Green or tarry stools are commonly caused by which of the following?

Green or tarry stools are commonly caused by which of the following?

• A. Iron supplements
• B. Vitamin C
• C. Calcium carbonate
• D. Fiber supplements

Answer: (A)

Stool color changes often reflect what a person takes. Iron supplements frequently darken stool, sometimes giving it a greenish-black, tarry appearance because unabsorbed iron interacts with stool pigments. This change is usually harmless, but it can be mistaken for true tarry stools from GI bleeding, so if someone has other signs of bleeding, further evaluation is needed. The other supplements listed don’t typically produce this dark, tarry coloration: calcium carbonate tends to make stools lighter or chalky, fiber can alter texture or color somewhat but not in a classic tarry way, and vitamin C doesn’t normally cause this level of dark stool color.

Stool color changes often reflect what a person takes. Iron supplements frequently darken stool, sometimes giving it a greenish-black, tarry appearance because unabsorbed iron interacts with stool pigments. This change is usually harmless, but it can be mistaken for true tarry stools from GI bleeding, so if someone has other signs of bleeding, further evaluation is needed. The other supplements listed don’t typically produce this dark, tarry coloration: calcium carbonate tends to make stools lighter or chalky, fiber can alter texture or color somewhat but not in a classic tarry way, and vitamin C doesn’t normally cause this level of dark stool color.