Marijuana Use and Roadside Testing for Drug-Impaired Driving

2018.09 cannabis

Recreational marijuana (cannabis) use will be legal in Canada as of October 17, 2018. Whether you are a driver, or plan to use marijuana recreationally following that date, there are several law changes which have been made to protect the safety of everyone on the road. 

Written by Jordan D. Assaraf, Personal Injury Lawyer

Changes in law and what it means for drivers.

Before the official legalization of cannabis, the federal government has updated its Criminal Code provisions relating to impaired driving. On June 21, 2018, three new offences were created to address prohibited concentrations of drugs in the bloodstream within two hours of driving. If a person registers more than two nanograms of THC (tetrahydrocannabinol) - the main psychoactive element in cannabis - but less than five nanograms per millilitre of blood within two hours of driving, they will face a summary conviction offence. Other changes include:

  • five or more nanograms of THC per millilitre of blood
  • more than 50 milligrams of alcohol per 100 millilitres of blood and 2.5 nanograms or more of THC per millilitre of blood

If a driver is found to have any of these blood-alcohol and blood-THC levels while operating a motor vehicle, they will be subject to a hybrid offence. These offences also apply to any detectable levels of other impairing drugs including cocaine, methamphetamines, lysergic acid diethylamide (LSD) and others.

How is THC measured in blood tests?

Police can now use saliva tests to detect THC and measure the amount residing in blood. These tests are similar to breathalyzers, which measure alcohol levels in blood. Unlike alcohol measurements, THC levels are measured through blood in nanograms. A nanogram measures out to one billionth of a gram, and in blood tests for THC nanograms are measured per millilitre of blood. That leaves an incredibly small threshold for active THC levels in the bloodstream. For those who frequently ingest THC, their nanogram per millilitre level may rest at an active 5 nanograms per millilitre of blood, even if they have not ingested THC in the last few hours, or even days. In light of these new law changes, those who frequently ingest THC may be at risk of impaired driving following a THC blood test, even without recent cannabis ingestion. Unlike alcohol, the metabolism of THC is not predictable on a person to person basis. For that reason, there is no way to predict an individual's THC level 2 hours after consumption. To understand how quickly your body metabolizes THC, consult your specialist or doctor and refrain from driving while under the influence of any substance. By law, drivers are not permitted to operate any motor vehicle while impaired by any drug (prescription or non-prescription).

Related concerns following these updates

In light of these recent law changes, there are several concerns surfacing which may affect the ability to test drivers who are suspected to be under the influence. Among these concerns are:

  • a recently approved roadside saliva test for THC and other drug compounds may not be very reliable in cold climates like Canada
  • medical marijuana users who have developed a higher tolerance for THC without showing signs of impairment may be prevented from driving due to high concentrations of THC in their blood (please refer to the section above which addresses the measurement of THC in blood tests for clarity).

Be smart and drive safely on the roads

It will be important to be especially vigilant on the roads as the legalization of marijuana occurs. You may not know if a fellow driver on the road is under the influence. Keep a safe distance from cars in front of you, and if you suspect someone is driving under the influence of alcohol or drugs, safely pull over to the side of the road before calling 911. Use extra care at night and reduce speeds when necessary. NEVER ingest drugs or alcohol and drive. Recreational marijuana users must act responsibly. Use designated drivers, call a friend for a ride, use public transport, call a taxi or stay where you are. It is your responsibility to drive safely and operate any vehicle sober, and fully without impairment. When it comes to the safety of those on the road, no excuse is good enough to validate driving while under the influence.


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