Less commonly, an underlying disease process, such as an inability of the blood to clot, may contribute to the bleeding. Inability of the blood to clot is most often due to blood-thinning drugs such as warfarin (Coumadin) or aspirin. Liver disease can also interfere with blood clotting. Abnormal blood vessels or cancers in the nose are rare causes of nosebleeds. High blood pressure may contribute to bleeding but is almost never the only reason for a nosebleed