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Drug of Abuse: Cannabis behind the Wheel

The debate has been going on for ages. Is cannabis safe while driving or – much like alcohol – does it affect response times and decision-making abilities? Has anybody ever had any issues with it while driving?

Well, in short, no, yes, and unfortunately, very much so. Consumption of cannabis influences the cognitive and psychomotor functions, essential when driving. These functions are closely related to our capacity of assessing immediate or potential danger and acting consequently. The THC in cannabis (tetrahydrocannabinol) is the main compound responsible for the psychological effects.

According to the European Center’s Cannabis and Driving report, cannabis is the illicit drug most often detected in drivers with fatal injuries in North America, Europe, and Oceania.

That being said, the variables here are many.  Usually, the tests conducted on injured or killed drivers happen several hours after the crash itself, therefore most of the time the THC level has already decreased. Blood HC-COOH results do not necessarily imply recent cannabis use. It can also be the result of regular use, and therefore unrelated to the accident at hand.

Moreover, not all cannabis consumption is equal. There are scientifically proven differences between the pharmacology of smoked and oral cannabis (European Center’s Cannabis and Driving report). While smoked cannabis leads to an immediate rush that decreases just as rapidly after smoking ceases, edibles may lead to a slower, but less predictable outcome. The effects peak at 2-3 hours, lasting for about 4-12 hours. At the same time, in the case of regular users THC accumulates in fatty tissue and keeps seeping back into the bloodstream potentially over long periods.


Currently, there are many jurisdictions where driving under the influence is outlawed. One way of detecting drivers under the influence of cannabis is roadside oral fluid testing. This is just one of the several methods of drug screening, which is preferred in many countries for the detection of DOA while driving.