Possible Interaction: Warfarin and Garlic

“The case reports with severe adverse effects such as spontaneous postoperative …, thrombosis, subarachnoid hemorrhage and/or subdural hematomas after concomitant use of warfarin and the medicinal herbs: Panax ginseng, Hypericum …, Serenoa repens, Angelica sinensis, Vaccinium species, Allium sativum , Zingiber officinale, Tanacetum parthenium, Lucium barbarum, … Camellia sinensis have been estimated.”

“For example, garlic has been shown to increase the clotting time and international normalized ratio (INR) of warfarin , cause hypoglycaemia when taken with chlorpropamide, and reduce the area under the plasma concentration-time curve (AUC) and maximum concentration of saquinavir in humans.”

“Potential risks of bleeding due to the use of Ginkgo biloba, garlic or ginseng with aspirin or warfarin was the most reported herb–drug interaction.”

“The herbs that showed the greatest potential to interact with warfarin include garlic , ginger, ginkgo, St. John's wort, and ginseng, i.e. plants normally consumed as food and also used for therapeutic purposes.”

“ Garlic (Allium sativum) interacts with chlorpropamide, fluindione, ritonavir and warfarin ; it also reduces plasma concentrations of chlorzoxazone (a CYP2E1 probe).”

“It has been suggested that herbal medicines such as garlic , either as a dietary supplement or in cooking, may also interact with warfarin , resulting in poor international normalised ratio (INR) control.”

“ Garlic also has numerous drug interactions, notably with warfarin , but also others.”

“Finally, garlic may enhance the pharmacological effect of anticoagulants (e. g. warfarin , fluindione) and reduce the efficacy of anti-AIDS drugs (i. e. saquinavir).”

“The adverse haematological effects of the herb were originally linked to the simultaneous ingestion of aspirin or other blood diluents, and the interaction … of the platelet-activating factor (PAF) by ginkgolide B was pointed out; a similar PAF action occurs with other herbal remedies, such as garlic , when … warfarin.”

“Two of the commonest prescribed medicines, aspirin and warfarin can cause such spontaneous bleeding when taken in conjunction with Ginkgo biloba, ginseng (Panax ginseng), feverfew, ginger and garlic , all of which have some anticoagulant and/or antiplatelet activity.”

“ Allium sativum (garlic) changes the pharmacokinetics of paracetamol and warfarin and the effects of chlorpropamide.”