Canada: Debate over THC limits for driving

Canadian scientists are currently discussing the THC limit for driving. Other countries have already taken such measures: in the USA, the limit is 5ng/ml in states where cannabis is legal, while in Switzerland the level is 1.5 ng/ml whereas in Australia and France, the slightest presence of THC prevents you from doing so, legally, to drive.

According to the Budding for Collins, THC levels in the blood can reach between 1 and 4 ng/ml after smoking a joint, depending on the dose and potency of the herb consumed.

Cannabis was the drug most frequently found in the blood tests of weekend drivers. In Canada, the rate of drivers taking THC was 8.6% in 2007 and reached 12.6% blood tests in 2014.

A 2016 survey by National Post, The results of a survey carried out by the French Ministry of Ecology and Sustainable Development, highlighted the impression of control that drivers feel when driving under the influence of cannabis. More than half of those surveyed claimed to be able to drive normally on cannabis, and some even said they could drive better on cannabis than sober.

Like alcohol, cannabis impairs the field of vision and reaction time. However, a few regular smokers seem to deviate from the rule.

There are many conflicting studies on the subject. In fact, the rate of THC in blood of road fatalities while the same THC level is measured in saliva of living pilots. However, all the studies agree on one common point: the peak dangerousness of cannabis behind the wheel is reached one hour after consumption. These same studies affirm that THC concentration in the blood rhymes with slower driving and greater concentration on the part of the driver.

A Norwegian study suggests that the ideal maximum permissible rate should be set at 2.2ng/L. On the other hand, this study also suggests lowering the permitted levels of alcohol and cannabis when the two are combined. The chances of accidents are multiplied by 15 when the two substances come together in the human body.

The zero-tolerance route does not seem to be recommended, as it can take up to 3 weeks for a regular smoker to evacuate the last THC molecules from his bloodstream.

Théo Caillart