How much weed can you smoke just before getting behind the wheel? Simply put, none

Clare Clancy

Hundreds of people attended the Edmonton 420 marijuana rally held at the Alberta legislature grounds in Edmonton on April 20, 2017. Larry Wong / Postmedia, file

Taking one toke of a joint is enough to lead to a traffic fine under rules rolled out ahead of the legalization of cannabis in Canada next year.

Drivers who smoke weed and don’t want to get caught legally impaired would need to wait at least several hours before getting behind the wheel, said Doug Beirness, senior research associate at the Canadian Centre on Substance Use and Addiction (CCSA).

“There really is no amount of cannabis you can smoke and stay under a level of two (nanograms per millilitre),” he said in an interview from Ottawa.

The Alberta NDP introduced Bill 29 Tuesday to update the provincial Traffic Safety Act in response to federal legislation and pending changes to the Criminal Code of Canada. Use of recreational pot will be legal July 1.

Under Bill C-46, impaired drivers face a maximum $1,000 fine if their blood tests positive for two to five nanograms per millilitre of tetrahydrocannabinol (THC), the main psychoactive compound in cannabis.

Those penalties increase as THC levels rise — drivers face a minimum $1,000 fine for blood tests showing more than five ng/mL for a first-time offence.

Second offences and beyond are subject to harsher penalties, such as jail time. That goes for combined alcohol-cannabis use of 2.5 ng/mL of THC with a blood-alcohol level of .05 as well.

Zero tolerance

The rules include zero tolerance for new drivers under Alberta’s graduated licensing program.
A CCSA study released earlier this year found that in 2012 there were 75 fatalities across Canada due to cannabis use while driving. Add to that more than 4,400 injuries and close to 7,800 victims of property damage.

Edmonton-McClung NDP MLA Lorne Dach — who supported Bill 29 — told the legislative assembly on Thursday about the death of his younger brother Kevin Dach due to impaired driving.

On Grey Cup day in 1977, his 17-year-old brother was killed by a drunk driver, along with two others in the same car.

“All were students at Lakeland College, full of promise, and every family affected horribly by it,” he said during a committee of the whole, recorded in Hansard.

“I seldom will have a drink if I’m going to drive, and I do ask myself whenever I’m at a function — how many joints or drinks would I like my airline pilot to have before they get into the cockpit?”

Dach — who said that’s the question that needs to be asked when debating impaired driving legislation — touted a zero-tolerance policy in the long-term.

“In the meantime implementing the legislation now will act as a deterrent and save lives even as we seek a reliable test method,” he said.

‘Four hours … Eight would be better’

Transportation Minister Brian Mason said drivers who use cannabis should wait at least 24 hours before heading out on the road. “The cannabis enforcement mirrors what we do with alcohol.”

But using alcohol regulations as a framework for cannabis could be problematic, Beirness suggested.
A blood-alcohol content of .08 or higher can lead to a criminal charge. That number — 80 milligrams of alcohol in 100 millilitres of blood —  amounts to around four drinks or more for most people, he said.

“We could easily say ‘You could have a couple (of drinks) and you’re probably under the limit’,” Beirness said. “You can’t say to someone, ‘You can have no more than a joint’.”

Until relatively recently, THC content in cannabis was around five per cent, he said. Now that’s closer to 20 per cent. “It’s gone up dramatically.”

Potency is even higher for products including cannabis oil, shatter, wax and butter, which can have 90 per cent THC content.

So, what is the minimum amount of time someone should wait to drive after consuming cannabis?
“I would say at the very, very minimum four hours and that probably isn’t good enough … eight would be better,” Beirness said. “Then again, it depends on how much you smoked, what you smoked or how you used it, and how often you use it.”

Although there aren’t easily-determined thresholds for cannabis use and driving, he said the regulations act as a deterrent — “there’s a value in having a limit.”

Testing for THC

The federal government has said saliva-based screening is under development, which would give police a roadside tool to screen drivers under suspicion of using drugs.

But there’s no test that determines an individual’s impairment, and even waiting 24 hours doesn’t guarantee a negative THC blood test.

A chronic cannabis user who smokes three or more blunts a day could test positive for THC two weeks after quitting, Beirness said.

“You accumulate this level of THC in your fat cells which is slowly being released in your blood,” he said.

“Cannabis impairments are highly variable.”