Article by Wency Leung, Globe and Mail
Police who suspect people are driving under the influence of cannabis may ask them to perform a roadside sobriety test, or have them give blood or saliva samples. But even policy-makers recognize these methods, which work reasonably well for alcohol, are unreliable when applied to cannabis.
Now in labs across North America, the race is on to find a way to objectively measure cannabis-induced impairment. Researchers are trying to develop a tool for cannabis, akin to the Breathalyzer test – whether it is by identifying some yet-unknown compound in bodily fluids, tracking brain signals, or measuring how well people perform on tests taken on a mobile digital device.
The current system is imperfect because while drug tests can measure how much cannabis someone has in their system, they cannot tell how the drug is affecting that person’s ability to function, since impairment depends on many factors, says Dr. Ryan Vandrey, an associate professor of psychiatry and behavioural sciences at Johns Hopkins University School of Medicine in Baltimore. People have varying tolerance of the drug and different modes of consumption can produce different results: When given the same amount of cannabis, for example, long-time users tend to be less impaired than first-time users, and people tend to be more impaired when they vapourize the drug than when they smoke it.
“There’s no cut-off value for THC [the main psychoactive compound in cannabis] in blood or a metabolite in saliva or urine that can reliably determine whether someone is acutely impaired,” Dr. Vandrey says. “You can miss it on both sides: You can have people who are not impaired test positive, and you can have people who are impaired test negative.”
So Dr. Vandrey and his collaborators are now studying ways of measuring how high people are, which includes searching for alternative markers in bodily fluids that may more reliably determine impairment. Whether these markers may be other components from the cannabis plant, or some kind of protein that changes in blood or urine, the researchers do not yet know. They are analyzing biological specimens, and comparing them with data from behavioural tests of research participants to see if any patterns arise.