Instructed patient in medication Plavix prevent unwanted blood clots that can occur with certain heart or blood vessel conditions. While you take Plavix: you may bruise and bleed more easily, you are more likely to have nose bleeds, and it will take longer for any bleeding to stop. Call your doctor right away if you have any of these signs or symptoms of bleeding: unexpected bleeding or bleeding that lasts a long time, blood in your urine (pink, red or brown urine), red or black stools, bruises that happen without a known cause or get larger cough up blood or blood clots vomit blood or your vomit looks like coffee grounds.