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Abstract
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Detecting impairment from cannabis is not as straightforward as detecting alcohol because of the complex nature of the drug and lack of conclusive research about the dose–effect of cannabis.
The widely used breathalyzer test can accurately detect alcohol impairment using a breath sample because the amount of alcohol in exhaled air closely relates to the amount of alcohol in the blood, says Dr. Robert Mann, a senior scientist at the Centre for Addiction and Mental Health (CAMH). “It correspondingly increases as alcohol is first absorbed into the blood and subsequently decreases as alcohol is metabolized and removed from the blood.”
But what makes breathalyzer screening viable is the substantial research showing that breath alcohol level is associated with impairment and the equally conclusive research that underpins the 0.08% blood alcohol concentration limit. That level of research isn’t yet available for cannabis, argues Dr. Bernard Le Foll, head of Translational Addiction Research Laboratory at CAMH.
Cannabis’ active ingredient, Delta-9-tetrahydrocannabinol (THC), is very lipophilic so it goes to areas in the body full of lipids, like fat or the brain, says Le Foll. “This means what we get in the blood is just an approximation of what may be in the brain.”
Although he says scientists have some idea of the relation between the blood and brain levels of THC, what is less clear is how this relates to the ability to drive. “The assumption is that it is parallel to alcohol — the more intoxicated a person, the more impairment. The reality is that we don’t have such solid evidence as with alcohol of this clear relationship.”
Although a number of epidemiologic studies do show that a person is more likely to be in a motor vehicle collision while driving after using cannabis than not, Mann agrees that we don’t know how this equates to the amount of THC consumed. “It’s difficult to establish a dose–effect relationship … researchers are doing work to establish something comparable to the per se level like we have for alcohol.”
Keywords: Cannabis impaired driving; DUID; Ethanol impaired driving
Language: en |