Hi, Champix contains varenicline that belongs to the group of medications known as smoking cessation therapies is used to help smokers quit smoking. Warfarin belongs to the group of medications that is known as anticoagulants or blood thinners is used in the treatment of blood clots like deep vein thrombosis, pulmonary embolism etc., and in the prevention of clots from forming. According to the clinical studies, varenicline like Champix didn t alter the pharmacokinetics of a single dose of Warfarin in patients who were smokers. Even Champix doesn t affect Prothrombin time. But smoking cessation, with or without treatment with Champix, itself may alter the pharmacokinetics or pharmacodynamics of Warfarin, for that dosage adjustment may be required. Without consulting your doctor first, you should not start taking Champix while you are on Warfarin. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician