Do Iron Supplements Cause Stomach Pain and Bloating?


Iron supplements are known to cause a variety of potential side effects, especially if you consume too much.

Stomach pain and bloating are not the most common, but are sometimes reported.

We’ll look at some data from research showing how common different side effects from iron supplements are, as well as which types of iron supplements are less likely to cause stomach issues.

Is Stomach Pain a Common Side Effect of Iron Supplementation?

The most common adverse effects from taking iron supplements that are reported in research are (12):

  • Abdominal discomfort (i.e. stomach pain, bloating)
  • Nausea
  • Heartburn
  • