The most troubling issue for many Canadians, regarding the legalization of marijuana on October 17, is whether heightened cannabis use will lead to an increase in motor vehicle accidents caused by drivers who are high.
Provincial and municipal police forces in Ontario are attempting to address this concern through a number of initiatives, including training many more officers in drug recognition and standard field sobriety testing. Further, under Bill C-46, changes to impaired-driving laws were enacted in Canada’s Criminal Code. The new regulations set blood drug concentrations for THC (tetrahydrocannabinol) which will result in penalties and/or criminal charges. THC is the active ingredient in marijuana and persons should not have any THC in their blood when driving. The severity of charges will depend on how much THC is in a driver’s blood (as measured in nanograms per millilitre: ng/ml) within 2 hours of driving.
Does pot consumption reduce driving ability?
On radio programs leading up to legalization, many of us have heard regular pot smokers admitting that they often drove after smoking pot but did not believe it effected their ability to drive. There is, in fact, some inconsistency in findings for studies on driving impairment due to cannabis and some studies suggest that marijuana users tend to have a higher awareness that they are impaired which allows them to more often compensate effectively while driving. However, the general conclusion, based on many studies, is that cannabis consumption does, in fact, impair some driving-related skills, although the effects of pot seem to vary more between persons compared with the effects of alcohol. The variation in effect for pot smokers has been attributed to differences in tolerance, smoking technique and differences in the absorption of THC. Nevertheless, it’s been concluded that recent smoking and/or blood THC concentrations higher than 2 nanograms/millilitre result in significant driving impairment, particularly among occasional smokers.
Further, the Government of Canada reports that 40 per cent of drivers killed in car crashes test positive for drugs (with includes marijuana, cocaine and other drugs). This number now exceeds the 33 per cent who were killed and tested positive for alcohol. But, combined alcohol and marijuana use has been identified as the most dangerous combination for drivers, as it results in a greater level of impairment than under the influence of one alone.
Regardless whether a driver subjectively believes that pot will negatively affect their ability to drive, what’s more to the point is that it’s illegal to drive in Canada while under the influence of either cannabis or alcohol. This means, of course, that a driver can face criminal charges if pulled over while driving high or if they cause an accident and injury to another person. And, in the latter case, a driver can be held liable for any losses sustained by the accident victim(s).
On the question of ‘how long can a person safely drive after consuming marijuana’, there are no clear or definitive answers. When smoking pot, it’s been suggested that a person should wait at least 2 hours after 1 hit, but perhaps as much as 4 to 6 hours, depending on the THC and frequency of consumption. On the other hand, when an edible is consumed, traces of THC can be in the blood much longer, for as much as 12 hours or more, since it takes longer for the body to absorb the active ingredient. And, beverage companies, including beer and pop manufacturers, are reportedly looking into creating products containing THC or CBD (the non-psychoactive weed components), and no one currently knows how long the effects of a liquid cannabis may impact driving ability. Given the many unknowns, when considering how long to wait, it’s best to err on the side of caution and don’t drive after consuming pot - choose another form of transportation entirely.
“The Effect of Cannabis compared with Alcohol on Driving”, www.ncbi.nlm.nih.gov/pmc/articles/PMC2722956/
“Cannabis Effects on Driving Skills” (2013), http://clinchem.aaccjnls.org/content/59/3/478.short