Smoking marijuana could possibly double a young person's risk of suffering a stroke, according to new research.
"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 the senior researcher, Dr. Alan Barber, a professor of clinical neurology at the University of Auckland in New Zealand.
Barber, who is also a stroke specialist at the Auckland City Hospital, decided to embark on the study after noticing an unusual number of strokes among young patients who had apparently smoked dope.
So Barber and his research colleagues, with the approval of the hospital's ethics committee, began testing urine samples from patients, aged 18 to 55, who were admitted to the hospital for either a stroke or a transient ischemic attack, commonly known as a TIA or mini-stroke.
They ran tests on 160 patients and about 16 per cent of them tested positive for recent cannabis exposure.
The researchers also conducted drug tests on a random sample of 160 non-stroke patients of similar age and background. Among these patients, who served as a control group, only 8 per cent showed evidence of dope consumption.
"When you control for age, sex and ethnicity, the stroke patients who had used marijuana were twice as likely to have had a stroke than the control participants," Barber said.
The case-controlled study, which was presented in Hawaii at a scientific conference of the American Stroke Association, provides the strongest evidence to date of an association between cannabis and stroke, he said.
The research, however, has limitations. It is based on a relatively small sample and the findings need to be replicated in a larger group.
Furthermore, most of the stroke patients who showed evidence of cannabis exposure also smoked tobacco – which is another risk factor for stroke.
But Barber believes that it is the marijuana, and not the tobacco, that's boosting the stroke risk. He noted that previous studies have demonstrated that cannabis can increase heart rate, lead to an irregular heartbeat and constrict blood vessels – all of which can increase the chances of having a stroke or TIA.
Even so, it must also be kept in mind that the overall risk of having a stroke is comparatively low for a young person.
"Doubling of a low risk is still a relatively low risk," Barber acknowledges.
In his study, the mean age of those tested for cannabis was 44. For that age group, you'd expect an incidence rate of 35 to 55 strokes a year for every 100,000 men in the general population and between 21 to 24 strokes a year for every 100,000 women.
"Our study suggests cannabis may double these numbers," Barber said.
Although the absolute number of strokes may be small among young marijuana smokers, Barber thinks the public should be made aware of the risk. Another recent study, also conducted in New Zealand, suggested that using marijuana at a young age can hamper proper brain development. And other research suggests that inhaling the hot smoke can damage the lungs and possibly contribute to the development of emphysema, he noted.
"While there is a perception that cannabis is a relatively harmless substance, it is not actual that harmless."