As medical and recreational marijuana becomes legal in more and more places, experts worry that there isn't enough science on the risks of the drug, especially for patients with heart disease.

In a new case report, doctors describe the heart attack of a man who ate a lollipop laced with high levels of THC, marijuana's psychoactive ingredient. This patient's story may serve as a warning that cannabis isn't as benign as some would like to think, doctors wrote this week in the Canadian Journal of Cardiology.

The 70-year-old Canadian man, who had pre-existing heart disease, suffered a heart attack half an hour after consuming most of a lollipop that contained 90 milligrams of THC. The man had hoped that it would help with arthritis pain and allow him to sleep. The dose in the lollipop was far greater than what people typically inhale with a single marijuana joint, 7 milligrams, the researchers note.

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"With access to marijuana legal now in Canada, it's going to be accessible to a larger proportion of the population and it's more likely that some of them will have heart disease," said study co-author Dr. Rob Stevenson, a cardiologist at the New Brunswick Heart Center in St. John, New Brunswick. "This could be the canary in the coal mine."

The man had already been diagnosed with atherosclerosis and had bypass surgery, but he was taking medications to treat the condition, and his disease was "stable" at the time he consumed the edible cannabis, said lead study author Dr. Alex Saunders, chief resident of the internal medicine program at the St. John's site for Dalhousie University. "After his bypass surgery he had no repeats of chest pain other than this one," Saunders said.

The man had smoked marijuana in his youth and had fond memories of it, Saunders said. But once the effects of the high-dose THC in the lollipop started to hit, the man's blood pressure and heart rate quickly shot up. "He described fearful hallucinations," Saunders said. "He was very afraid he was going to die."

By the time family members got to him, "he was not only having hallucinations, but also intense chest pain," Saunders said, adding that the terror the man experienced may have been too much for his heart.

Once at the hospital, doctors confirmed that he'd had a heart attack. The man survived his heart attack, but tires more quickly than before with exercise.

Saunders worries that with marijuana now legal in Canada, increasing numbers of people with heart disease will be using it and some of them will be at risk for heart attacks. "When I was in my rheumatology rotation, over half of my patients were asking if marijuana would help with the aches and pains that don't get better with traditional medicine," she said.

And while many would have avoided cannabis before, "now that it's legal they don't feel as bad," Saunders said.

"One of the most reliable acute effects of the THC in cannabis is that it increases heart rate," said Ryan Vandrey, a researcher who wasn't involved in the case report. "And it's dose dependent. Even at modest doses you can get increases in heart rate of 20 to 30 beats per minutes. And it can go higher. If someone with cardiovascular risk factors experiences a short-term bump in heart rate, that would be a concern."

Vandrey, a psychiatry researcher at Johns Hopkins Medicine in Baltimore, was especially disturbed by the high dose of THC in the lollipop. "Part of my frustration with products like this is that nobody is going to take just a couple of licks and then put it away," he said. "There should be no circumstance where you get a product and you're not supposed to consume the whole thing and it's not clear when you're supposed to stop."

In an editorial accompanying the case report, Dr. Neal Benowitz of the University of California, San Francisco, outlines the different mechanisms by which THC can affect the heart and cautions doctors to keep these in mind when deciding whether and how to use cannabis to treat patients with heart disease.