- A contraindication to the use of either warfarin or aspirin, e.g. active peptic ulcer disease, active bleeding diathesis, platelets <100,000*, hematocrit <30, INR >1.3 (if not on warfarin), clotting factor abnormality that increases the risk of bleeding, alcohol or substance abuse, severe gait instability, cerebral hemorrhage, systemic hemorrhage within the past year, severe liver impairment (AST >3x normal*, cirrhosis), any condition requiring regular use of non-steroidal anti-inflammatory agents, allergy to aspirin or warfarin, uncontrolled severe hypertension (systolic pressure >180 mm Hg or diastolic pressure > 110 mm Hg), positive stool guaiac not attributable to hemorrhoids, creatinine >3.0*. *on most recent test done within 30 days prior to randomization