Substance-Related Disorders

Prescription Drugs and Alcohol Too Often Lethal Mix


By Pippa Wysong
The Medical Post, February 20, 1996

TORONTO - Prescription drugs and over-the-counter medications are playing a lead role in road accidents caused by impaired driving, according to a national study by researchers in Manitoba and British Columbia.

The study was started in 1987 by the drugs and driving committee of the Canadian Society of Forensic Science, said Wayne Jeffrey, head of the committee and head of toxicology at the RCMP forensic science laboratory in Vancouver.

The group collected all blood sample data of charged, impaired drivers from forensic science laboratories across the country, but focused on those who had low or no alcohol.

The samples were studied to see just which substances, aside from high alcohol levels, lead to impairment.

"These are people who were charged, were before the courts for impaired driving, whose blood alcohol samples were less than 100 mg/100 mL blood, or the police knew they were on a drug," Jeffrey said.

The national criterion for alcohol impairment is 80 mg/100 mL blood, though there is some variation between the provinces on when charges are laid.

In Ontario, people are not to operate a motor vehicle if their blood levels are above 50 mg/100 mL, but it becomes a criminal offence when levels are at 80 mg/100 mL, said a spokesperson from the Ontario Provincial Police.

Some provinces don't lay charges until the level is 100 mg/100 mL or more.

Between 1987 and 1994 the drugs and driving committee analysed 1,158 samples, including 776 from nonfatal impaired driving cases and 391 from fatal ones.

Close to half the impaired drivers, 590, had traces of benzodiazepines in their blood and 580 had signs of alcohol. Benzodiazepines are used in sleeping pills.

Cannabis was high on the list too, with metabolites of the drug being found in 550 of the cases.

However, cannabis is starting to be surpassed by benzodiazepines, narcotics, prescription tranquillizers and antidepressants, Jeffrey said.

Alcohol played a significant role too, even though the samples selected were below the legal limit.

Generally, studies estimate 40% to 50% of all fatal MVAs (motor vehicle accidents) have alcohol as a contributing factor, he said.

The rate is likely much higher when one includes small, normally nonimpairing levels of alcohol combined with other drugs.

"It's not the impairing effects of the benzodiazepines or the impairing effects of the alcohol but the combined effects of the two," he said.

A second study done by RCMP forensic scientists looked specifically for drugs and alcohol in blood samples taken from B.C. drivers who died within 24 hours of an MVA.

"We showed in 10% of cases drugs alone were found in impairing levels," Jeffrey said.

Across Canada, about 125,000 drivers per year are charged with impaired driving.

"If we go to our data saying 10% of those have drug involvement, we should be having 12,000 impaired driving charges just from drugs alone," he said.

In short, Jeffrey suggests "if you're tired, don't drive."

Many drugs and alcohol have a combined effect, said Dr. James Wright, associate professor of pharmacology, therapeutics and medicine at University of British Columbia.

A person who has even a small amount of a sedating drug, insufficient to cause impairment alone, can become impaired after drinking a small amount of alcohol, he said.

Doctors need to warn patients about these combined effects, said Dr. Wright, who is also clinical managing director of B.C.'s Therapeutics Initiative.


Copyright 1996 Maclean Hunter Publishing Limited
Reprinted with permission.

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