It’s regulated or illegal in many jurisdictions, but that doesn’t stop many marijuana users from toking up. The 2009 Canadian Alcohol and Drug Use Survey found that 11.4 percent of Canadians (and 33 percent of Canadians aged 15 to 24) used marijuana at least once in the previous year. What adds to the danger is the number of people who drive while under the influence of cannabis – a problem researchers say is growing. National data collected in 2004 indicate that 4 percent of Canadian adults reported driving within one hour of consuming cannabis, up from 1.9 percent recorded in 1996-7. These results are reflected in other jurisdictions across the world. A roadside survey of 537 drivers in Scotland reported that 15 percent of respondents aged 17-39 years admitted to having consumed cannabis within 12 hours of driving a vehicle,and the European Monitoring Centre for Drugs and Drug Addiction found that between 0.3 percent and 7.4 percent of drivers tested positive for cannabis from roadside surveys in the United Kingdom, Denmark, the Netherlands, Norway, the United States, and Australia.
One of marijuana’s side effects is a marked distortion in the perception of time and space. For users who smoke and drive, the risk of collision is high. In fact, drivers who smoke marijuana before driving are nearly twice as likely to cause a car crash as sober drivers.
Experts from Dalhousie University in Halifax reviewed nine studies of more than 49,000 people involved in accidents and found drivers who had used marijuana within three hours of beginning to drive had nearly double the risk of causing a collision, especially those that were fatal.
Marijuana use was confirmed via blood tests or self-reporting.
The study was published in the BMJ journal on February 9. Access it here.