of death and injury in Canada, and concerns about the
role of cannabis in road safety in this country date back many years. Much less is known
about the impact of cannabis on road safety than the impact of alcohol, in part because of
the much greater difficulty involved in measuring the presence and amount of
cannabinoids compared to alcohol. However, there is renewed interest in this issue
stimulated in part by proposed legislative changes on the part of the Government of
Canada to reduce substantially the penalties for possession of small amounts of cannabis.
The purpose of this paper is to provide an overview of available research and evidence on
the potential impact of cannabis on road safety in Canada focusing on two areas: 1)
research on the prevalence of cannabis use in Canada; and 2) research on the prevalence
of driving after cannabis use in Canada.
Prevalence of Cannabis Use in Canada
Little information is available on the prevalence of cannabis use in Canada prior to the
1960s. However, in that decade, cannabis use increased substantially. While a variety of
possible sources of information on cannabis in the Canadian population have been used
over the years, including such measures as amounts of the drug seized by police and the
number of individuals prosecuted by the courts for cannabis offences, the most direct and
the most accurate measures of the prevalence of cannabis use are those derived from
surveys. Although cannabis is an illegal drug and there are concerns that survey
responses may be influenced by its legal status, research demonstrates that respondents
to anonymous surveys, where there are no adverse consequences involved, generally
provide valid responses.
Smart and Fejer presented one of the very first estimates of the prevalence of cannabis
use in a Canadian population, based on a survey of a representative sample of residents
of Toronto conducted in 1971. They found that 12.2% of males and 5.5% of females had
used cannabis at least once in the preceding year. The prevalence of use differed
substantially by age group and gender. Among males, 41.5% of those aged 18-25, 20.8%
of those aged 26-30, and 1.8% of those aged 31 and over had used cannabis in the
preceding year. Among females, 20.0% of those aged 18-25, 6.3% of those aged 26-30,
and 1.8% of those aged 31 and over had used cannabis in the previous year. These data
clearly demonstrate that, by the end of the 1960’s, cannabis use had become very
common among young people. Ogborne and Smart reported on cannabis use in the
general population of Canada aged 15 and over based on the National Alcohol and Other
Drugs Survey conducted in 1994. This survey was the largest representative survey with
information on cannabis use ever made in Canada, with a sample size of 12,155. Use of
cannabis at that time was relatively uncommon, but not rare. Only 7.3% of respondents
reported using cannabis in the preceding year, and 2.0% reported using it as often as once per week. However, nearly a third (29%) reported that they had used cannabis at least once in their lives. Substantial regional differences were observed, with the proportion reporting use
at least once in the past year ranging from a low of 4.9% in Ontario to a high of 11.4% in
The data provide a valuable perspective on the use of cannabis across Canada,
unfortunately there is little information on other important issues, such as change in rates
of use over time. However, in Ontario a series of surveys has been conducted over the
past 20 years that allow a picture of current use and changes in use over time in that part
of the country.
The Use of Cannabis in Ontario
Repeated cross-sectional surveys conducted in Ontario by the Centre for Addiction and
Mental Health provide the most comprehensive picture of the use of cannabis and other
drugs use in Canada. These surveys have been conducted among the student population
and adult population since the late 1970s.
A summary of recent data on the use of cannabis and other drugs (any
use in the past year) among students in grades 7 and 126, and among adults aged 18-29
(young adults), 40-49 (the middle-aged) and 65 and over (seniors). shows cannabis is the most
widely used illicit substance, with nearly half of grade 12 students reporting cannabis use
at least once in the past year. It is worth noting that by grade 12 most students will have
reached the age when they will be eligible to drive. Use of cannabis drops with increasing
age, however, and is used by less than 2% of seniors. Use of other illicit drugs is much
less common than the use of cannabis, with highest levels occurring for Hallucinogens and
Ecstasy among grade 12 students. Not surprisingly, alcohol is the most commonly used
substance. While cannabis is used by a smaller proportion of students than alcohol; it is still used
by a substantial minority of students. There have been important changes in the use of
cannabis over time. The general trend appears to have been one of reduced use of cannabis
and alcohol from the late 1970’s to the early 1990’s. The proportion reporting use of cannabis declined from a peak of 31.7% in 1979 to 11.7% in 1991. However, since the mid-1990’s self-reported use
of both substances has increased, with 28.6% reporting cannabis use in 2001.
Prevalence of Cannabis Use and Driving in Canada:
Survey data on the prevalence of driving under the influence of cannabis are available. In
the first reported data from the general population in Canada, the prevalence of driving after
use of cannabis at least once in the preceding 12 months. The
survey included 9943 persons aged 16-69, obtained through random digit dialling.
The prevalence of DUIC varied with age, while the prevalence of DUIC was relatively low,
it was higher in younger age groups. DUIC was significantly associated with a variety of other risk behaviours, such as driving after drinking, use of illicit drugs other than cannabis, and collision
Information on the incidence of DUIC in a representative sample of the Ontario adult
population surveyed in 1996/97.
Among all drivers, 1.9% reported DUIC in the previous 12 months. Several factors influenced the likelihood of reported DUIC, including gender, age, marital status and education level. DUIC was most
frequently seen in younger age groups, with 9.3% of the youngest age group (18-19)
reporting the behaviour. DUIC was more common among men (3.0%) than women
(0.8%), more common among those never married (4.7%) than among those married
(0.9%) or previously married (2.1%). It was also least common among those with a
university degree. Among cannabis users, DUIC appeared to be a relatively common
behaviour; 22.8% reported DUIC, and the probability of the behaviour was significantly
influenced by gender and education level As well, DUIC and drinking-driving were strongly
related in this sample.
Prevalence of DUIC by Age among Cannabis Users in Ontario, 1996-97
Data derived from Walsh and Mann8.
The observation that DUIC was more common among younger respondents was recently
extended . Among students with a drivers licence in grades 10-13, 19.3% reported driving
within one hour of using cannabis at least once in the preceding year; this proportion was higher than the
proportion that reported driving within an hour of two or more drinks (15.0%). Males were
significantly more likely than females to report DUIC (23.8% versus 13.5%). DUIC was
more frequently reported than driving after drinking .
Prevalence of riding with a drinking driver, drinking driving, and DUIC by Gender
among Ontario students, 2001
Among respondents, 5.1% reported using marijuana, and 1.5% reported DUIC at least
once in the preceding 12 months. These authors also noted that males and respondents
under 30 were most likely to report DUIC, and also that there was a strong relationship
between DUIC and driving after drinking. Recently, the first report on trends over time in
cannabis use and driving in Canada appeared.
The proportions of Ontario adults reporting DUIC in a representative sample
of the Ontario population surveyed in 2002
A trend for an increase over time was observed, with the proportion of adult drivers reporting DUIC increasing from 1.9% in 1996/97 to 2.7% in 2002. The authors note, however, that this increase is not statistically significant and recommend further monitoring of this trend.
The data presented here indicate that cannabis use is relatively common in Canada,
particularly among young people. The prevalence of use appears to have increased
substantially in the 1960s and ‘70s, while since then some fluctuations have occurred.
Driving after cannabis use is less common, but among cannabis users it does appear to
occur with some frequency. In particular, young cannabis users appear more likely to
report DUIC. Among high school students, DUIC appears to occur as frequently, or more
frequently, than driving after drinking. These data provide grounds for concern about this
behaviour, particularly among younger drivers. Further research on the prevalence of
DUIC in Canada, including differences between provinces, is needed.
Source: CAMH Population Studies eBulletin, May/June 2003 No.20