How do police test for cannabis-impairment?

How Do The Police Detect Marijuana

Police across Canada are trained to determine if a driver is under the influence of drugs. New cannabis laws allow police to use licensed drug screening devices to detect the recent presence of multiple drugs, including THC, cocaine, and methamphetamine.

Roadside Testing

If a police officer suspects a driver has drugs, alcohol, or both, the law requires an oral fluid sample after the stop or performs a standardized field breathalyzer test (SFST). can. These road tests cannot be used as a basis for prosecution or as evidence in criminal proceedings. Therefore, if a driver fails one of these two tests, there is the reason for officers to request an additional test at the police station.

1.  Standardized Field Sobriety Test (SFST)

The Standardized Field Breathalyzer Test (SFST) allows law enforcement officers to examine drivers’ eyes and subject them to a variety of tests, including:

  • walk in a straight line
  • stand up and turn or
  • to stand on one leg.

2.  Oral Fluid (saliva) Sample Testing

Reasonable suspicion: Police need to have a reasonable suspicion that a driver has drugs in his or her system in order to demand a driver take a roadside oral fluid screening test.

reasonable grounds to suspect could include a driver:

  • erratic driving in or out of lanes
  • follow other vehicles at unsafe distances
  • red eyes, muscle tremors, abnormal speech

The prohibited amounts of cannabis are:

  • Cannabis (THC): 2 nanograms (ng) to 5 ng THC per ml of blood (less serious crime). and more than 5 ng THC per ml of blood (more serious crime)
  • Combined alcohol and cannabis: 50 mg or more of alcohol per 100 ml of blood and 2.5 ng or more of THC per 1 ml of blood.

Testing equipment:

If police require an oral fluid sample, an approved drug screening device (ADSE) can be used to test the driver’s saliva. In Canada, oral fluid screening devices include both oral fluid collection sets and readers. This test detects the presence of certain drugs in oral fluids, including THC, the main toxic chemical in cannabis, and can determine if illegal amounts of cannabis, including THC, have been used recently. To see the categories of drugs other than cannabis, see Blood Drug Concentration Rules.

Testing at the police station

If the driver tests positive or fails the SFST, the driver may be arrested and taken to a police station for further examination. In police departments, officers trained as drug detection specialists perform drug detection evaluations (DREs) on drivers who they believe may be impaired by drugs other than alcohol or drugs in addition to alcohol may be implemented.

Drug Recognition Evaluation (DRE)

Breath Sample — Evidentiary Breath Test

Bodily Fluid Samples — For Alcohol and/or Drug Impairment



Priyanka Sharma

Priyanka Sharma is the content editor at with over 3 years of experience in journalism, Priyanka delivers fresh and accurate news on the cannabis industry to her readers. Her versatility as a writer and editor is showcased in her work. When she's not busy writing and editing, Priyanka can be found exploring new travel destinations and indulging in her love for food.

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