Police should stop using urine samples to test for cannabis impairment, says defence lawyer

Aidan Cox · CBC News · Nov 07, 2022

Legal experts say cannabis-impaired driving enforcement is still fraught with pitfalls, including with the physical tests being used and the biological samples that are sent for testing. (File Photo/CBC)

The wrongful arrest of a woman falsely accused of driving while high shines a light on the pitfalls of policing cannabis-impaired driving, say legal experts.

Pam Staples-Wilkinson was arrested in March 2021 after getting in a car accident and later failing a standard field sobriety test conducted by a Fredericton police officer.

She ended up with a seven-day licence suspension and had an impaired driving charge hanging over her head for nine months — until the results of a urine sample proved she had no THC, the principal psychoactive compound of cannabis, in her system.

“I think it really highlights just how much power police have … and the pitfalls that can come not only with some of these tests but particularly when the police don’t do their job appropriately,” said Abby Deshman, director of the criminal justice program for the Canadian Civil Liberties Association.

Cannabis was legalized in October 2018, and since then, Ottawa has set aside millions of dollars to help police departments better enforce drug-impaired driving laws.

That help includes having more officers trained as drug recognition experts, who are certified to carry out a 12-step physical test, and to train more officers to perform the standard field sobriety test.

The federal government has also approved new roadside saliva-testing devices and has helped departments purchase them as a way to give quicker results for determining drug impairment.

‘These tests are not perfect’

The main tools police use to investigate drug-impaired driving are the standard field sobriety test, the drug recognition test, and biological samples taken from suspects.

However, “serious problems” remain with how officers conduct the two physical tests, said Kyla Lee, a Vancouver defence lawyer who focuses on driving offences.

“Particularly in cases involving collisions, individuals exhibit symptoms when performing the physical tests that police make you do, that are consistent with being in a collision, but also consistent with the consumption of a drug,” she said.

Balance problems, fumbling and slurred speech can all be the symptoms of shock and head injury suffered in a collision.

But they can also be interpreted by a police officer as impairment, giving them grounds to pursue charges, Lee said.

Staples-Wilkinson was first subjected to the standard field sobriety test, a three-step test that involves a walk and turn, a one-leg stand, and an eye test that involves following an object side to side.

When Const. Garret Fancy determined she failed it, he brought her to the police headquarters where she was subjected to an evaluation by Const. Dylan Howell, a drug recognition expert. He also deemed her to be impaired.

“It’s clear these tests are not perfect,” said Deshman.

“In this instance, you have someone who is obviously shaken because she is just in an accident and that can influence how people perform on the tests … and so they are one indicator that is not perfect, but needs to be viewed in the larger context of all the evidence.”

Problems with using urine samples

After the two physical tests, Staples-Wilkinson was then required to submit a urine sample, which was sent to a lab to test for the presence of Tetrahydrocannabinol, or THC, the compound in cannabis that causes impairment.

A negative result ultimately cleared her name, however, the use of urine samples by police is “a terrible way to ascertain whether somebody is impaired,” Lee said.

She said the first issue is it only shows the presence of THC, and not its concentration in the body, which would indicate how impaired a person might be.

Also, THC is fat-soluble, meaning it can be detected in urine in some cases months after it was smoked or eaten, Lee said.

“My recommendation would be for police to attempt to take blood samples instead of urine samples,” she said.

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