Even if marijuana gets the federal government's blessing in the form of legalization, employers, especially those in the construction industry, should remain more strict, warns a health manager with a drug testing company.

"Marijuana and dangerous activities, safety-sensitive duties, can't mix," says Dan Demers, who works at CannAmm Occupational Testing Services.

"The issue is, the use the night before work actually affects performance the next morning."

Construction and the downside of drugs

Speaking at this week's 2017 Newfoundland and Labrador Construction Safety Association's annual conference in St. John's, Demers highlighted specific issues when it comes to marijuana use.

He said reaction time and depth perception can be affected if someone uses marijuana the night before.

"If you're working at heights in the construction industry, your ability, for instance, to take into account somebody besides you, their facial expression changed because something's falling, the part of the brain that's responsible for recognizing facial expression gets impeded for over 12 hours," Demers told CBC's St. John's Morning Show.

A construction worker on the Alt Hotel project in downtown St. John's. Demers said working at heights can be especially dangerous, even if drugs were used the night before work. (Gary Locke/CBC)

He said it isn't just weed or other illegal drugs that cause impairment, noting "there are many prescriptions that are not safe in many dangerous environments."

Demers said there needs to be clarification on what he calls a common misperception about medical marijuana.

"Marijuana is not a prescription. It's an authorization, it's a legal access to posses, it's much different than a prescription."

What's old is new again

With marijuana legalization looming, drugs in the workplace "is an old issue, but yet a new issue," said Demers.

"It's going to become much easier to access and there's going to be less cultural stigma towards it ... and the consequence is we're going to see it more frequently on our roadways, more frequently in our work sites," he said.

"And the ones that are dangerous, that's going to have some consequences."

Demers said with the legalization of marijuana closer than ever, employers need to consider their options. (Associated Press)

He said ultimately, the responsibility lies with the employer.

"[If] they have their messaging correct and they're willing to get ahead of this ... [employers] are going to be very successful," Demers said.

"We don't want to take away anybody's job."