Smoking Cannabis Increases Stroke Complication Risk
Patients who had tested positive for THC were 2.8 times more likely to have a physical disability following a stroke.
Stroke is a leading cause of long-term disability and mortality worldwide. Understanding risk factors and outcome modifiers is essential for guiding both patient management and public health recommendations. One emerging area of interest is the relationship between cannabis use – specifically tetrahydrocannabinol (THC), its psychoactive component – and stroke outcomes. This article examines the evidence surrounding THC after stroke, focusing on functional outcomes, mortality risk and potential biological mechanisms.
Cannabis and stroke: The clinical study
According to one study, young cannabis consumers seem to be at a higher risk of developing long-term disabilities following a stroke.
Published in the journal Stroke, researchers reviewed the medical records of 1,014 patients who had been hospitalized with an aneurysmal sub-arachnoid hemorrhage (aSAH), a type of stroke that involves a bleed on the brain. Forty-six of these patients had tested positive for THC.
After comparing the outcomes of the cannabis-positive patients with the others, the researchers found that the patients who had tested positive for THC were 2.8 times more likely to have a long-term moderate-to-severe physical disability following their stroke.
More concerningly, the patients were also 2.2 times more likely to die after their stroke than the cannabis-sober patients.
Due to the nature of the study, this positive relationship between cannabis and worse stroke outcomes was only observed, not clinically proven. To properly determine if THC can worsen the impacts of a stroke, the authors of the paper plan to conduct a follow-up lab study.
To get their findings, the researchers reviewed the data of 1,014 aSAH patients who had been treated at the Barrow Neurological Institute in Phoenix, Arizona, from August 1, 2007, to July 31, 2019. Forty-six of these patients (4.5 percent) had tested positive for THC.
Following their stroke, half of all patients (50.2 percent) were considered to have a “poor functional outcome,” 36.2 percent of patients suffered from delayed cerebral ischemia (poor blood flow in the brain) and 13.5 percent died.
The researchers found that 52.2 percent of THC-positive patients suffered a delayed cerebral ischemia (DCI), compared to 35.4 percent of the other patients. Cocaine, methamphetamine and tobacco, on the other hand, were not associated with a higher risk of DCI.
Overall, THC-positive stroke patients were 2.7 times more likely to have a DCI, 2.8 times more likely to have a long-term disability and 2.2 times more likely to die.
Credit: iStock.
“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 T. Lawton, a senior author of the study and president of the Barrow Neurological Institute, said in a statement.
While Lawton and his colleagues note that their study has its limitations – the small sample size of cannabis users, a lack of information on their frequency and dosing of THC, etc. – they say that the observed association between cannabis use and stroke outcomes is still significant.
Possible biological mechanisms
As to what could be causing the association, the researchers’ paper highlights a few possible explanations from previous studies. According to one paper, THC may directly increase a person’s vulnerability to a stroke by altering the brain’s maximal oxidative capacity. The compound has also been shown to induce cerebral vasoconstriction and multifocal angiopathy (when small blood vessels burst).
Several hypotheses have been proposed:
Vascular effects of THC
- Cerebral vasoconstriction: THC has been shown to narrow blood vessels, which can compromise blood flow.
- Multifocal angiopathy: Damage to small vessels can increase susceptibility to rupture.
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Oxidative stress
- THC may alter oxidative capacity in the brain, making neurons more vulnerable to ischemic damage.
- Increased free radical production could exacerbate tissue injury.
Inflammatory pathways
- Endocannabinoid system modulation may influence neuroinflammation, potentially worsening outcomes in the context of hemorrhage.
These mechanisms highlight why THC stroke outcomes may differ from those of non-users. But to truly determine if and how THC affects stroke outcomes, the researchers behind the study say a double-blind, placebo-controlled, randomized controlled trial will be needed.
THC after stroke: Conflicting research
While the authors of the Stroke paper highlighted a few studies that demonstrated a link between strokes and cannabis use, other studies have come to different conclusions.
One observational study published in 2020 found that marijuana-consuming patients were no more likely to have a stroke than those who didn’t use the drug. In that study, the researchers sifted through data of 9,350 patients who were admitted to the University of Mississippi Medical Center with a stroke.
Of those who tested positive for cannabis, 8 percent had experienced a stroke. Of those who tested negative, 16 percent had experienced a stroke – double the rate of those who consumed cannabis.
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“While more research is needed with larger numbers of people, our study lends support to the studies showing that cannabis use does not increase the risk of stroke,” Carmela V San Luis, a neurology researcher at the University of Mississippi in Jackson, said in a statement at the time.
Much like Lawton, San Luis remarked that more thorough investigative studies will be needed before a firm conclusion can be made about whether THC increases the chances of having a stroke or not.
“Our research adds to the list of studies with conflicting results, so it is important to continue to investigate stroke risk and cannabis use,” San Luis said at the time.
“Future studies are now needed in larger groups of people that not only include data from drug screenings but also dosing amounts as well as a person’s history of cannabis use.”
To clarify whether THC worsens stroke outcomes, researchers recommend:
- Randomized controlled trials: Double-blind, placebo-controlled studies.
- Laboratory models: Animal studies to investigate mechanistic pathways.
- Advanced imaging: Tools such as functional MRI or PET to track cerebral blood flow changes.
- Biochemical assays: Measuring oxidative stress markers, inflammatory mediators and endothelial function.
The relationship between cannabis use and stroke outcomes remains complex and unresolved. Current data suggest that THC exposure may predispose patients to poorer functional recovery and increased mortality after aneurysmal subarachnoid hemorrhage. However, conflicting evidence from other cohorts emphasizes the need for rigorous mechanistic studies and clinical trials. For laboratory professionals, the study of THC after stroke represents an intersection of neuroscience, vascular biology, and cannabinoid pharmacology, offering opportunities to advance understanding of both stroke pathology and the effects of cannabis on brain health.
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