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If the anemia is not due to iron deficiency, taking iron pills will not relieve the anemia and could cause poisoning (iron toxicity). It could also cause an iron overload condition called hemochromatosis, especially in people who have a genetic tendency toward storing too much iron in their bodies.

In some people, iron pills cause stomach discomfort, nausea, diarrhea, constipation, and black stool. Iron is best absorbed if taken on an empty stomach. But if you are having stomach problems, you may need to take the pills with food. Do not take iron pills with milk, caffeinated drinks, or antacids. If the side effects of your iron pills make you feel too sick, talk to your doctor. He or she may know of another type of iron pill you can take.

Iron supplement shots can cause side effects. Shots given in a vein (intravenously, IV) pose the risk of an allergic reaction. Shots given in the muscle of the buttock (intramuscularly, IM) may produce permanent marks on the skin that look like a tattoo.