Manitoba Public Insurance says it is extremely concerned about the number of drivers who are operating vehicles under the influence of drugs.
Based on cheek swab and breathalyzer samples collected voluntarily from drivers in September, MPI found 124 out of the 1,230 participants — one in 10 — were driving under the influence of a drug.
Prairie Research Associates was contracted by Manitoba Public Insurance to collect data for the roadside survey and the samples were destroyed after testing.
While 1,203 agreed to be tested, 503 declined to give a sample.
The results mean 10 per cent of drivers tested had drugs in their system, compared to only 2.4 per cent found to have alcohol in their system — a fact that surprised Ward Keith, communications vice-president with Manitoba Public Insurance.
"At 10 per cent, the prevalence of drugs in the tested drivers is significantly more common and extremely concerning," said Keith.
According to the September survey, 53 per cent of drivers testing positive for drugs had cannabis in their system, 31 per cent had cocaine, 12 per cent had opioids and two per cent tested positive for benzodiazepines (a class of drugs that includes Valium) and amphetamines (a common treatment for ADHD) or methamphetamines (commonly known as meth or crystal meth).
Of the drivers who tested positive, 22 per cent had taken more than one drug.
Car crash rates can increase when drugs are present, according to MPI.
The latest data on the subject, collected in 2013, shows about 40 per cent of drivers killed in road collisions who were tested had drugs in their system.
The study, Keith said, will help MPI develop a baseline for drug use ahead of changes to Canada's marijuana legislation expected this spring.
Manitoba Attorney General Heather Stefanson said the province is introducing a bill Thursday ahead of the new legislation that will address marijuana safety and health issues.
The bill will include changes to Manitoba's Highway Traffic Act, she said.
Drugged driving risks complex, says doctor
Dr. Andrea Furlan, a pain specialist with Toronto Rehab and former advisor to Health Canada on opioid prescription, urges caution before concluding all those driving with drugs in their system are impaired.
"It has to be individualized. We can't throw a blanket statement that everybody on these drugs are impaired," she said.
With opioids, for example, she said a patient with chronic pain may drive better on the drugs than in pain. It all depends whether the opioids a patient is taking are short-acting or long-acting and the patient's tolerance level.
"It's the same with people who have ADHD. A lot of adults, they have adult ADHD, and if they don't take their stimulant they drive bad," she said.
Furlan said marijuana can be a different story, since it causes impairment even for long-term users for the first three hours after smoking or vaporizing the plant.
Keith conceded the results of the survey don't necessarily tell MPI the level of drug impairment.
He noted, however, that the study did find 62 per cent of drivers who tested positive for marijuana had 10 nanograms or more in their system, which can be enough to impair driving.
Furlan said measuring nanograms can be a little misleading, as people metabolize cannabis differently.
Her team at Toronto Rehab is currently developing tests that can be conducted by clinicians in a doctor's office to determine the extent of impairment caused by prescription medication on a specific patient, she said.