When the Cannabis Act comes into effect on October 17, it brings with it a slew of changes to laws regarding possession, distribution, and the selling of cannabis in Canada. 

Some laws, however, will not be changing. Driving under the influence of cannabis is and will remain illegal after October 17, and rightfully so: several statistics show that driving under the influence of cannabis significantly increases the risk of vehicle crashes, especially fatal ones.

Driving high is not uncommon either. A Health Canada survey from 2017 reported that 39 per cent of individuals who use cannabis had driven a vehicle two hours after smoking marijuana. 

This summer, Parliament passed Bill C-45, which clarified the legal amount of tetrahydrocannabinol (THC) — the molecule responsible for getting you high — allowed in the blood while driving. Having two to five nanograms of THC per millilitre of blood constitutes a summary offence. Having more than five nanograms could get you jail time. Still, the procedure for determining drug impairment on the road remains hazy.

Current testing procedures

Law enforcement in Canada currently monitors drug impairment on the road in the same way it does alcohol. If a police officer suspects that you are driving impaired — whether from observing abnormal driving behaviour or simply smelling drugs or alcohol on you during a traffic stop — they can have you take a Standard Field Sobriety Test (SFST). This test, much like an acrobatics audition, will test your balance and coordination. 

You might also undergo a drug recognition evaluation (DRE). Here, if alcohol impairment is suspected, a breathalyzer is used. If not, you can be physically examined for evidence of drug use like having your pupil size measured. Lastly, a toxicological sample, like urine, saliva, or blood, is sent to a forensic lab for examination.

One of the most glaring differences between testing for alcohol impairment versus cannabis impairment is that the former is rapid — alcohol impairment can be determined on the roadside — but impairment by any other drug, including cannabis, is determined after the toxicological sample has been examined. 

The absence of a rapid roadside drug test is concerning, considering the prevalence of drug-related car crashes and the subjectivity of the SFST and DRE. According to Mothers Against Drunk Driving, in 2014, there were twice as many fatal vehicle crashes involving drugs than crashes involving alcohol. Cannabis accounted for 45 per cent of all these drug cases. 

Take your breath away

Several companies are developing cannabis breathalyzer technology, including SannTek, which is based in Kitchener.

SannTek’s breathalyzer is currently being marketed to industries in which drug impairment poses a safety issue, like mining, transportation, and construction, with hopes that law enforcement will follow. Noah Debrincat, CEO and co-founder of SannTek, wrote that the advantage of using breath as a testing medium is that it can only measure recent drug use.

“The advantage… is that it actually correlates to when a user would experience the acute impairing effects of cannabis. Contrast this with the use of something like urine tests, where a person could use recreational cannabis safely on Saturday night, and on Monday would fail a urine test requested by an employer, even though they are not impaired,” wrote Debrincat.

Vivienne Luk, an assistant professor at UTM and forensic toxicologist, says that cannabis breathalyzers have limitations. “There is limited research on the relationship between THC concentration in the breath and its relation with other bodily fluids, like blood,” wrote Luk.

Luk, who regularly testifies in court as an expert witness, says that the functionality of drug screening devices is often questioned in court. “Would smoking, using breath mints, or chewing gum interfere with the functionality of the device? These are questions that are often asked in court cases involving the alcohol screening devices, so I am certain THC ‘breathalyzers’ will also be subjected to similar questioning.”

Saliva sensors have been recently approved by the federal government for roadside cannabis testing, and Toronto police have already completed pilot programs with them. The saliva sensors have similar limitations to breathalyzers: drug concentrations in your saliva can be a diluted representation of what is actually in your blood, potentially leading to underestimations and false negatives.

Other bodily fluids

If breath and saliva are potentially out, what bodily fluid is left? U of T professor Andreas Mandelis from the Department of Mechanical and Industrial Engineering says that interstitial fluid is the answer. 

Mandelis, whose lab is developing a non-invasive cannabis sensor, says interstitial fluid, the fluid surrounding all the cells in your body, carries an accurate ‘memory’ of substances that are in your blood. For THC, it only takes several minutes after it reaches your bloodstream for it to reach the interstitial fluid.

Mandelis and his team measure interstitial fluid THC levels using technology based on infrared radiation. To understand how this works, bear with me for a quick refresher on high school physics.

All materials and objects absorb and emit infrared radiation. This includes our own bodies: humans are constantly emitting infrared radiation, which, unlike light, is invisible to the naked eye. Instead, it is perceived as heat. 

“It’s like in the movie Predator, where the predator couldn’t see in the visible light range but could see in the infrared range,” said Mandelis. “That’s why Arnold Schwarzenegger put mud on his face and body so that he would not be detected… It’s exactly those thermal photons we are looking at.”

What is not explained in Predator is that sometimes the wavelength in which a material — or even a molecule — emits radiation is distinct enough that it can be used to identify that material or molecule. “At that wavelength, at that peak, that only belongs to one molecule,” said Mandelis. This means that if the titular antagonist from Predator had a more sophisticated sensor, it could have identified Schwarzenegger as Schwarzenegger, not just as ‘human.’ 

Thankfully, Mandelis does have a more sophisticated sensor. In order to obtain that specific signature from THC, Mandelis’ sensor directs a laser at your fingertip. Once the laser penetrates to the interstitial fluid — just several microns below the surface of your skin — any THC molecules present will absorb the laser light and re-emit it as infrared radiation at a frequency that is specific to THC. 

“Once the heat is emitted, I have an infrared sensor that can monitor that,” said Mandelis.

Here lies another benefit of testing interstitial fluid to monitor THC concentrations: it is non-invasive. In other words, you can measure the level of THC in your body without actually pricking, poking, or taking any sort of tissue or fluid sample.

Moving forward

Be it a breathalyzer, saliva sensor, or infrared detector, we may have some type of roadside cannabis sensor soon. While technological advancement is important, we cannot forget the human and physiological factors. Luk explains that the levels of THC in your body may be influenced by the user profile. Whether you are an occasional or chronic smoker and whether you smoke or ingest cannabis can influence how much THC ends up in blood, how quickly, and for how long.

For now, Luk suggests that we do not abandon our current roadside methods. “It is important to keep in mind that these devices are designed for screening purposes only, meaning a positive result is a tentative finding and confirmation with a more accurate technique is required.”