Cannabis use linked to 37% higher stroke risk in massive study

Researchers at the University of Cambridge have found that cannabis, cocaine, and amphetamines are associated with a significantly greater risk of stroke, including among younger people. The findings come from an analysis that drew on data involving more than 100 million people.

Stroke remains one of the world's biggest health problems and ranks as the third leading cause of death and disability combined. Many of its major risk factors, however, can be changed through lifestyle choices, including diet, physical activity, and other behaviors.

Recreational drug use is also widespread. In 2024, 8.8% of adults between ages 16 and 59 in England and Wales, representing about 2.9 million people, reported using a legal or illegal recreational drug during the previous year. Recent US data indicate that more than half of people over age 12 have used substances such as cocaine, cannabis, and opiates at least once.

Investigating the Connection Between Drugs and Stroke

Previous research has increasingly suggested that recreational drugs may contribute to stroke risk. Much of that evidence, however, has varied in quality and has been observational. That makes it difficult to determine whether the drugs themselves increase stroke risk or whether the apparent connection reflects other characteristics or behaviors common among people who use them.

To obtain a clearer picture, researchers from the University of Cambridge Department of Clinical Neurosciences conducted a meta-analysis covering studies with more than 100 million participants. Meta-analysis allows scientists to combine and examine data from multiple published cohort studies. By pooling results, researchers can draw stronger conclusions than they might from smaller individual studies, particularly when earlier findings have been inconsistent.

Their results, published in the International Journal of Stroke, showed substantial differences in stroke risk associated with several drugs. Cocaine and amphetamine use were each linked to roughly twice the risk of stroke (cocaine increased the risk by 96%, amphetamines by 122%), while cannabis use was associated with an increase of about 37%. Opioid use, by contrast, showed no statistically significant association with stroke risk.

Stroke Risk Was Especially High in Younger Users

The researchers also examined people under age 55 separately. Within this younger group, amphetamine use was associated with nearly three times the risk of stroke (an increase of 174%). Cannabis was linked to a smaller 14% increase in stroke risk, while cocaine use was associated with a 97% increase.

The team then investigated whether the relationships might go beyond simple associations. They used Mendelian randomization, a statistical method that examines naturally occurring genetic variants connected with risk factors and stroke. Researchers can use these genetic differences to assess whether evidence supports a causal relationship between a particular risk factor and a health outcome.

The genetic analysis found that cocaine use disorders were especially associated with brain hemorrhage and cardioembolic stroke (where a blood clot forms in the heart and travels to the brain, blocking blood flow and leading to damage of brain tissue). Cannabis use disorders were associated with stroke overall and were particularly linked to large artery stroke. According to the researchers, these genetic findings support the possibility of a causal relationship rather than an association alone.

Problematic alcohol use was also associated with an increased risk of cardioembolic stroke and large artery stroke. Alcohol addiction, meanwhile, was linked to a greater overall risk of stroke.

The researchers could not perform the same Mendelian randomization analysis for amphetamine use because sufficiently large genetic datasets containing information about amphetamine use are not currently available.

How Recreational Drugs Could Increase Stroke Risk

Several biological mechanisms could help explain why these substances are associated with stroke. The researchers point to sudden increases in blood pressure, spasms and narrowing of blood vessels, abnormal heart rhythms, greater blood clotting (especially cannabis), and inflammation or vasculitis (especially amphetamines).

All of these processes are already known to contribute to stroke. They can play a role in ischemic strokes, which occur when blood clots interrupt blood flow, as well as hemorrhagic strokes.

Dr. Megan Ritson from the Stroke Research Group at the University of Cambridge said: "This is the most comprehensive analysis ever conducted on recreational drug use and stroke risk and provides compelling evidence that drugs like cocaine, amphetamines, and cannabis are causal risk factors for stroke. These findings give us stronger evidence to guide future research and public health strategies."

Dr. Eric Harshfield, Alzheimer's Society Research Fellow at the Department of Clinical Neurosciences, said: "Our analysis suggests that it is these drugs themselves that increase the risk of stroke, not just other lifestyle factors among users. Taken together, our findings emphasize the importance of public health measures to reduce substance abuse as a way of helping also reduce stroke risk."

Reference:

Megan Ritson, Hugh S Markus, Eric L Harshfield. Does illicit drug use increase stroke risk? A systematic review, meta-analyses, and Mendelian randomization analysis. International Journal of Stroke, 2026; 21 (6): 788 DOI: 10.1177/17474930261418926