What is the most important information I should know about warfarin?

Do not take aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Motrin, Advil, Nuprin, others), ketoprofen (Orudis, Orudis KT, Oruvail), naproxen (Naprosyn, Aleve, Anaprox), and others while taking warfarin, except under the direction of your doctor. These medicines increase the risk of bleeding.
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, and green leafy vegetables (e.g., spinach, Swiss chard, coriander, collards, cabbage). Do not change the amount of these foods in your diet without first talking to your doctor.
It will be necessary to regularly monitor your therapy with a blood test called a "PT" or an "INR." These tests help to determine the amount of warfarin that you need to take.
Contact your doctor if you experience any unusual bruises or heavily bleeding wounds, diarrhea, infection, or fever during treatment with warfarin.