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Study finds link between marijuana use, stroke


Marijuana, the most widely used illicit drug, may double stroke risk in young adults, according to a New Zealand study.

In the study, ischemic stroke and transient ischemic attack patients were 2.3 times more likely to have cannabis detected in urine tests compared with other age- and sex-matched patients, researchers said.

“This is the first case-controlled study to show a possible link to the increased risk of stroke from cannabis,” P. Alan Barber, MD, PhD, the study’s lead investigator and a professor of clinical neurology at the University of Auckland, said in a news release. “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 study included 160 ischemic stroke or TIA patients, ages 18 to 55, who had urine screens upon admission to the hospital. Among those patients, 150 had ischemic stroke and 10 had TIAs, while 16% had positive drug screens, mostly males who also smoked tobacco, That rate compared with 8.1% of controls who tested positive for cannabis in urine samples. The researchers found no differences in age, stroke mechanism or most vascular risk factors between marijuana users and nonusers.

In previous case reports, ischemic stroke and TIAs developed hours after cannabis use, Barber said. “These patients usually had no other vascular risk factors apart from tobacco, alcohol and other drug usage.”

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 believe it is the cannabis and not tobacco,” said Barber, who hopes to conduct another study to determine whether any association exists between cannabis and stroke independent of tobacco use. “This may prove difficult given the risks of bias and ethical strictures of studying the use of an illegal substance. However, the high prevalence of cannabis use in this cohort of younger stroke patients makes this research imperative.”

Physicians should test young people who come in with stroke for cannabis use, Barber said.

The study is scheduled for presentation in Honolulu at the American Stroke Association’s International Stroke Conference 2013.


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