Smoking or driving: should you choose?

Two Norwegian researchers have examined the probability of having a car accident after using cannabis and came to a surprising conclusion.

The study was published in the online journal Addiction and suggests that cannabis isn't as dangerous as you might think when it comes to handling a motorized vehicle.

The researchers had one objective in mind: to analyze the degree to which heavy cannabis use increases the likelihood of having an accident. To do this, they examined two separate studies.

The first study replicated two previously published meta-analyses, with the aim of correcting methodological flaws. It included a group of around 51,000 people, 23,000 of them from roadside checks, the rest being examples of cannabis intoxication, and a second sample of over 93,000 cases, 89,000 of them from roadside checks.

The second study was a revised meta-analysis involving 28 estimates from 21 observational studies. In all, the second study involved 240,000 people.

Effect of cannabis on driving

And what did they find?

Previous studies did not take into account known confounding factors (age, gender, etc.) which can distort results. By adjusting the previous results, the researchers determined that driving under the influence of cannabis increased the probability of an accident by a factor of 1.2 to 1.4. Simply put, there is a statistically significant increase in small-to-moderate proportions, in stark contrast to previous studies. Comparatively, alcohol increases the likelihood by 4.

This study is interesting for two reasons:

• it shows that cannabis does affect driving, albeit to a lesser degree than alcohol, but all the same
• it covers 30 years of statistics and 240,000 real-life cases, which is quite a change from studies where you take 18 guys and make them drink or smoke before taking them on a racetrack.

Cannabis in the blood and blood testing

The THC remains in the blood up to 2 days after the last cannabis intake. A study conducted in 2015 by the National Highway Traffic Safety Administration (the French equivalent of Prévention Routière) has drawn a surprising conclusion: the measurable presence of THC in the blood is not necessarily correlated with the effects of cannabis, unlike alcohol, whose blood level is indicative of its effects (reduced alertness, increased speed, etc.). The NHTSA does not mince its words: «At present, drug concentration levels cannot be reliably equated with a specific degree of driving impairment».

The explanation simply lies in the fact that drugs are eliminated in a different way to alcohol, and that they remain in our bodies longer, without always being active.

Legalization challenges

The countries or states that have legalized cannabis for therapeutic and/or recreational use are faced with a new challenge: regulating driving in the face of these new treatments.

In Europe, some drugs already warn of the dangers of driving, but are not penalized to the same extent as cannabis.

In France, of course, it is forbidden to use cannabis (for that matter, at all) and to drive afterwards. Analysis tools similar to breathalyzer tests already exist, with more or less convincing results.

Here again, research is needed to regulate the presence of THC at levels that will protect drivers and people on the road, while no longer condoning cannabis use in states or countries where it is legal.