What herbal supplements can cause heart block?

Herbal Supplements That Can Cause Heart Block

Several herbal supplements can cause heart block, with toad venom, foxglove, licorice, and ephedra being the most dangerous and well-documented culprits. 1

High-Risk Herbal Supplements

Toad Venom

• Contains cardiac glycoside-like compounds similar to digoxin
• Produces toxicity resembling digoxin overdose
• Can cause severe heart block and other arrhythmias
• Digoxin-specific antibodies may reverse toxicity in severe cases 1

Foxglove Tea

• Contains natural cardiac glycosides
• Produces effects similar to digoxin toxicity
• Can cause various degrees of heart block
• Often found in traditional herbal preparations 1

Licorice

• Can cause severe electrolyte disturbances (particularly hypokalemia)
• May lead to heart block through electrolyte abnormalities
• Mimics hyperaldosteronism
• Risk increases with higher doses and prolonged use 1

Ephedra/Ma Huang

• Contains ephedrine alkaloids
• Associated with various arrhythmias including heart block
• Banned by FDA but still found in some supplements
• Particularly dangerous in patients with underlying cardiac conditions 1, 2

Other Concerning Herbal Supplements

St. John's Wort

• Can reduce serum levels of digoxin and warfarin
• May indirectly contribute to heart block by interfering with cardiac medication levels 1

Ginkgo Biloba, Garlic, Ginger, and Ginseng

• Can alter bleeding time
• Should not be used with warfarin
• May complicate management of patients with cardiac conditions requiring anticoagulation 1

Mechanisms of Herb-Induced Heart Block

1. Direct cardiotoxicity: Some herbs contain compounds that directly affect cardiac conduction tissue
2. Electrolyte disturbances: Herbs that cause significant electrolyte abnormalities can disrupt cardiac conduction
3. Drug interactions: Herbs that interact with cardiac medications may precipitate heart block
4. Contamination/adulteration: Some "herbal" products contain undisclosed pharmaceutical agents 3, 4

Risk Factors for Herb-Induced Heart Block

• Pre-existing cardiac disease
• Concurrent use of cardiac medications (especially antiarrhythmics)
• Electrolyte abnormalities
• Renal or hepatic impairment
• Advanced age
• Higher doses of herbal supplements

Clinical Approach to Suspected Herb-Induced Heart Block

1. Immediately discontinue all herbal supplements
2. Obtain detailed supplement history: Brand names, dosages, duration of use
3. Check serum electrolytes: Particularly potassium, magnesium, calcium
4. Monitor cardiac rhythm: Continuous telemetry for unstable patients
5. Consider specific antidotes: Digoxin-specific antibodies for suspected cardiac glycoside toxicity
6. Manage according to degree of heart block: Temporary pacing may be required for high-grade blocks

Prevention Strategies

• Routinely ask patients about herbal supplement use
• Educate patients about potential cardiac risks of herbal products
• Advise against using supplements containing ephedra, toad venom, foxglove, or high-dose licorice
• Recommend patients disclose all supplement use before starting cardiac medications

Common Pitfalls

• Failing to recognize herbal supplements as potential causes of heart block
• Not asking specifically about "natural" or "alternative" remedies
• Assuming herbal products are safe because they are "natural"
• Overlooking potential herb-drug interactions with cardiac medications
• Not recognizing that some banned substances (like ephedra) may still be present in supplements

Clinicians should maintain a high index of suspicion for herbal supplement use in any patient presenting with unexplained heart block, as many patients do not voluntarily disclose supplement use unless specifically asked.