A study out of New Zealand appears to show a link between marijuana use and strokes in young adults.

Researchers tested the urine of 150 patients who'd had ischemic strokes (a cutting off of blood supply) and 10 who'd had transient ischemic attack ("mini-strokes"), all aged between 18 and 55. They found that 16 per cent of these patients tested positive for marijuana use, compared to 8.1 per cent of patients in a control group who'd been hospitalized with other ailments.

Estimates vary as to how long marijuana is detectable in urine. For a one-time high, it could be about a week. For heavy users, it could be a month or more.

"This is the first case-controlled study to show a possible link to the increased risk of stroke from cannabis,” said Alan Barber, the study's lead investigator and professor of clinical neurology at the University of Auckland. “Cannabis has been thought by the public to be a relatively safe, although illegal substance. This study shows this might not be the case; it may lead to stroke.”

The soundbite-friendly summation is that stroke patients were 2.3 times more likely to be pot smokers, but that's hardly the full story.

"It's a small study, it does suggest that the use of marijuana was greater in the strokes, particularly the younger strokes," said American Stroke Association spokesperson Ralph Sacco. "There are problems however in that there are certain variables that they could not control for in this study."

In particular, the big, smokey elephant in the room is tobacco. All but one of the stroke patients who tested positive for cannabis use were smokers. It's well known that smoking cigarettes doubles stroke risk.

"They were not able to control for tobacco use," said Sacco. He added that other factors such as diet, alcohol use and head injuries were also not accounted for.

"I think we still don't know what the actual relationship is being driven by," he said.

Despite these questions, Barber is convinced that marijuana is to blame.

"We believe it is the cannabis and not tobacco,” said Barber. He plans to conduct another study to pinpoint marijuana's potential stroke risks independent of tobacco use, although he adds that, “this may prove difficult given the risks of bias and ethical strictures of studying the use of an illegal substance."

Barber said there have been previous case reports of stroke occurring shortly after marijuana use.

"We know cannabis can cause changes in blood pressure and heart rate that are associated with increased stroke risk. Importantly, it can also cause heart palpitations," Barber told EverydayHeath. He added that heart palpitations can be an indicator of atrial fibrillation (a type of irregular heartbeat) that has a strong association with stroke.

“People need to think twice about using cannabis,” because it can affect brain development and result in emphysema, heart attack and now stroke, Barber said.

Marijuana is the most widely-used illicit drug and is used by 9.1 per cent of Canadians over the age of 15, according to 2011 statistics.

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