The case of a young man who suffered a stroke more than once after smoking marijuana adds to evidence that the drug can, in rare cases, have such serious consequences, according to researchers.

On three separate occasions, the 36-year-old man suffered a stroke shortly after smoking a large amount of marijuana. He had no known risk factors for stroke and no signs of atherosclerosis, a narrowing and hardening of the arteries over time that can lead to a heart attack or stroke.

Instead, the timing of the strokes points to the patient’s marijuana use - and possibly his habit of combining it with alcohol - as the culprit, according to his doctors.

“Marijuana seems to be a risk factor for stroke,” said Dr. Juan Carlos Garcia-Monco of the Hospital de Galdacano in Vizcaya, Spain. The risk, albeit low, may be higher when marijuana is used along with alcohol or other drugs, he told Reuters Health.

Garcia-Monco and his colleagues report on the case in the March issue of the Journal of Neurology, Neurosurgery and Psychiatry.

Marijuana is known to have a number of short-term effects on the cardiovascular system, including speeding the heart rate, raising or lowering blood pressure, and even elevating the risk of heart attack in the hour after use. But only rarely has the drug been linked to stroke; one recent report described the cases of three teenage boys who suffered strokes after smoking marijuana, two of whom died.

This latest case, Garcia-Monco said, is different in that the patient had a stroke on three separate occasions, with each following a bout of heavy marijuana use.

In the first instance, the man lost his ability to speak and suffered a seizure after smoking marijuana and having a few drinks at a party. One year later, he again became unable to speak and suffered weakness on one side of his body after smoking pot at another party.

The third incident came roughly a year later, when the man had some hearing loss after an episode of heavy marijuana use and drinking. Each time, doctors found tissue damage in the brain.

It’s not entirely clear how marijuana may cause a stroke, which occurs when blood flow to the brain is cut off and brain tissue begins to die. A sudden constriction of the arteries after smoking the drug may be to blame, according to Garcia-Monco, but that’s not yet certain.

Some past research has found that marijuana users may develop changes in blood flow to the brain that makes it harder for blood to diffuse through the small vessels in the brain.

“We believe that marijuana-related stroke must be infrequent, since marijuana use is so frequent and this association is only rarely reported,” Garcia-Monco said. However, he added, even if the side effect is rare, it is a serious one.

This case and others show that marijuana is not as innocuous as many think, according to an editorial published with the report.

“In that recreational cannabis use appears not to be as harmless as was thought,” writes Dr. Dominique Deplanque of the University of Lille in France, “there is a need to improve public information.”

Better recognition of marijuana-related stroke, he notes, could allow for larger studies to see whether some people may have an inherited predisposition to the complication.

Garcia-Monco suggested that doctors screen for the presence of marijuana and other drugs whenever a young person inexplicably suffers a stroke.

SOURCE: Journal of Neurology, Neurosurgery and Psychiatry, March 2005.