Table 5.

Common Herb-Drug Interactions

Herb	Drug or Drug Class	Interaction or Other Comments
Comfrey	Phenobarbital	Increases metabolism of comfrey, producing a lethal metabolite from pyrrolizidine that results in severe hepatotoxicity
Danshen	Anticoagulants or antiplatelets	Increases bleeding due to additive effects
	Digoxin	Increases side effects of digoxin
Echinacea	Amiodarone or ibutilide	Increases QT interval
	Statins, fibrates, niacin	Increases risk of hepatotoxic effects
Ephedra	Antidiabetes drugs	Increases blood glucose; Decreases effectiveness of oral hypoglycemic agents
	Class IA and class III antiarrhythmics	Increases QT interval
	β-Blockers	Decreases effects of β-blockers, leading to hypertension and tachycardia
	Monoamine oxidase inhibitors	Hypertension
Evening primrose oil	Phenobarbital	Decreases seizure threshold
Garlic	Aspirin, clopidogrel, warfarin, or heparinoids	Increases bleeding risk
Ginkgo biloba	Antidiabetes drugs	Increases hypoglycemia
	Aspirin	Increases bleeding; inhibits PAF hemorrhage
	Warfarin
Ginseng	Antidiabetes drugs	Increases hypoglycemia
	Digoxin	Interferes with digoxin assay, leading to falsely increased levels
	Warfarin	Decreases effectiveness of warfarin
	Phenelzine sulfate	Headache; Irritability; Insomnia
Hawthorn	Digoxin	Increases effects of digoxin
	Calcium channel blockers or nitrates	Increases coronary vasodilatory effects
Kava	Alprazolam	Increases CNS depression; Increases effects of alcohol
Licorice	Spironolactone	Increases effects of spironolactone
Saw palmetto	Anticoagulants or antiplatelets	Increases bleeding
Soy milk	Warfarin	Decreases effectiveness of warfarin
St. John’s wort	Digoxin	Decreases serum digoxin concentration
	Clopidogrel	Increases activity of clopidogrel; Increases bleeding
	Warfarin	Decreases warfarin bioavailability and effectiveness
	Simvastatin	Decreases effectiveness of simvastatin
	Paroxetine	Nausea; Lethargy; Incoherence
	Class IA and III antiarrhythmic agents	Decreases effectiveness (precipitating arrhythmias)
	Cyclosporine	Decreases cyclosporine concentration due to increased clearance (transplant rejection)
	Theophylline	Decreases serum concentration
	Indinavir	Decreases serum concentration (treatment failure in HIV patients)
Yohimbine	Clonidine	Decreases blood pressure reduction effect of centrally active agents
	Guanabenz
	CNS stimulants (eg, amphetamines)	Risk of hypertensive crisis due to its monoamine oxidase inhibitor activity
	ACE inhibitors	Decreases effectiveness of ACE inhibitors; Hypertension
	β-Blockers	Decreases effectiveness of β-blockers; Hypertension; Increases heart rate

Abbreviations: ACE, angiotensin-converting enzyme; CNS, central nervous system; HIV, human immunodeficiency virus; PAF, platelet-activating factor.