Hi, Thanks for your question. There is a noted drug interaction with Viagra (generic name sildenafil) and warfarin in certain patients. In patients who have pulmonary hypertension, there is an increased risk of bleeding when taking these medications together. This risk is most likely caused by the high dose of Viagra used to treat the pulmonary hypertension (about 2-3 times higher dose than used to treat erectile dysfunction). If you have pulmonary hypertension, you should be sure to discuss with your doctor the risks and benefits of taking these medications together. If you do not have pulmonary hypertension, there is no documented drug interaction between Viagra and warfarin. If you would like to learn more about these medications, you can read about Viagra here and warfarin here. Best of luck, Casey