How long can I wait with black stools to see if it goes away without seeing a doctor?

GI Bleeding? Black stools can be caused by harmless things such as certain foods (e.g., blueberries, black licorice) or meds such as bismuth (pepto-bismol) or iron supplements. But it may be a sign of bleeding somewhere in your digestive tract, which can be serious (and doesn't always cause pain). If you haven't eaten these foods/meds & you're having black stools, or if you have vomiting or pain, see your dr.