High THC Cannabis Use and Atrial Fibrillation Risk
Based on the most recent and highest quality evidence, high THC cannabis use is associated with increased risk of atrial fibrillation through multiple cardiovascular mechanisms, though the absolute risk appears relatively low in the general population. 1
Evidence for Cardiovascular Risk
The American Heart Association clearly documents that marijuana affects heart rhythm through several mechanisms 1:
- Blocks reuptake of catecholamines at presynaptic terminals, causing sympathetic stimulation
- Increases heart rate and blood pressure in a dose-dependent fashion
- Causes coronary vasoconstriction while increasing endothelin-1 and decreasing nitric oxide
- Promotes a prothrombotic state through increased platelet activation and aggregation
Long-term cannabis use is specifically associated with adverse cardiovascular events including arrhythmias, as documented by multiple medical societies 1. The American College of Physicians notes that THC potency has dramatically increased from 9% in 2008 to 17% in 2017, with concentrates reaching up to 70% THC, potentially elevating all health risks including arrhythmias 1.
Mechanisms of Arrhythmia Induction
Cannabis triggers atrial fibrillation through distinct pathophysiological pathways 2:
- Direct electrophysiological effects on cardiac tissue
- Ion channel modulation affecting cardiac conduction
- Calcium handling abnormalities in myocardial cells
- Autonomic tone changes with sympathetic predominance
- Myocardial ischemia from coronary vasoconstriction
- Inflammatory responses affecting atrial tissue
Clinical Evidence and Context
A 2020 systematic review identified atrial fibrillation as one of the most common specific dysrhythmias associated with cannabis use, appearing in 19% of case reports 3. Multiple case reports document new-onset AF in young patients without other risk factors following marijuana smoking 4, 5.
However, the largest prospective cohort study (UK Biobank, n=150,554) found no statistically significant increase in incident AF among occasional users (HR 0.98) or frequent users (HR 1.03) compared to never users after multivariable adjustment 6. This apparent contradiction likely reflects that while cannabis can trigger AF through documented mechanisms, the absolute risk in otherwise healthy individuals remains low.
High-Risk Populations
The risk is substantially elevated in patients with pre-existing cardiovascular vulnerabilities 2:
- Advanced age (>65 years)
- Pre-existing cardiovascular disease
- History of cardiac arrhythmias
- Left atrial enlargement
- Structural heart disease
- Hypertension or heart failure
Combined use of marijuana with tobacco results in greater increases in heart rate and vasoconstriction than either substance alone, according to the American College of Cardiology 1.
Clinical Implications
Cannabis use should be considered as a possible etiology of new-onset AF, especially in relatively young patients with no other predisposing risk factors 4, 5. The European Society of Cardiology recommends considering drug-induced atrial fibrillation in the differential diagnosis of new-onset AF 2.
When cannabis-induced AF is suspected 2:
- Discontinue cannabis use immediately
- Monitor ECG in high-risk patients
- Manage AF according to standard guidelines with rate or rhythm control
- Assess for other reversible causes
Important Caveats
The dose-dependent nature of cannabis cardiovascular effects means higher THC concentrations pose greater risk 1. Most documented cases involve paroxysmal AF that may resolve spontaneously within hours of onset 4, 5.
Clinicians should inquire about acute and chronic cannabis use in patients presenting with tachycardia, dysrhythmia, chest pain, or unexplained syncope 3. Patients who use cannabis should be educated on this association, especially those with underlying cardiac disease or risk factors 3.