The Cleveland Clinic suggests that when taking warfarin one should not drink more than "one beer, 6 oz of wine, or one shot of alcohol per day".Warfarin also interacts with many herbs and spices, some used in food (such as ginger and garlic) and others used purely for medicinal purposes (such as ginseng and Ginkgo biloba). All may increase bleeding and bruising in people taking warfarin; similar effects have been reported with borage (starflower) oil. St. Johns wort, sometimes recommended to help with mild to moderate depression, reduces the effectiveness of a given dose of warfarin; it induces the enzymes that break down warfarin in the body, causing a reduced anticoagulant effect.Between 2003 and 2004, the UK Committee on Safety of Medicines received several reports of increased INR and risk of haemorrhage in people taking warfarin and cranberry juice. Data establishing a causal relationship are still lacking, and a 2006 review found no cases of this interaction reported to the USFDA; nevertheless, several authors have recommended that both doctors and patients be made aware of its possibility. The mechanism behind the interaction is still unclear. Chemistry
X-ray crystallographic studies of warfarin show that it exists in tautomeric form, as the cyclic hemiketal, which is formed from the 4-hydroxycoumarin and the ketone in the 3-position substituent. However, the existence of many 4-hydroxycoumadin anticoagulants (for example phenprocoumon) that possess no ketone group in the 3-substituent to form such a structure, suggests that the hemiketal must tautomerise to the 4-hydroxy form in order for warfarin to be active.
Historical information on warfarin from the Wisconsin Alumni Research Foundation
CDC – NIOSH Pocket Guide to Chemical Hazards
Warfarin in the Pesticide Properties DataBase (PPDB)