Cannabis May Increase Stroke Risk By 37%, According To The Largest Study Ever Conducted In The World

The largest study ever conducted on cannabis and stroke analyzed over 100 million people and found a worrying fact: the use of the drug was associated with a 37% increase in the risk of stroke. Researchers also used genetic analysis to investigate whether this relationship might be more than a simple coincidence.

Cannabis use has been increasing in several countries, driven by both legalization and the perception that it is a relatively safe drug. However, while its potential therapeutic benefits continue to be studied for some specific diseases, the number of studies investigating its possible negative effects on cardiovascular and brain health is also growing. One of the biggest concerns is stroke, a leading cause of disability and death worldwide.

To better understand this relationship, researchers conducted one of the most comprehensive studies ever published on the subject. First, they performed a systematic review of the scientific literature, gathering all available studies that investigated the association between illicit drugs and stroke risk.

After applying rigorous selection criteria, the scientists included 32 studies conducted in different countries, involving more than 100 million participants. These studies contained information from hospitals, national health databases, and large population surveys, allowing for a much more robust analysis than any single study.

But the researchers went further. They also used a modern technique called Mendelian randomization, considered one of the best tools for investigating possible cause-and-effect relationships when it is not possible to conduct experiments on humans.

Instead of just tracking people's behavior, this technique analyzes small genetic differences inherited at birth that naturally increase the predisposition to the use of or dependence on certain substances.

Because these genetic characteristics are randomly distributed from birth, they help reduce the influence of factors such as income, diet, smoking, access to healthcare, and other habits that could distort the results. In this way, scientists can more confidently assess whether there is a potentially causal relationship between the use of a substance and a particular disease.

The results showed that people who used cannabis had, on average, about a 37% higher risk of suffering a stroke compared to those who did not use the drug. The risk was even higher among cocaine and amphetamine users, practically doubling or even more than doubling in some studies. For opioids, however, the researchers did not find a consistent association.

When they analyzed the genetic data, they again observed signs that a predisposition to cannabis use disorder was related to an increased risk of stroke, especially those caused by the blockage of large arteries that supply the brain.

Although the study did not investigate exactly why this happens, previous research suggests some possible mechanisms. Cannabis can cause changes in blood pressure, modify heart rhythm, promote spasms in blood vessels, and alter blood clotting in some people.

All these factors can increase the likelihood of a stroke, especially in individuals who already have other risk factors, such as hypertension, diabetes, high cholesterol, or smoking. In the case of cocaine and amphetamines, these effects tend to be even more intense, which helps explain the elevated risk observed.

The authors emphasize that the results do not mean that everyone who uses cannabis will suffer a stroke, but they indicate that the risk may be higher than previously thought. As the number of users continues to grow in several countries, understanding these effects becomes an important public health issue.

The researchers argue that doctors and patients should talk openly about these risks, especially among people with a history of cardiovascular disease or other predisposing factors. Furthermore, further research will be important to identify which groups are most vulnerable and how to reduce this risk more effectively.

READ MORE:

Does illicit drug use increase stroke risk? A systematic review, meta-analyses, and Mendelian randomization analysis

Megan Ritson, Hugh S Markus, and Eric L Harshfield

International Journal of Stroke. 09 March 2026. Volume 21, Issue 6DOI: 10.1177/17474930261418926

Abstract: 

Epidemiological evidence suggests associations between substance use disorders and risk of stroke, but whether these are due to confounding or are true causal relationships remains uncertain. To meta-analyze the observational evidence on illicit substance use and stroke risk and apply Mendelian randomization (MR) to evaluate potential causal effects of substance dependence on stroke subtypes. We conducted a systematic review and meta-analysis of studies reporting associations between illicit drug use and stroke (PROSPERO registration—CRD420251053702). The meta-analysis included 32 studies comprising more than 100 million total participants across administrative, hospital-based, and population-based datasets. Pooled odds ratios (ORs) were estimated using multivariate random-effects models for ischemic and hemorrhagic subtypes. We then performed two-sample MR using genome-wide association study summary statistics to examine associations between seven drug exposures and all stroke, ischemic and hemorrhagic stroke, and ischemic stroke subtypes. Meta-analysis demonstrated significant associations of cannabis (OR = 1.37, 95% confidence interval (95% CI) = 1.14–1.65), cocaine (OR = 1.96; 95% CI = 1.27–3.01), and amphetamines (OR = 2.22, 95% CI = 1.40–3.53) with increased stroke risk, while no significant association was observed for opioids. Findings for cannabis showed some heterogeneity and small-study effects. MR analyses revealed that cannabis use disorder was associated with any stroke (OR = 1.11 [1.01–1.51]) and large artery stroke (OR = 1.35, 95% CI = 1.01–1.80), and cocaine dependence was associated with cardioembolic stroke (OR = 1.08, 95% CI = 1.02–1.14) and intracerebral hemorrhage (OR = 1.38, 95% CI = 1.15–1.65). Genetically predicted substance use disorder overall was associated with any stroke (OR = 1.33, 95% CI = 1.02–1.72) and intracerebral hemorrhage (OR = 7.79, 95% CI = 3.46–17.54). Problematic and dependent alcohol use was linked to large artery and cardioembolic stroke, whereas nicotine dependence showed no significant associations. Our findings provide consistent observational and genetic evidence that several forms of substance misuse increase stroke risk, particularly cocaine, amphetamines, and cannabis. These findings suggest important public health implications for prevention strategies targeting substance use disorders to mitigate stroke risk.