Iron Supplements: Side Effects, Uses, and More

An Essential Mineral Used to Treat Anemia

Iron supplements, also known as "iron pills," are commonly used to prevent and treat anemia. Anemia is a condition characterized by the lack of healthy red blood cells or hemoglobin.

Women of childbearing age, premature infants, young children, and people with chronic conditions are at greater risk of anemia.

Iron supplements are sold over-the-counter or by prescription. Common iron supplement side effects include constipation, diarrhea, dark stools, and a metallic taste in your mouth.

This article discusses iron supplements and how to use them. It also details iron supplement side effects and how to manage constipation and stomach upset from taking iron pills.

What Is Iron?

Iron plays a key role in making red blood cells that transport oxygen molecules throughout the body. Iron is also needed to metabolize the nutrients we eat and convert them into energy. Moreover, it contributes to the transmission of nerve signals to and from the brain.

While you will generally get enough iron from the foods you eat, there may be times when you may experience an iron deficiency. This commonly occurs during pregnancy or heavy menstruation.

Certain age groups and chronic illnesses can increase your iron deficiency risk. These include:

Iron supplements are also commonly prescribed to women of childbearing age to help prevent anemia.

Health Benefits

Iron supplements are used to treat iron deficiency and iron deficiency anemia. They are not typically used to treat other types of anemia (such as vitamin-deficiency anemia, hemolytic anemia, aplastic anemia, or anemia of chronic disease) unless iron deficiency is diagnosed. The response to oral iron supplements can vary by the underlying cause.

Iron Deficiency

Iron deficiency, also known as sideropenia, is the state in which your body lacks the iron needed to maintain normal function. Iron deficiency is common in the developing world, where more than a quarter of the population may be affected (mostly due to poverty and the lack of nutrition). While this is less common in the United States, it still does occur.

Iron deficiency can also occur due to physiological changes that leave you at a deficit. Iron deficiency can occur in children, for example, because their bodies grow so quickly. Starting in adolescence, a woman's iron need will increase due to her monthly menstrual cycle.

Whatever the cause, iron deficiency can lead to iron-deficiency anemia if left untreated. Iron supplements may not only be used to treat a deficiency but to prevent it from occurring in the first place.

Iron supplements are often provided to people at high risk of a deficiency. These include pregnant women, people on dialysis, or those with inflammatory bowel disease or thyroid disease.

Doing so can help prevent or treat many of the common symptoms of iron deficiency, including:

  • Fatigue
  • Weakness
  • Dizziness
  • Rapid heartbeat
  • Pale skin
  • Hair loss
  • Brittle or grooved nails
  • Sores at the corner of the mouth
  • Sore tongue
  • Twitches
  • Irritability
  • Frequent infections
  • Restless leg syndrome

Iron-Deficiency Anemia

When used to treat iron-deficiency anemia, iron supplements are sometimes effective and well-tolerated and, in other cases not.

According to a 2015 review of studies in the American Journal of Medicine, as many as 27% with people with iron-deficiency anemia will not respond to oral iron supplements.

Generally speaking, women with postpartum anemia respond best. Those with heavy menstrual bleeding or individuals with gastrointestinal-induced anemia tend to be moderate responders. All other cases are largely hit or miss in their response.

If iron supplements are unable to provide relief, intravenous (IV) iron therapy or a blood transfusion may be needed.

iron supplement side effects
Verywell / JR Bee

Iron Supplement Side Effects

Iron supplements are generally safe and well-tolerated if taken at the recommended dose. The most common iron supplement side effect is an upset stomach. This includes:

  • Black, green, or dark stools
  • Bloating
  • Constipation
  • Diarrhea
  • Gas
  • Nausea
  • Stomach cramps
  • Vomiting

Other potential side effects of iron supplements include:

  • Backache
  • Chest pain 
  • Chills
  • Cramps
  • Dizziness
  • Fainting
  • Flushing or red skin
  • Groin pain
  • Headache
  • Hives
  • Metallic taste
  • Muscle soreness
  • Numbness, pain, or tingling of hands or feet
  • Overall feeling of weakness
  • Rapid heart rate
  • Skin rash
  • Teeth staining (from liquid iron)

In rare cases, a serious allergic reaction to iron supplements can occur. Seek immediate medical care if you experience a possible anaphylactic reaction to iron. Warning signs of anaphylaxis include:

  • Hives
  • Itching
  • Rash
  • Red, swollen, blistered, or peeling skin 
  • Swelling of the mouth, face, lips, tongue, or throat
  • Tightness in the chest or throat
  • Trouble breathing, swallowing, or talking
  • Unusual hoarseness
  • Wheezing

Gastric bleeding can also occur while taking iron supplements. Call your doctor if you have any of the following: 

  • Black tar-like or bloody stools
  • Fever
  • Vomiting blood or what looks like coffee grounds

Managing Side Effects of Iron Supplements

Side effects from iron supplements can make it difficult for some people to comply with treatment. Avoid taking iron pills on an empty stomach, which increases the risk of gastrointestinal side effects. To reduce the risk of side effects, start with a lower dose and gradually increase the dose as tolerated.

Try the following tips to prevent and manage stomach upset while taking iron supplements:

  • Drink plenty of water to prevent constipation
  • Eat more vegetables and fiber-rich foods to prevent or treat constipation
  • Take a stool softener to treat constipation
  • Take with food to minimize or prevent stomach discomfort

Iron Overload

Taking too much iron can lead to iron overload. Extra iron in your blood can be toxic to the liver, heart, and pancreas and may cause damage to the joints, as well.

