Smoking marijuana may increase the risk of stroke in people under age 55, a new study from Australia suggests.
In the study, young stroke patients were about two times more likely to have cannabis detected in their urine compared to patients who were of a similar age, but hadn't had a stroke.
Although it's an illegal drug, "cannabis is generally perceived as having few serious adverse effects," said study researcher Dr. P. Alan Barber, a professor of clinical neurology at the University of Auckland in New Zealand. The findings suggest this may not be the case, Barber said.
However, the study only found an association, and not a cause-effect link. Although the researchers took into account each patient's age, gender and race, it's possible other factors might have been responsible for the link. For instance, many of the cannabis users also smoked tobacco, so it was impossible for the researchers to disentangle the effects of tobacco from those of marijuana. Further studies should be conducted to determine if marijuana smoking really can cause stroke, the researchers said.
Some physicians have reported cases of young patients with no risk factors for stroke experiencing one after heavy marijuana smoking, but few rigorous studies have investigated the link.
In the new study, Barber and his colleagues analyzed information from 160 patients between ages 18 to 55 who had suffered either an ischemic stroke, which occurs when a blood vessel to the brain is blocked, or a transient ischemic attack, also called a mini-stroke, which is caused by a temporary blockage of a blood vessel. For comparison, the study also included 160 people who visited the hospital for other reasons besides stroke.
Screening tests of patients' urine showed that 15.6 percent of stroke patients tested positive for marijuana use, compared to 8.1 percent of the other hospital patients. Cannabis users tended to be similar to nonusers in age, cause of stroke and risk factors for stroke and heart disease, such as high blood pressure and high cholesterol.
Cannabis use has effects on the heart and blood vessels that make a link with stroke possible, Barber said. For instance, cannabis use increases the risk of atherosclerosis, or the buildup of plaque in the arteries, which reduces blood flow and increases the risk of stroke, Barber said.
The study will be presented this week at the American Stroke Association's International Stroke Conference in Honolulu.
Pass it on: Smoking marijuana may be a risk factor for stroke.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.