If a blood test shows your iron is low during pregnancy, your provider will likely recommend an iron supplement on top of your prenatal vitamin. Iron pills work, but they have a reputation for upsetting stomachs. This guide covers the types, the side effects, and what you can ask your provider when iron is hard to take.

The short version

  • Most women get enough from a prenatal vitamin, which usually has about 27 milligrams (mg) of iron. Extra iron is for women who test low.
  • Read the “elemental iron” amount on the label. That’s the iron you actually get.
  • Common side effects are nausea and constipation, especially at 45 mg a day or more. Ask your provider about a different form or schedule rather than stopping.
  • Space it out. Take iron apart from calcium supplements, and at least 4 hours apart from thyroid medicine.
  • If pills don’t work, iron given through an IV is an option.
  • Keep iron locked away from children. Accidental overdose is a leading cause of fatal poisoning in children under 6.

Do you need one?

It depends on your blood tests, not on how tired you feel.

  • If your iron is normal, your prenatal vitamin is usually enough. The benefits of extra iron when you aren’t low are uncertain, and some studies link it to problems such as gestational diabetes, according to the NIH.
  • If you have iron-deficiency anemia, the American College of Obstetricians and Gynecologists (ACOG) recommends iron supplements in addition to your prenatal vitamin. Your provider will choose the dose, which may be higher than the usual 45 mg upper limit for a while.
  • If you’re vegetarian or vegan, ask whether you need extra iron even before a test shows you’re low.

Our article on iron levels in pregnancy explains the tests.

Types of iron and how to read the label

Iron supplements come as different iron “salts.” Each contains a different share of usable iron, called elemental iron. The NIH gives these figures for the most common forms:

Form on the label Share that is elemental iron
Ferrous fumarate 33%
Ferrous sulfate 20%
Ferrous gluconate 12%

You don’t have to do the math. The Supplement Facts panel lists the elemental iron, which is the number to compare. For example, a ferrous sulfate tablet might say 325 mg on the front but list about 65 mg of iron in the Supplement Facts.

Ferrous versus ferric. Ferrous forms are absorbed better than ferric forms (such as ferric citrate). Other forms, including heme iron polypeptide, carbonyl iron, iron amino-acid chelates, and polysaccharide-iron complex, might cause fewer stomach side effects, according to the NIH. They’re worth asking about if a standard iron pill bothers you.

Side effects and how to make iron easier to take

The most common side effects are stomach-related. Doses of 45 mg a day or more can cause nausea and constipation, and larger doses can also cause stomach pain and vomiting, especially when iron is taken without food, according to the NIH.

If iron is bothering you, don’t quietly stop. Tell your doctor or midwife and ask about:

  • Taking it with food. Side effects are more likely on an empty stomach. Ask whether taking it with a meal makes sense for you.
  • A different form. Some forms, listed above, may be easier on the stomach.
  • A different dose or schedule. The World Health Organization notes that a once-weekly dose can be used when daily iron causes side effects that are too hard to tolerate, in settings where anemia is less common, according to the NIH. Your provider can tell you whether an adjusted schedule fits your situation.
  • Your other symptoms. Pregnancy itself can cause nausea and constipation, so it helps your provider to know what was going on before you started iron.

If you’re dealing with morning sickness at the same time, our article on vitamin B6 for morning sickness may help.

Medicines and nutrients that interact with iron

Tell your provider and pharmacist about everything you take. These interactions come from the NIH:

  • Calcium supplements may lower iron absorption. Take them at a different time of day.
  • Thyroid medicine (levothyroxine). Iron can make it work less well. Labels advise taking levothyroxine at least 4 hours apart from iron.
  • Acid reducers such as omeprazole and lansoprazole lower stomach acid, which helps absorb iron. People who are iron deficient and take them may respond less well to iron pills.
  • Zinc. Iron supplements with 25 mg or more of iron can lower zinc absorption.
  • Levodopa, used for Parkinson’s disease and restless legs syndrome, is absorbed less well when taken with iron.

When pills aren’t enough: IV iron

Iron pills are the first treatment for iron-deficiency anemia, but they don’t always work or aren’t always tolerated. The International Federation of Gynecology and Obstetrics says that if iron-deficiency anemia is found at the start of the third trimester, iron given through an IV (intravenous iron) should be considered, according to the NIH. That timing matters because there’s less time left for pills to work before delivery.

If your levels aren’t improving, or you can’t keep iron pills down, ask your provider whether IV iron is an option for you.

Keep iron away from children

Iron is one of the most dangerous things in a medicine cabinet for a small child. Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6, according to the NIH. Child-resistant packaging and warning labels have greatly reduced these poisonings, but only when they’re used.

  • Keep iron pills and prenatal vitamins in their original child-resistant bottles, closed tightly.
  • Store them up high and out of sight, not on the kitchen counter or in a purse.
  • If a child swallows iron pills, call Poison Help at 1-800-222-1222 or a doctor right away, even if the child seems fine.

What to do now

  • Check your iron supplement’s Supplement Facts panel for the elemental iron amount.
  • Space iron apart from calcium supplements and, if you take it, thyroid medicine.
  • If iron upsets your stomach, call your provider about a different form or schedule instead of stopping.
  • Move all iron-containing pills out of children’s reach today.

Related reading

Sources

Updated October 2026. This article is for general information and is not a substitute for advice from your health care provider.