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Common foods and drugs that can cause the stool to appear bloody

Red coloration, similar to fresh blood

Certain antibiotics*

Beets

Flavored gelatin (red colored)

Kool-Aid or fruit punch (red colored)

Red licorice

Red-dyed snack foods (eg, spicy "red-hot" snacks)

Black coloration, similar to melena

Bismuth preparations (Pepto-Bismol, Maalox, Kaopectate)

Activated charcoal

Chocolate

Blueberries

Iron supplements^¶

Large quantities of some dark green foods

False-positive results to fecal occult blood test

Rare red meat

Peroxidase-containing vegetables (turnips, horseradish, broccoli, cauliflower, and cantaloupe)

* Several reports have described cases of very red-appearing stools associated with cefdinir, apparently caused by an interaction with iron supplements or iron-containing infant formula.^[1-3] Rifampin can cause orange discoloration of stools as well as urine. Other antibiotics in red vehicles (eg, cherry syrup) may cause a red tint to the stool, especially in infants or others with a fast transit time. Antibiotics can also trigger true gastrointestinal bleeding (Clostridium difficile [C. difficile] colitis). Therefore, red-appearing stools should be evaluated with guaiac or other tests for blood.
¶ Whether iron supplements cause false-positive results for fecal occult blood testing is controversial.

References:

Lancaster J, Sylvia LM, Schainker E. Nonbloody, red stools from coadministration of cefdinir and iron-supplemented infant formulas. Pharmacotherapy 2008; 28:678.
Roath MC, Di Palma JA. Cefdinir and red stool. Gastroenterology and Hepatology 2013; 9:338.
Graves R, Weaver SP. Cefdinir-associated "bloody stools" in an infant. J Am Board Fam Med 2008; 21:246.

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