Bismuth subsalicylate is used to treat diarrhea, nausea, heartburn, indigestion, gas, or upset stomach. You should not use bismuth subsalicylate if you have bleeding problems, a stomach ulcer, blood in your stools, or if you are allergic to aspirin or other salicylates. Do not give this medicine to a child or teenager with a fever, flu symptoms, or chickenpox.