Medically Reviewed

Why Iron Supplements Can Cause Constipation (And How to Help Avoid It)

Iron supplements can help people who need more intake. While iron supplements are often associated with constipation, the form of iron makes a difference.

Iron is found in many foods and is also available as a dietary supplement. It is essential for many functions in the body including maintaining healthy oxygen levels, hormone synthesis, and more. Keep reading to find out why iron supplementation may benefit you and how to help avoid occasional constipation often associated with iron supplementation.

Do Iron Supplements Cause Constipation?

Constipation can be a frequent side effect of oral iron supplements. Some studies suggest that this type of iron can increase the production of methane gas in the gut, which is associated with the potential for constipation. Side effects of iron supplementation may depend on the dosage and form of iron. More absorbable forms of iron usually cause less constipation and gastrointestinal side effects.

Tips to help avoid occasional constipation

To help with constipation from iron supplements, begin taking them in smaller doses and increase gradually over several days until you reach your recommended dosage. Taking iron supplements with a source of vitamin C can also help you to better absorb the iron and reduce the potential for constipation and gastrointestinal upset.

The Care/of Iron Supplement includes calcium and magnesium ascorbate — buffered forms of vitamin C. This highly absorbable form of vitamin C helps the body absorb iron more efficiently in turn.

Tips to help relieve constipation from iron supplements

If you experience constipation from iron supplementation, ask your healthcare provider about reducing your dosage; taking smaller doses spread throughout the day, or taking your original dosage every other day, which may also help alleviate the symptoms of constipation. These are common approaches taken by nutrition professionals to support gastrointestinal comfort during iron supplementation.

While iron is best taken on an empty stomach or in between meals (usually at least 30 minutes before or 2 hours after meals), iron supplements can be taken with a small snack if they cause stomach upset. If your iron supplement is rough on your stomach, you may find that iron bisglycinate is a gentler form.

Combatting Iron Constipation for Different Use Cases

Iron-deficiency anemia

Iron deficiency anemia is a common health issue worldwide and iron supplements are usually the go-to remedy for helping to replenish the body's iron levels. However, they often come with an unpleasant side effect: gastrointestinal discomfort. Some people still experience side effects even when they take lower doses. Food-derived supplements may be gentler on the stomach, especially when paired with absorption-supporting nutrients like vitamin C.


Iron is especially important during pregnancy, which is why the RDA increases from 18 to 27 mg during this time. Up to 52% of pregnant people may experience iron deficiency given the rapid increase of blood volume during gestation. Pregnancy can already exacerbate constipation, and the addition of iron supplements might further worsen symptoms.

To help manage this, pregnant individuals can incorporate several dietary strategies, such as:

  • Eating plenty of raw fruits and vegetables
  • Consuming more fiber, like prunes
  • Increasing intake of whole grains like quinoa, oats, brown rice, and whole wheat
  • Maintaining excellent hydration

If dietary adjustments don’t help, fiber supplements or a stool softener may be worth exploring, but always check with your healthcare provider first.

Heavy menstrual periods

People who regularly menstruate are more likely to need iron support than those who do not, due to the regularly occurring loss of blood. Daily iron supplements can support healthy iron status, energy levels, and the production of healthy red blood cells. However, supplementing with iron is not without its challenges. Taking a daily iron supplement can cause gastrointestinal side effects, even at lower intakes. Intermittent iron supplementation, when guided by a healthcare provider, may be just as beneficial while limiting negative side effects. For menstruation support, they may recommend supplementing with iron the week before and during menstruation or on alternate days throughout the cycle.

Eating plenty of fiber-rich foods, like fruits and vegetables, can help support gastrointestinal transit and reduce iron-caused constipation. It’s important to note that iron supplements should not be taken at the same time as whole grains, calcium, dairy products, zinc, or other minerals, since such combinations can reduce iron absorption.

Vegetarian or vegan diets

Adopting a vegetarian or vegan diet often means you are consuming meals that are naturally higher in fiber. While this has many health benefits, it can present a challenge for iron supplementation. Taking iron with whole grains or high-fiber foods can reduce how well the iron is absorbed in your gut. So, to maximize iron absorption, it’s best to take iron supplements at least 2 hours apart from high-fiber meals.

If you experience gastrointestinal discomfort from iron supplements, consult your healthcare provider. They may recommend a stool softener to alleviate symptoms. Alternatively, they might suggest adjusting your iron intake, possibly by reducing the dose or taking the supplement every other day. This approach can help minimize discomfort, while still supporting healthy iron intake.

Vegetarians and vegans seeking natural sources of iron may also benefit from pea protein. It is an iron-rich option that can be easily integrated into plant-based meals. Care/of’s Plant-Based Protein contains 5 mg of iron per serving and includes pea protein.

Which form of iron is least constipating?

There are various non-heme forms of iron in dietary supplements. Supplement forms include the following:

  • ferrous sulfate (usually in tablet form)
  • ferrous gluconate (usually in liquid form)
  • ferric citrate
  • ferric sulfate
  • ferrous bisglycinate

Note: “ferrous” and “ferric” both refer to iron of varying atomic structures. Ferrous iron is more bioavailable than ferric iron. Studies show that iron bisglycinate is absorbed better and can increase iron levels at smaller doses than the common ferrous sulfate form.

Care/of’s iron supplement contains iron bisglycinate, a chelated form of iron. Chelation helps the mineral from interacting with other compounds, making it easier for the body to digest than non-chelated minerals, thus reducing the risk of constipation.

When Not to Take Iron Supplements

Iron supplements may interact with certain medications and should always be discussed with your prescribing practitioner. Avoid iron supplements if you have excessive levels of iron in your blood. Always get blood levels checked before supplementing with iron. Excessive iron can be dangerous, so speak to your healthcare provider about the appropriate dosage for your needs.

When to Speak to a Healthcare Professional

Talk to your healthcare provider if you experience signs of anemia (including fatigue, weakness, cold hands and feet, and dizziness) or heavy menstrual bleeding, as these may be reasons for needing iron supplementation.

Always get your blood levels of iron checked before beginning an iron supplement.

The Bottom Line

While iron supplements can sometimes cause constipation, the type of iron supplement can make a difference. Iron bisglycinate is well absorbed with fewer side effects reported, and taking a source of vitamin C with your iron supplements can help boost absorption and lessen uncomfortable side effects.

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