Marijuana Users’ Risk of Deadly Complication Doubles After Rare Type of Bleeding Stroke


The study is the largest to examine the impact of THC on individuals with aneurysmal subarachnoid hemorrhage.

Among individuals with aneurysmal subarachnoid hemorrhage (aSAH), a type of bleeding stroke, recent cannabis users were more than twice as likely to develop dangerous complications that could result in death or greater disability, according to research results published in Stroke, a journal of the American Stroke Association of the American Heart Association.

The study is the largest to examine the impact of tetrahydrocannabinol, or THC, of cannabis on complications after an aSAH, a rare but severe form of stroke.

"We're all vulnerable to a bleeding stroke or a ruptured aneurysm. However, if you're a routine marijuana user, you may be predisposed to a worse outcome from a stroke after the rupture of that aneurysm," Michael Lawton, MD, president and CEO of Barrow Neurological Institute in Phoenix, Arizona, said in a statement.

This type of stroke can result in neurological disabilities in about 66% of individuals and death during the follow up period in approximately 40% of individuals, according to the statement.

The immediate treatment of aSAH can prevent and stop further bleeding. However, in the 14 days following aSAH, individuals can experience worsening symptoms that could result in more brain damage. This complication is called delayed cerebral ischemia and is the leading cause of death and disability after an aSAH stroke.

Investigators of the study analyzed data on more than 1000 individuals who had been treated for aSAH at Barrow Neurological Institute between January 1, 2007 and July 31, 2019. All individuals were treated to stop the bleeding either noninvasively by treading a slim tube through the blood vessel to the base of the aneurysm and releasing coils that fold to fill in the pace and provide a barrier to further bleeding or through open surgery to clip off the base of the aneurysm .

Urine toxicology screening was done on each of the individuals admitted with ruptured aneurysms. Investigators compared the occurrence of delayed cerebral ischemia in 46 individuals, averaging aged 47 years and 41% female, who tested positive for THC, and 968 individuals, averaging aged 56 years and 71% female, who tested negative for THC.

A positive urine screen for THC reflects cannabis exposure within 3 days for a single use to within approximately 30 days for frequent heavy use.

The individuals who recently used cannabis did not have significantly larger aneurysms or worse stroke symptoms when admitted to the hospital and they were not more likely to have high blood pressure or other cardiovascular risk factors than individuals who tested negative for THC.

Recent cannabis users were also significantly more likely to have tested positive for other substances, including cocaine, methamphetamines, and tobacco, compared with those who tested negative for THC.

Of all individuals, approximately 36% developed delayed cerebra ischemia, approximately 13.5% died, and approximately 50% were left with moderate to severe disability, and .

After adjusting for several other characteristics as well as recent exposure to other illicit substances, individuals who tested positive for THC were 2.7 times more likely to develop delayed cerebral ischemia, 2.2 times more likely to die, and 2.8 times more likely to have long-term moderate to severe physical disability.

The study does not specifically address how cannabis raises the risk of delayed cerebral ischemia and vasospasm.

The study’s limitations include being conducted at a single institution and not being able a head-to-head analysis of those who used cannabis and those who did not.


Marijuana users’ risk of deadly complication doubles after rare type of bleeding stroke. Science Daily. News release. January 6, 2022. Accessed January 11, 2022.

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