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What Are the Side Effects of Iron Pills?

author image Karla Casco
Karla Casco began writing in 2010, focusing her work on diseases and treatments and their side effects. She has also created patient handouts, PowerPoint presentations and journal clubs. Karla has a doctorate in pharmacy from St. John's University and holds a pharmacy license for the state of New York.
What Are the Side Effects of Iron Pills?
Iron supplements have several common side effects. Photo Credit: HEMARAT/iStock/Getty Images

Physicians prescribe iron supplements for the prevention and treatment of iron-deficiency anemia. There are three types of over-the-counter iron supplements in tablet form: Fergon (ferruous gluconate), Ferro-Sequels (ferrous fumarate) and Feosol (ferrous sulfate). Each contains different amounts of iron. Iron may produce several side effects in the body, and patients should discuss these with a health care professional.

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A common side effect that may occur in individuals on iron is constipation. According to the “Drug Information Handbook,” more than 10 percent of individuals experience constipation while on iron medication. Patients should drink plenty of fluids and obtain an adequate amount of fiber in the diet. Also, patients should exercise regularly and eat balanced meals. If the constipation is persistent or worsens, patients should seek the advice of a health care professional who can recommend something to help.

Gastrointestinal Irritation

Gastrointestinal irritation is also common in users of iron supplements. Stomach cramping or stomach pain may occur; both of these occur in more than 10 percent of patients. If patients experience these effects, they should take the iron tablets with meals. This will usually alleviate these undesired side effects.

Nausea and Vomiting

More than 10 percent of users may experience nausea and vomiting. These effects usually subside when iron is given with a meal rather than on an empty stomach. Patients can also try chewing gum or sucking on hard candy to alleviate the side effects. However, if these side effects worsen or are accompanied by fever, patients should seek medical attention as soon as possible.

Darkening of Stool and Urine

The “Drug Information Handbook” states that over 10 percent of patients using iron supplements will experience darkening of stools. The stool may appear black or dark green; this is a normal side effect when taking iron, and is not a harmful effect. The urine may also appear darker in about 5 percent of individuals. This effect is also harmless. The stool and urine will return back to normal once the medication is stopped.

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  • "Drug Information Handbook, 15th Edition"; Lacy, Charles F., Armstrong, Lora L., et al.; 2007
  • "Pharmacotherapy: A Pathophysiologic Approach"; Dipiro, Joseph T., Talbert, Robert L., et al.; 2008
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