Experts warn there could be unexpected health risks from eating foods containing the drug cannabis. Those risks include accidental overdose, children eating them accidentally and unexpected effects in older adults.

The commentary by doctors Lawrence Loh and Jasleen K. Grewaland appeared in the Canadian Medical Association Journal.

Loh is with the Dalla Lana School of Public Health at the University of Toronto. He said, "What we really want the public to know is that legal doesn't mean safe. People need to know that how they react will depend on the manner cannabis is consumed, the amount that is consumed and the person's own metabolism..."

Loh said it can take hours for the cannabis high to take effect if the drug is eaten instead of smoked. So, he said, people might eat more of the cannabis as they wait for the high to happen.

While a cannabis overdose will not kill you, it can be unpleasant, Loh said. He added, "We suggest people start with a low dose and go slow."

Loh and Grewaland also advise older adults be extra careful with edible cannabis. They could be at greater risk for falls and injury, especially those who are not used to the drug's effects.

Loh also warns that adults should be mindful that edible cannabis products might interest children. Loh said the drugs should be stored carefully "to make sure kids can't get into it."

Loh and Grewaland also suggest that doctors add questions about cannabis to those they usually ask a patient, so they can offer education and advice.

A warning such as this one "is really important," said Dr. Michael Lynch. He is medical director of the Pittsburgh Poison Center and with the University of Pittsburgh School of Medicine in Pennsylvania.

Lynch said the risk of dying from an overdose is low. But he added that the risks of medical problems or injury is very real. "The greatest risk is to the young and the old," he said.

Lynch said those who overdose would be at risk for falls, vomiting and weakness.

An increase in heart rate and blood pressure could also be more of a problem for older people, Lynch said.

He added, "People need to be educated about the risk so these outcomes can be avoided."

I'm Caty Weaver.

Linda Carroll reported this story for the Reuters news agency. Jonathan Evans adapted it for Learning English. Caty Weaver was the editor.

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consume -v. to eat or drink (something)

metabolism -n. the chemical processes by which a plant or an animal uses food, water, etc., to grow and heal and to make energy

dose -n. the amount of a medicine, drug, or vitamin that is taken at one time

vomit -v. to have the food, liquid, etc., that is in your stomach come out through your mouth because you are sick

outcome -n. something that happens as a result of an activity or process