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How long should you wait after smoking pot before driving? 'No magic number,' says MADD

While the rough guideline is four to six hours, the effects will vary person to person and Mothers Against Drunk Driving says there's some level of personal responsibility.

Mothers Against Drunk Driving says the guidelines are rough and it comes down to 'personal responsibility'

CBC News ·
MADD's Eric Dumschat says young people are over-represented in crash fatalities. (Darryl Dyck/The Canadian Press)

It may be legal to smoke pot, but driving under the influence of pot could get you in trouble if you're considered impaired.

However, Mothers Against Drunk Driving (MADD) is worried that the rules are a little fuzzy.

Eric Dumschat, legal counsel for MADD, said the organization can only give guidelines as to how long people need to wait after consuming marijuana.

"At some level it does come down to personal responsibility. There's no magic number," said Dumschat. "You need to make that determination for yourself."

He said the organization has been using the range of four to six hours after consumption, but there's a lot of "personal variation" in terms of the degree and duration of impairment.

Roadside tests

Police will have a number of options for catching people driving under the influence of pot.

One is a standardized sobriety test officers have been using since 2008, said Dumschat. The newer one is a saliva test.

However, the technology is still relatively new and would not be as good as tests for blood alcohol, according to Dumschat, because there hasn't been as much research put into cannabis as there has been for alcohol.

The Dräger DrugTest 5000 comes with an 'analyzer' or reader, pictured here. It tests saliva for cocaine and THC, the main psychoactive agent in cannabis. (CBC)

"We suspect that in the coming years, these [tests] will become much more quick, much more accurate, much more cost-efficient," he said.

For now there have been concerns raised about whether low temperatures would affect the saliva test results or not.

Education needed

When it comes to preventing impaired drivers from getting behind the wheel in the first place, Dumschat said there needs to be "a lot more education" when it comes to pot.

"There's this persistent myth, especially among young people … [that] they drive better after they smoke pot," he said. "That is objectively false."

He referenced a McGill University study which showed young people who use cannabis and drive are at a greater risk of being in a collision even after five hours have passed.

"The science in this is clear," said Dumschat. "You can't drive if you are under the influence of drugs or alcohol."

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