VANCOUVER -- People who have never smoked marijuana could be most at risk of overdosing on cannabis-infused edibles that will soon be on store shelves across the country, warns a public health physician who says first-time users may keep noshing away while expecting a high, only to experience a racing heart, anxiety and panic attacks.

Dr. Lawrence Loh, adjunct professor at the Dalla Lana School of Public Health at the University of Toronto, said overdose from overconsumption often means a trip to the emergency room for those who are unaware that feeling the mellow effects of pot from edibles can take several hours because of the time needed to digest and absorb food into the small intestine versus quickly inhaling the drug through the lungs.

Seniors are especially at risk because of a slower metabolism, Loh said of non-lethal overdose from edibles, which federal regulations limit to an individual serving size of a 10-milligram dose of THC, the psychoactive ingredient in marijuana.

However, someone who eats an entire package of cannabis-infused product could be taking in a whopping 100 milligrams of THC and putting themselves at risk, even though regulations require products to be individually wrapped in 10-milligram serving sizes.

“I think the big thing for anyone in the public, especially cannabis-naive individuals or people who have edibles around with children at home, is to first and foremost avoid overdosing,” Loh said.

“There's psychotic reactions so people may lose touch with reality, sometimes in the form of hallucinations or delusions and also anxiety or panic attacks along with decreased judgment.”

Loh is co-author of a commentary published Monday in the Canadian Medical Association Journal on the health risks of cannabis edibles.

Short-term effects of edibles are not the only issue of concern, he said.

“There are still those longer term, chronic risks around edibles, particularly around addiction and also the risk of exacerbation of existing mental-health issues that we might be worried about in the longer run with cannabis edibles as well as any form of cannabis,” he said.

Regulations governing edibles, beverages, vapes and topical forms of cannabis came into effect last October, a year after Canada legalized fresh or dried bud, oil, plants and seeds.

Cannabis edibles such as cookies, chocolate and gummies were available for sale starting in December in all provinces except Ontario, Quebec and Alberta, where consumers can access them in mid-January.

In Ontario, for example, edibles will be available as of this week in stores, and then online in mid-January through the provincial distributor as a part of a slow rollout over the next few months.

A University of Colorado School of Medicine study published last March in the Annals of Internal Medicine says an increase in emergency-room visits related to edibles prompted health experts to issue warnings about cardiac and psychiatric issues in the state that began selling recreational marijuana in 2014. Packaging, potency and labelling restrictions on edibles did not come into effect until a year later before being tightened to require labels to prominently display the potency of psychoactive ingredients.

Loh said there's a lack of data on edibles in general but consumers should also beware that illicit, unregulated products still exist and could be problematic because of issues such as mould.

The Canadian Centre on Substance Use and Addiction recommended last July that anyone who has never smoked or vaped cannabis should not consume more than 2.5 milligrams of THC in a product and wait to feel the effects before taking more.

Dr. Jeff Finkler, an emergency-room physician at St. Paul's Hospital in Vancouver, said he sees plenty of patients, mostly females in their late teens and early 20s, who come in having panic attacks or anxiety from eating too much of a cannabis-infused food and sometimes mixing it with alcohol or other substances.

“The thing that people forget is that there's a delayed response,” he said, adding users often think the recommended dosage couldn't possibly pack a buzz. They are sometimes given a benzodiazepine to counteract the effects of an overdose before being sent home.

“Don't cut off more than the actual dose just because it looks so small. You don't want to eat the whole thing. That little thing's got eight doses or 10 doses,” he said of a package.

“It's not like smoking. When you start to feel weird you can stop inhaling. But when you ingest it, man, it's on board.”

While 10 milligrams of THC is the recommended dosage, the psychoactive ingredient of marijuana in a food is hard to measure, he said.

“It requires very sophisticated analytical equipment and it's even more complicated when they use chocolate because people think it enhances the viability of the THC but chocolate interferes with the measurement of the actual amount.”

“Start low, go slow, and wait. Be patient if you're going to take the edibles.”