What Should You Know About Oreos and Black Stool?

Oreos can temporarily darken stool, but truly black, tarry or sticky stool may signal digestive bleeding and needs prompt medical assessment. Food colouring can change stool colour without causing illness; the appearance, smell, persistence and your other symptoms help guide what to do.

A dark biscuit or other strongly coloured food may leave stool dark brown or nearly black for a short time. Iron tablets and medicines containing bismuth can also darken bowel movements. This colour change is different from melaena, which is often jet black, sticky or tar-like and may have a strong, unusual odour. Melaena can happen when blood is digested higher in the stomach or small intestine. Possible causes include gastritis, a peptic ulcer or Helicobacter pylori infection.

A black stool by itself cannot identify the cause. Note whether the colour started after eating Oreos or taking a new medicine, and whether it returns to your usual colour. Do not stop a prescribed medicine without checking with the prescriber.

If the stool was dark after Oreos and you feel well, observe the next bowel movements and avoid assuming that every dark stool is bleeding. Keep a note of foods, supplements and medicines that might affect colour. If the stool remains black, becomes tarry, or you are unsure whether it is food-related, contact a clinician promptly. They may ask about medicines, examine you and arrange tests to check for blood or digestive causes.

Seek emergency help now for black tarry stool with vomiting blood or material that looks like coffee grounds, fainting, severe weakness, confusion, shortness of breath, chest discomfort or severe abdominal pain. These can accompany significant bleeding. Urgent assessment is also appropriate if black stool keeps occurring, even without pain, because digestive bleeding is not always felt.

You could ask: Could my stool colour be related to food, iron or bismuth? Does its texture suggest melaena? Do my medicines increase bleeding risk? What examination or stool testing is needed? Which changes should make me seek emergency help? Bring a list of medicines and supplements, plus when the colour change began and any accompanying symptoms.