top of page


Following the legalization of cannabis, many people have questions about the relationship between these Criminal Code changes and the law on impaired driving.

Some Background on THC Impairment and the Criminal Code

Although the use of cannabis is now legal, it is, like alcohol, a drug that alters reaction time, perception of time and space, and consequently, impairs people’s ability to safely operate a vehicle.

For quite some time, Criminal Code provisions have existed that quantify the amount of alcohol a person can have in their blood before being criminally charged for driving. However, until late December of 2018, drivers could only be convicted of impaired driving due to cannabis use if it could be showed using circumstantial evidence (swerving on the road, outward signs of intoxication, etc.) that the person was impaired. Now, however, like with alcohol, Criminal Code provisions have been introduced to establish the upper limit of allowable THC in one’s blood. A person found with between 2 nanograms (ng) and 5 ng of THC per millilitre of blood may be fined up to $1000. However, it is a much more serious offence to have 5 ng of THC or more per 100 ml of blood — at this level, a person may be fined a minimum of $1000, and may face prison time, as with a blood alcohol level above 80mg/100mL.

When You are First Pulled Over

When a police officer pulls you over, s/he should have reason to believe that you are driving while impaired by cannabis (or possibly other drugs, or alcohol). As above, this may be due to erratic driving, or due to a witness report of erratic driving. The police officer will further evaluate your speech, mannerisms, and behaviour, to evaluate whether s/he believes you are impaired. The police will likely look carefully at your eyes with a flashlight, ask you to walk, turn around, and/or stand on one leg. This is called a Standardized Field in Sobriety Test (SFST). You do not have the right to refuse to do this - in fact, failing to comply with the request to perform these tests is itself a criminal offence. While you are not required to answer the police’s questions, this will likely prompt the police to require an SFST, and likely, further testing as described below.

Drug Recognition Evaluation

If your SFST leads the police officer to believe that you are impaired by marijuana, then the officer will typically want to perform a Drug Recognition Evaluation (DRE). This test is more thorough and will help to conclude whether the amount of THC in your body is sufficient to impair your driving ability. This is a 12-part test — police officers are given training to conduct these tests, which include a comprehensive variety of techniques to determine impairment, including inspecting the eyes, and various other forms of physical testing (sometimes including a urine sample).

Note that, prior to the new Criminal Code provisions coming into force at the end of 2018 (i.e. that deem an individual to be impaired at 5 ng of THC per 100 mL), witness evidence, police observations at roadside, and a DRE would be the best evidence available to support impairment. Blood tests were not typically conducted when the use of marijuana was suspected. For example, in the recent appeal decision R v. Scarlett 2019 ONSC 796, the judge reviews the basis on which the defendant was convicted. This included erratic driving, as witnessed by a passenger in a vehicle on the road, and who had called 911; the police officer’s observations that the defendant’s eyes were bloodshot and glassy, and the fact that there was marijuana present in the defendant’s urine. The judge found the evidence of erratic driving to be the most compelling evidence. Similarly, in another recent decision R. v. Avery-Quick 2019 ONCJ 36, the accused was witnessed driving erratically, and was then apprehended by police. Although he smelled of alcohol, when a breathalyzer was taken, the police officer at the scene did not believe that the results were reflective of the accused’s true level of impairment. As such, he was subject to a DRE (like in the Scarlett decision, above), and as part of this, produced a urine sample that was shown to contain a variety of prescription and other drugs. Again, he was found guilty in all of the circumstances.

Blood Testing

As part of a DRE, and if there is reason to do so, the officer conducting the testing may now determine whether to take a formal blood test to determine the actual level of THC in a suspect’s blood. It is this test that will typically be used to support a finding of an objective level of impairment sufficient to charge you under the new Criminal Code provisions that make it an offence to drive with a blood THC level above 5 ng/100 ml.

Saliva Screening Devices

Across Canada, some police services have begun to implement the use of a roadside saliva test using a federally approved device called the Drager Drug Test 5000, much like a roadside breathalyzer, but for THC and cocaine. This can be used as an interim test to determine whether to take a blood sample. However, there has been some controversy surrounding this piece of equipment, as its degree of reliability is still uncertain. One U.S. study showed that the device is 98.7 percent accurate with regard to THC and 99.1 percent accurate in relation to cocaine.

To date, several people charged with impaired driving in Canada have been charged in part due to the results of tests conducted using this device. Many of these people will make legal arguments to challenge their convictions, or to defend their case, on the basis of the device’s unreliability - however, the device results would not generally be used to charge a person with impaired driving, only to determine whether to subject them to further testing. Some may attempt to make arguments relating to improper process or procedure, however.

Contact David Wilcox, DUI Lawyer & Drug Lawyer in Barrie

The criminal defence lawyer at our firm can help, no matter what you circumstances are. If you have been charged with impaired driving and want to ensure that you protect your rights and explore all possible defences, call our Barrie criminal lawyers. For a free 30 minute initial consultation, call 1-855-721-6642.


bottom of page