(CBS News) -- Marijuana may trigger strokes in young adults, according to preliminary research presented today at an international medical conference.
New Zealand researchers reviewed urine samples taken from 160 stroke sufferers between the ages of 18 and 55, and discovered the patients were more than twice as likely to have pot, or cannabis, in their system.
"Cannabis has been thought by the public to be a relatively safe, although illegal substance," study author Dr. P. Alan Barber, professor of clinical neurology at the University of Auckland in New Zealand, said in a statement to the American Heart Association. "This study shows this might not be the case; it may lead to stroke."
Marijuana is the most commonly used illicit drug in the United States, taken by 7 percent of Americans according to a 2012 government survey.
The drug is illegal in the United States on a federal level, however, Washington and Colorado became the first states to pass laws legalizing recreational pot use last November. Eighteen states plus the District of Columbia also have laws permitting the use of medical marijuana.
In what they call the first case-controlled study to find a link between marijuana use and strokes, researchers enlisted 150 patients who had an ischemic stroke and 10 who had a transient ischemic attack (TIA).
Strokes, or brain attacks, are caused by disruptions of blood flow to the brain. About 85 percent of strokes are ischemic, meaning they are caused by blood clots or plaque deposits in linings of blood vessels that stop blood flow to the brain. That's different from a less-common hemorrhagic stroke that occurs when a blood vessel in the brain bursts. Symptoms of strokes include severe headache, sudden numbness or weakness of the face or limbs, sudden confusion or trouble speaking, vision problems, dizziness and loss of coordination.
People may also experience a TIA, also called a "mini" or "warning" stroke, a temporary blockage that causes stroke symptoms that go away after a few minutes without causing lasting damage. About one-third of people who have a TIA go on to have a stroke within a year, according to the American Heart Association.
The researchers found 16 percent of the subjects who went to the hospital following a stroke episode had marijuana in their system, compared to 8.1 percent of control subjects who came to the hospital. Barber adds there have been case reports of people with no other vascular risk factors having a stroke or TIA hours after using marijuana.
However, all but one of the stroke patients who had marijuana in their urine also used tobacco. Barber still believes the marijuana was the culprit.
"For starters, this is a young age group to be having strokes, and many didn't have any of the traditional risk factors. And some patients had a stroke while actually smoking cannabis," he told EverydayHealth. "We know cannabis can cause changes in blood pressure and heart rate that are associated with increased stroke risk. Importantly, it can also cause heart palpitations, [a sign of atrial fibrillation]. And atrial fibrillation is very strongly associated with stroke," he added.
Every year more than 795,000 Americans have a stroke, 610,000 who have one for the first time. About 130,000 Americans die from a stroke each year, about one death every four minutes.
The study was presented Feb. 6 at the American Stroke Association's International Stroke Conference in Honolulu.