Can Iron Supplements Cause Diarrhea?

Iron supplements can produce gastrointestinal side effects, including diarrhea. If you have diarrhea, abdominal pain or other gastrointestinal symptoms and you're taking iron supplements, consult your health-care provider to make sure that you're taking the correct amount of iron to meet your nutritional needs. Bloody diarrhea, which may be a sign that you've taken too much iron, requires immediate medical attention.

The wrong dose of iron supplements may result in gastrointestinal symptoms. (Image: AndreyPopov/iStock/Getty Images)

Side Effects

Iron transports oxygen in your red blood cells and participates in your body's production of energy. If you're at risk for iron deficiency due to pregnancy, inadequate iron in your diet, iron deficiency anemia, a bleeding disorder or another health condition, your health-care provider may recommend iron supplements to help you meet your requirements for this essential nutrient. The most common side effects of iron supplements involve the gastrointestinal system, according to the University of Maryland Medical Center. Diarrhea, nausea, heartburn, abdominal pain and constipation are among the side effects of iron supplements. Oral iron supplements may cause black stools, which may be mistaken for a sign of gastrointestinal bleeding. Black stools, which occur when your body breaks down the iron in your supplements, are a harmless side effect.


Because of the health risks of taking excessive amounts of iron, you should not take more than the recommended dietary allowance, or RDA, for iron without medical supervision. For women between the ages of 19 and 50, the RDA for iron is 18 mg per day. Pregnant women require 27 mg per day. Breastfeeding women over age 19 require 9 mg per day. These groups are at risk for iron loss due to menstruation and childbearing. Men ages 19 and older and women over age 50 require 8 mg of iron each day. If you've been diagnosed with iron deficiency anemia or another health condition that requires iron supplementation, you may require more than the RDA.

Iron Overload

When you exceed your nutritional requirements for iron, your body stores excess amounts of this element in your muscles, bone marrow, liver and spleen. Taking iron supplements over a long period may lead to iron toxicity. Early symptoms of iron toxicity include weakness, fatigue, abdominal pain and joint pain. In the later stages, iron overload may cause serious health complications, including damage to your heart and liver, diabetes and arthritis. To avoid taking too much supplemental iron, follow your health-care provider's recommendations for the amount of iron you should consume each day.


The tolerable upper intake level for iron, or the amount most people can take safely each day, is 45 mg. Taking excessive amounts of iron – 50 to 100 times the RDA – may destroy gastrointestinal cells, causing vomiting and bloody diarrhea. An overdose of iron supplements may be fatal. Eating food with iron supplements may help prevent nausea, diarrhea or other gastrointestinal side effects. However, taking iron supplements with milk products, cereal, coffee or tea may reduce the amount of iron that your body absorbs. If you aren't experiencing gastrointestinal side effects, take iron supplements on an empty stomach to ensure adequate absorption, MedlinePlus advises.

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