Smoking cannabis increases the risk of stroke as it narrows arteries in your head, a study warned.
Out of a study of stroke victims – 45 per cent – of cannabis users had blood vessels constricted by plaque in their skulls, compared to just 14 per cent of non-users.
The study also found marijuana users suffered strokes at a younger age than those who did not smoke the drug.
The approach could help researchers begin to identify possible mechanisms for stroke and help stop it.
The study by The University Hospital of Strasbourg looked at all patients under age 45 admitted with ischemic stroke from 2005 to 2014.
Of the 334 patients who suffered stroke, 58 were marijuana users.
Ischemic stroke is caused by a blockage that interrupts or reduces blood flow to the brain as opposed to haemorrhagic stroke, which occurs when a blood vessel in the brain leaks or ruptures.
In the cannabis smokers, the ischemic stroke was more likely to be caused by intracranial arterial stenosis, a condition where there is narrowing the arteries inside the skull caused by a build-up of plaque.
Intracranial arterial stenosis was found in 45 per cent of the marijuana users in the study compared to 14 per cent of the non-users.
The drug smokers were younger, more likely to be male, more likely to smoke tobacco, and more likely to have other lifestyle risk factors than non-users in the study.
Cardio embolism, a blood clot formed elsewhere in the body that moves to the brain, was the most common cause of ischemic stroke in non-marijuana users in the study.
Strokes in the young are of particular concern, the authors say ‘because of the longer expected survival relative to older patients’ – although younger patients also had better chances of recovery.
Investigators found 29 per cent of strokes in non-users were caused by cardio embolism compared to only 14 per cent in the marijuana users.
Out of both groups, five died suffering a stroke, and 18 per cent suffered a long term disability.
Neurologist Dr Valerie Wolff said: ‘Fighting stroke must remain a priority, including in young adults.
‘The first step may be to inform the public regarding the potential occurrence of stroke associated with cannabis and other lifestyle risk factors.’
The study was published in the Journal of the American College of Cardiology.
The journal's editor in chief Dr Valentin Fuster added: ‘The effects of cannabis have been considered benign for a long time; however, evidence continues to build about the relationship of its use with stroke.’