Excessive doses of iron can lead to iron poisoning. Even a single high dose (60 milligrams per kilogram of body weight or more) can lead to death. Iron poisoning symptoms usually become apparent within six to 24 hours of a dose.

Signs of iron poisoning include:

  • Abdominal pain
  • Bloody vomit or stools
  • Excessive diarrhea
  • Severe vomiting

Contact your healthcare provider if you have iron overload or iron poisoning symptoms.

Drug Interactions

Taking iron supplements containing 25 milligrams or more of elemental iron can affect the absorption of zinc and lead to a zinc deficiency. (Elemental iron is not the same thing as the iron supplement dose. Check the product label or speak with your pharmacist who can show you the difference.)

Iron supplements may also interact with the following drugs:

In some cases, separating the doses by two hours may be all that is needed to avoid interactions. In other cases, a dose adjustment may be needed. Speak with your healthcare provider if you intend to use iron supplements and take these or any other chronic medication.

Dosage and Preparation

Iron supplements come in three main forms. Ferrous sulfate is the most common. Other chemical compounds include ferrous gluconate and ferrous fumarate. Iron supplements are sold as tablets, capsules, and liquid.

The dose can vary based on the level of your deficiency as well as the underlying cause. Your healthcare provider will recommend a dose based largely on the Recommended Dietary Allowance (RDA) for iron for your age, sex, and pregnancy status, as follows:

  • Birth to six months: 0.27 mg
  • Seven to 12 months: 11 mg
  • One to three years: 7 mg
  • Four to eight years: 10 mg
  • Nine to 14 years: 8 mg
  • Boys 14 to 18 years: 11 mg
  • Girls 14 to 18: 15 mg
  • Men 19 to 50: 8 mg
  • Women 19 to 50: 18 mg
  • Pregnant women 14 to 18: 27 mg
  • Breastfeeding women 14 to 18: 10 mg
  • Pregnant women 19 to 50: 27 mg
  • Breastfeeding women 19 to 50: 9 mg

Drink a full glass of water or orange juice with each dose. The vitamin C in orange juice is said to boost absorption. The water helps disperse the iron for better absorption.

When used to treat iron-deficiency anemia, the duration of therapy may be as long as six months. This requires a commitment on your part. Once started, you would need to continue treatment even if you feel better and no longer have symptoms.

What to Look For

Vitamin and mineral supplements are not subject to rigorous testing in the United States and can vary from one brand to the next.

To ensure quality and safety, opt for supplements that have been tested and approved by an independent certifying body like the U.S. Pharmacopeia (USP), ConsumerLab, or NSF International.

Iron supplements can degrade when exposed to excessive temperatures and UV radiation. To avoid this, keep the supplements in their original light-resistance container and store them in a dry, cool room. Always check the use-by date and discard any expired, discolored, or damaged supplements.

Frequently Asked Questions

  • Should iron supplements be taken at a certain time of day?

    No, but iron is best absorbed when taken on an empty stomach. However, iron can be rough on your gastrointestinal tract and some people need to take it with a small amount of food.

    To improve absorption, take iron along with foods rich in vitamin C, such as citrus fruits or juice. Avoid taking iron supplements at the same time as high-fiber foods or caffeine, which can hinder absorption.

  • How quickly do iron supplements correct a deficiency?

    Iron supplements start to absorb into the body immediately—especially when taken on an empty or near-empty stomach. Most iron-deficient people start to feel better within a few days.

    However, it can take four to six months of daily iron supplements to fully resolve a case of iron deficiency anemia.

  • What foods are high in iron?

    Most people do not need iron supplements if they maintain a healthy, balanced diet. Rather than reaching for a pill, start by adding iron-rich foods to your meal plan, the highest of which include:

    • Iron-fortified breakfast cereals: 18 mg per cup
    • Oysters: 8 mg per 3-ounce serving
    • White beans (canned): 8 mg per cup
    • Dark chocolate: 7 mg per 3-ounce serving
    • Beef liver: 5 mg per 3-ounce serving
    • Lentils (cooked): 3 mg per ½ cup serving
    • Spinach (cooked): 3 mg per ½ cup serving
    • Tofu: 3 mg per ½ cup serving
    • Kidney beans (canned): 2 mg per ½ cup serving
    • Canned sardines in oil: 2 mg per ½ cup serving
    • Chickpeas (canned): 2 mg per ½ cup serving
    • Stewed tomatoes: 2 mg per ½ cup serving
    • Braised bottom round beef: 2 mg per 3-ounce serving
    • Baked potatoes: 1 mg per medium-sized potato
    • Cashews: 1 mg per 1-ounce serving
    • Green beans (cooked): 1 mg per ½ cup serving
    • Roast chicken: 1 mg per 3-ounce serving
10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  4. MedlinePlus. Taking iron supplements.

  5. Mayo Clinic. Iron supplement (oral route, parenteral route): Side effects.

  6. Memorial Sloan Kettering Cancer Center. Ferrous Sulfate.

  7. Abbaspour N, Hurrell R, Kelishadi R. Review on iron and its importance for human health. J Res Med Sci. 2014;19(2):164-74.

  8. Manoguerra AS, Erdman AR, Booze LL, et al. Iron ingestion: an evidence-based consensus guideline for out-of-hospital management. Clin Toxicol (Phila). 2005;43(6):553-70.

  9. Lynch SR, Cook JD. Interaction of vitamin C and iron. Ann N Y Acad Sci. 1980;355:32-44. doi:10.1111/j.1749-6632.1980.tb21325.x

  10. Michigan Medicine. Iron deficiency anemia.

Additional Reading

By Tracee Cornforth
Tracee Cornforth is a freelance writer who covers menstruation, menstrual disorders, and other women's health issues.