There's only one way to completely avoid harm when using pot, according to Dr. Benedikt Fischer: Don't use it at all.

But with the federal government aiming to legalize marijuana by July 2018, clearly not everyone in Canada is expected to choose abstinence.

In fact, statistics suggest upwards of three million Canadians are already using the drug. So Fischer and several colleagues have reviewed the scientific evidence and put together a new set of guidelines aimed at minimizing the risks of pot use.

The guidelines, being published in the June 2017 issue of the American Journal of Public Health, were formally announced at a news conference in Ottawa today.

'Always will come with some risks'

"Let me be very clear: these are not guidelines for risk-free cannabis use. That doesn't exist. It always will come with some risks," said Fischer, a senior scientist with Toronto's Centre for Addiction and Mental Health and a psychiatry professor at the University of Toronto.

But those risks can be minimized, just like with drinking or sexual activity, Fischer said.

Dr. Benedikt Fischer of the Centre for Addiction and Mental Health speaks to reporters after appearing before a Liberal Senate caucus meeting and panel discussion on marijuana on Parliament Hill last year. Fischer and his colleagues have released harm-reduction guidelines for people who decide to use pot. (Sean Kilpatrick/Canadian Press)

"There's a lot of room for modification on the part of the users — how they use, when they use, what they use— that will influence their risk for acute and chronic health outcomes."

The guidelines have been endorsed by several major medical groups, including the Canadian Medical Association (CMA) and the Council of Chief Medical Officers of Health.

It's best to wait

If you're not going to avoid pot altogether, Fischer said, a few of his 10 tips still stand out as being especially significant.

One is to wait until you're older to start using marijuana, particularly if you're under 16. (The federal legislation proposes a minimum legal age of 18.)

Young people are more vulnerable to physiological, psychological and behavioural problems because of pot use, he said.

"We know young people are the most vulnerable but that's also where most of the cannabis use is happening at the moment and will likely continue to happen."

Dr. Benedikt Fischer, a senior scientist with Toronto's Centre for Addiction and Mental Health and a psychiatry professor at the U of T, says marijuana use poses risks for young people. 1:01

He cites research showing those who started using by age 14 were four times more likely to develop cannabis dependance and three times more likely to get into a car crash than those who started after 21. Research also shows associations between early use and mental-health problems such as depressive and psychotic symptoms.

Reduce your use

"Watch and reduce your patterns of frequency of use," said Fischer. "It makes an enormous difference in acute and chronic health outcomes whether someone uses cannabis once or twice a week or daily."

That tip is backed up by scientific research showing frequency/intensity of use is associated with mental-health problems, cardiovascular problems, motor vehicle accidents and suicide.

Don't get behind the wheel

While marijuana use will be legalized, driving high won't be. Fischer said many cannabis users underestimate the risk of an accident.

"Absolutely do not use cannabis and get into a car, and drive within less than at least six hours of consumption."

The studies used to back up the guidelines show the risk of a crash increases anywhere from 1.3 to four times after cannabis use. They also suggest the risk is much higher when pot is combined with alcohol.

Dr. Benedikt Fischer, a senior scientist with Toronto's Centre for Addiction and Mental Health and a psychiatry professor at U of T, talks about avoiding marijuana impairment while driving. 1:02

Don't smoke it

The statistics show that when most people use marijuana, they smoke it, but there are safer options, according to Fischer's research.

Smoking can harm your lungs and respiratory system.

"There are alternatives that are safer in certain ways but they come with other potential risks we have to be aware of. "

Edible marijuana products don't represent the same threat to your lungs but can lead to more severe impairment, said Fischer. In Colorado, where marijuana is legal, there have been serious concerns raised about adults and especially children winding up in the hospital after consuming edible marijuana products.

Canada's proposed pot legislation doesn't tackle the question of edibles. The government has said they'll be made available at a later date, once regulations to deal with them have been developed.

Ian Culbert, executive director of the Canadian Public Health Association, said there must be strict regulation and a limited range of products available initially. Edibles must have clear identification of dosage and servings, and come with education about how it takes longer to take effect than smoking.

"You eat a brownie, you don't feel anything. Well you have some more, you don't feel anything, and you have some more," he said during the news conference. "Then suddenly you're in the ER because you've overdosed on cannabis."

Medical marijuana is already a booming business across Canada. Federal legislation has been introduced to regulate the sale of legal cannabis as early as July 1, 2018. (Matthew Staver/Bloomberg)

Using vaporizers, or "vaping," has been shown to reduce toxic intake and the risk to lungs, but Fischer's work points out that there have been no rigorous studies on the long-term effects.

Other recommendations

Identify and choose lower-risk cannabis products, notably those with lower THC levels.

Don't use synthetic cannabis products such as "Spice" and "K2", which can even lead to death.

If you smoke cannabis, avoid practices like "deep inhalation" and "breath holding".

Avoid pot altogether if you are at risk of mental-health problems or are pregnant.

Avoid combining risks, such as starting young and smoking high-potency products

'Important, evidence-based information'

Federal Health Minister Jane Philpott said in a statement Health Canada would "explore further dissemination" of the guidelines when the legislation to legalize cannabis comes into effect.

She said the guidelines are "important, evidence-based information to help cannabis users reduce the health and safety risks associated with cannabis use.

"I commend the authors of the guidelines, particularly Dr. Benedikt Fischer of the Centre for Addiction and Mental Health, for their dedication to producing this valuable resource."

In an interview, the government's point man on pot, former Toronto police chief Bill Blair, went even further in his praise for the guidelines.

"I think they're excellent.

Bill Blair, parliamentary secretary to the minister of justice, has been the government's point man on cannabis legalization and welcomes the CAMH guidelines. (Sean Kilpatrick/Canadian Press)

"I would never presume to speak on behalf of the government or the minister, but I know the people who have done this work. I've had the benefit of a number of different conversations with the people who have done this work. I've spoken to the CMA as well and I think these frankly ... are long overdue."

The decisions taken by governments could go a long way towards affecting the risks associated with cannabis use, according to Fischer. For example, making sure edible marijuana products are sold in limited quantity to avoid over-consumption can make a big difference, he says, as can including warning labels.