The study showed that ischemic stroke and transient ischemic attack (TIA) patients 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 Professor Alan Barber, lead investigator for the study and Neurological Foundation professor of clinical neurology at the University. “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.”
Professor Barber this week presented the study findings to the American Stroke Association’s International Stroke Conference 2013 in Honolulu. The study included 160 ischemic stroke/TIA patients aged 18-55 years who had urine screens upon admission to the hospital.
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, says Professor Barber. “These patients usually had no other vascular risk factors apart from tobacco, alcohol and other drug usage. It’s challenging to perform prospective studies involving illegal substances such as cannabis because “questioning stroke and control patients about cannabis use is likely to obtain unreliable responses,” he says.
The study provides the strongest evidence to date of an association between cannabis and stroke, says Professor Barber. 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 use and not tobacco,” says Professor Barber, who hopes to conduct another study to determine whether there’s an association 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,” he says. “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, says Professor Barber. “People need to think twice about using cannabis, because it can affect brain development and result in emphysema, heart attack and now stroke.”
The study was funded by the Auckland District Health Board’s A+ Trust. Co-authors were: Dr Neil E. Anderson (ADHB), Dr Heidi Pridmore, Dr Venkatesh Krishnamurthy, Dr Sally Roberts, Dr David A. Spriggs, and Dr Kristie Carter.
The University of Auckland