Cannabis and Heart Attack/Stroke Risk: A 183-Million-Patient Meta-Analysis Finds Stroke Risk but Not Heart Attack Risk | Research

The takeaway

In the largest meta-analysis to date, cannabis use was significantly associated with increased stroke risk but not heart attack risk — though the overall cardiovascular evidence remains mixed.

Read this if you use cannabis and have cardiovascular risk factors — the stroke finding is worth discussing with your doctor, even though causation isn't established.

What the researchers found

As cannabis legalization expands globally, the cardiovascular safety question becomes increasingly urgent. Does cannabis use increase the risk of heart attacks and strokes? This meta-analysis pulled together 20 observational studies encompassing over 183 million patients to find out.

The headline findings split in two directions. For acute myocardial infarction (heart attack), cannabis use was not significantly associated with increased risk — the pooled odds ratio was 1.29 but the confidence interval crossed 1.0, meaning the association wasn't statistically reliable. For stroke, however, the picture was different: cannabis use was significantly associated with increased risk.

The magnitude and clinical significance of the stroke finding deserve careful interpretation. Observational studies can't prove causation — cannabis users may differ from non-users in ways that independently affect stroke risk (smoking tobacco, other substance use, socioeconomic factors). The researchers used standard methods to assess and control for confounding, but residual confounding is always a concern with observational data.

The overall prevalence of cannabis use in this massive dataset was 1.9%, and the median follow-up was 6.2 years. The male predominance in the sample (23.7%) likely reflects the demographics of cardiovascular events rather than cannabis use patterns.

This meta-analysis lands in a contentious space. Some prior studies have suggested cannabis increases cardiovascular risk, while others found no association. This analysis, by virtue of its massive sample size, provides the most statistically powered answer to date — and it suggests the risk is real for stroke but uncertain for heart attack.

Why it matters

This is the largest meta-analysis of cannabis and cardiovascular risk ever conducted. With over 183 million patients, it has statistical power that individual studies lack. The finding that stroke risk is elevated while heart attack risk is not suggests cannabis may affect the cardiovascular system in specific ways — possibly through effects on blood vessel function, blood pressure regulation, or clotting — rather than through a general increase in cardiovascular disease.

The numbers in context

20 studies, 183,410,651 patients. Cannabis use prevalence: 1.9%. Median age: 42.4 years. Median follow-up: 6.2 years. Acute MI: pooled OR 1.29 (95% CI crossing 1.0, not significant). Stroke: significantly associated with cannabis use (pooled OR reported as significant). 23.7% male in the overall sample.

How the study worked

Systematic review and meta-analysis of 20 observational studies including 183,410,651 patients. Searched PubMed, Scopus, and Cochrane Library databases. Data on effect estimates combined via random-effects meta-analysis using the DerSimonian and Laird method with generic inverse-variance strategy. Outcomes: acute myocardial infarction and stroke.

Who was studied

20 studies (N=183,410,651 patients, 23.7% male, median age 42.4 years, median follow-up 6.2 years)

What this study cannot tell us

All included studies were observational — the association between cannabis and stroke cannot be confirmed as causal. Residual confounding is a major concern: cannabis users may differ from non-users in smoking habits, other drug use, and socioeconomic factors that independently affect cardiovascular risk. The definition of 'cannabis use' varied across studies (current vs. ever, frequency, route of administration). The very low proportion of males (23.7%) in the overall sample is unusual and may reflect specific study populations. Publication bias is possible.

How to read the evidence

Meta-analysis of observational studies represents strong evidence for an association, but cannot establish causation. The massive sample size gives statistical power, but the observational nature of all included studies means confounding cannot be fully ruled out.

When this study was published

Published in 2023. As cannabis use patterns change with legalization, newer studies may provide updated risk estimates.

The bigger picture

Cardiovascular safety is one of the most important outstanding questions in cannabis research, especially as use increases among middle-aged and older adults. This meta-analysis provides the strongest evidence to date that stroke risk warrants attention, while partially alleviating heart attack concerns. For the RethinkTHC database, this connects to the broader harm-reduction narrative — legalization brings both increased access and a need for better safety data.

Replication

Not stated in abstract.

Funding

Not reported in abstract.

Conflicts of interest

Not reported in abstract.

Questions still open

Is the stroke association driven by smoked cannabis (combustion products) rather than cannabis itself? Does frequency or duration of cannabis use affect stroke risk in a dose-dependent manner? Are specific populations (elderly, those with pre-existing cardiovascular disease) at higher risk? Would non-smoked cannabis (edibles, tinctures) show the same stroke association?

Read the original research

Cannabis and adverse cardiovascular events: A systematic review and meta-analysis of observational studies

Toxicology Reports, 10, 537-543

Toxicology Reports is a peer-reviewed journal focusing on the effects of toxic substances.

View on PubMed ↗Publisher’s paper ↗

Citation

Theerasuwipakorn, Nonthikorn; et al.. (2023). Cannabis and adverse cardiovascular events: A systematic review and meta-analysis of observational studies. Toxicology Reports, 10, 537-543. https://doi.org/10.1016/j.toxrep.2023.04.011