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How long to abstain from pot before hitting the road? Alberta researchers tackle the question

"'Could you consume a gram in an hour and then wait an hour and drive? We don't know the answer to that.'

Alberta researchers are exploring the the impact of marijuana in such areas as motor skills and attention span. (Associated Press)

Alberta researchers are trying to figure out how long you need to abstain from weed before getting behind the wheel.

The effects of alcohol on driving are easily measured but roadside testing for marijuana is still in the development phase.

With the federal government planning to legalize cannabis by July, researchers in Edmonton are aiming to study the effects of marijuana on users.

"So how much can you consume? Could you consume a gram in an hour and then wait an hour and drive? We don't know the answer to that," said Dr. Scot Purdon from the Department of Psychiatry at the University of Alberta.

Purdon is leading the study that will examine the effects of marijuana on users cognitive functions such as fine motor skills, attention span, distractibility and verbal learning.

He said he hopes they'll "be able to offer very clear guidance on how long you should be abstinent before the effects have cleared sufficient to operate a motor vehicle."

There is a lack of research on how THC, the active ingredient in marijuana, affects the brain, he said.

The effects of the drug can vary widely from person to person.

"We don't know is how long it takes to return to normal for you," said Purdon. "Do you have all of your memory capacity back, all your motor skills back within an hour or two hours of last use? Or does it take a week? Could it take even a month?"

He said the best evidence right now shows some verbal learning impairments associated with cannabis seem to persist for up to seven days after use.

"And that's for heavy use of a fairly intense product." he said.

Purdon said he and his co-investigators — Dr. Cameron Wild from the University of Alberta and Dr. Alexander Penney at MacEwan University — are also examining how the duration and frequency of use, and the age of the user, may contribute to impairment levels.

The study will focus on young adults who describe themselves as heavy users."...

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