Avoid sudden changes in your diet. Vitamin K decreases the effects of warfarin. Large amounts of vitamin K are found in foods such as liver, broccoli, brussels sprouts, spinach, Swiss chard, coriander, collards, cabbage, and other green leafy vegetables. Do not change the amount of these foods in your diet without first talking to your doctor. • Avoid eating cranberries, drinking cranberry juice, or taking cranberry herbal products. • Avoid drinking alcohol, which can increase some of the side effects of this medication. • Avoid smoking cigarettes or chewing tobacco. Tobacco can alter the effects of warfarin and cause problems with your therapy.