Brain research scientists from the University of Auckland showed that those who suffered ischemic stroke (loss of blood supply to the brain) or transient ischemic attack (TIA) when blood flow to the brain stops momentarily) were 2.3 times more likely to have cannabis detected in urine tests as other age and sex matched patients.
"This is the first case-controlled study to show a possible link to the increased risk of stroke from cannabis," said Alan Barber, lead study investigator and professor of clinical neurology at Auckland, according to an Auckland statement.
"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," said Barber.
His study included 160 ischemic stroke/TIA patients aged 18-55 years who had urine screens upon hospitalisation.
Among the patients, 150 had ischemic stroke and 10 had TIAs.
Sixteen percent of patients tested positive for cannabis, and were mostly male who also smoked tobacco, while only 8.1 percent of controls tested positive for cannabis in urine samples.
Researchers found no differences in age, stroke mechanism or most vascular risk factors between cannabis users and non-users.
In previous case reports, ischemic stroke and TIAs developed hours after cannabis use, said Barber.
"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, he said.
Barber presented these findings at the American Stroke Association's International Stroke Conference 2013 in Honolulu.