麻豆传媒

HONOLULU -- Middle age stroke patients were 2.3 times more likely to be pot smokers than healthy middle age controls, according to a study slated for presentation here at the International Stroke Conference (ISC).

"This is the largest case-controlled study ever done to show a possible link to the increased risk of stroke from cannabis," P. Alan Barber, MD, PhD, a professor of clinical neurology at the University of Auckland in New Zealand, told 麻豆传媒 in an interview.

The study will be formally presented at the conference on Wednesday. The ISC released the information after an Australian publication reported the finding based on an embargoed press release.

Barber's interest in the topic arose when he encountered a 30-something stroke patient who had none of the typical risk factors associated with stroke such as hypertension or diabetes -- but the patient smoked pot.

He and his colleagues then searched the literature and found similar case reports associating marijuana smoking with stroke in younger adults who did not have typical risk factors.

"At that point, we decided to test all young stroke patients for the presence of cannabis in their urine," Barber said. "We found a high proportion of positive tests in the first 40 patients, so we expanded the study."

The current study comprises a cohort of 160 patients (100 of them men) with an average age of 45 (range 18 to 55) who had a stroke or TIA. Most patients (94%) had an ischemic stroke; only 6% had a TIA.

For a control group, the ethics committee allowed the researchers to use a matched cohort of 160 patients who had not had a stroke and who had had urine tests for various reasons.

The problem with the controls, Barber said, was that researchers knew only their age, sex, and ethnicity. The fact that they weren't able to adjust for tobacco use was a big limitation of the study, he said.

Nevertheless, Barber and colleagues found that 16% of stroke patients were positive for cannabis compared with 8% of controls.

"That was surprising to us, that one in six stroke patients also had cannabis in their system," he told 麻豆传媒.

When researchers performed a logistic regression analysis adjusted for age, sex, and ethnicity, the only factor associated with increased risk of ischemic stroke or TIA was the use of marijuana (OR 2.30, 95% CI 1.07 to 4.95).

"The study provides the strongest evidence to date of an association between cannabis and stroke," Barber said, "but the association is confounded because all but one of the stroke patients who were cannabis users also used tobacco regularly. We could not find out to what extent -- if at all -- controls used tobacco."

However, Barber said he believes the stroke risk is from marijuana use and not tobacco.

"We think causality is plausible, because some of the patients had a stroke within days of using the cannabis. We know cannabis causes palpitations such as atrial fibrillation, and atrial fibrillation is strongly associated with stroke. We also know that cannabis causes constriction of brain vessels," Barber said.

He said his next step is to conduct a similar study where he is able to adjust for tobacco use.

The results of the study are particularly important, he said, because pot smoking is generally considered benign, and several states in the U.S. have legalized it in one form or another.

"Whether marijuana is legal or not is up to regulatory authorities, but it's important to pause and think that there may be risks associated with smoking marijuana," he concluded, adding that further research is needed to explore these risks in more detail.

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