Genetic analysis found no broad causal link between cannabis use and heart disease, with possible exceptions for small vessel stroke and atrial fibrillation | Research

The takeaway

Mendelian randomization found no causal effect of cannabis use on most cardiovascular diseases, but after adjusting for tobacco and BMI, cannabis showed possible causal links to small vessel stroke and atrial fibrillation.

Cardiologists, cardiovascular epidemiologists, and genetic researchers.

No causal effect on most cardiovascular diseases after genetic analysis

What the researchers found

Standard MR analysis showed no causal effects of cannabis use on coronary artery disease, myocardial infarction, stroke subtypes, atrial fibrillation, or heart failure. However, multivariable MR adjusting for tobacco and BMI suggested causal effects on small vessel stroke (OR 1.17, 95% CI 1.02-1.35) and atrial fibrillation (OR 1.06, 95% CI 1.01-1.10).

Why it matters

While observational studies have linked cannabis to cardiovascular risk, this genetic approach suggests most of that association may be confounded by tobacco use and obesity, with possible independent effects limited to specific conditions.

The numbers in context

Genetic instruments: 10 SNPs. Multivariable MR small vessel stroke OR: 1.17 (95% CI 1.02-1.35, p=0.03). Atrial fibrillation OR: 1.06 (95% CI 1.01-1.10, p=0.01). No significant effects on CAD, MI, other stroke subtypes, or heart failure.

How the study worked

Two-sample Mendelian randomization using 10 SNPs associated with cannabis use as genetic instruments. Summary statistics from GWAS meta-analyses. Sensitivity analyses including multivariable MR adjusting for tobacco use and BMI.

What this study cannot tell us

MR assumptions may not fully hold. Cannabis use SNPs may also influence tobacco use. Effect sizes for SVS and AF were small and borderline significant. Cannot assess dose-response or route of administration.

How to read the evidence

Well-designed Mendelian randomization with sensitivity analyses, though borderline significant results for SVS and AF warrant replication.

When this study was published

Published in 2021.

The bigger picture

These findings suggest the cardiovascular risks commonly attributed to cannabis may largely reflect confounding by co-occurring tobacco use and metabolic factors, an important distinction for risk assessment.

Questions still open

Are the small vessel stroke and AF associations driven by specific components of cannabis (THC vs. CBD)? How does cannabis consumption method affect cardiovascular risk?

Common questions

Does cannabis cause heart disease?

This genetic study found no causal link between cannabis use and most cardiovascular diseases. Small possible effects on small vessel stroke and atrial fibrillation emerged only after adjusting for tobacco and BMI.

Could tobacco use explain the cannabis-heart disease link?

Likely, at least partially. The main MR analysis found no cardiovascular effects, and the small effects that emerged only appeared in models specifically adjusting for tobacco confounding.

Read the original research

Cannabis Use and the Risk of Cardiovascular Diseases: A Mendelian Randomization Study.

Frontiers in cardiovascular medicine, 8, 676850

View on PubMed ↗Publisher’s paper ↗

Citation

Zhao, Jianqiang; Chen, Heng; Zhuo, Chengui; Xia, Shudong. (2021). Cannabis Use and the Risk of Cardiovascular Diseases: A Mendelian Randomization Study.. Frontiers in cardiovascular medicine, 8, 676850. https://doi.org/10.3389/fcvm.2021.676850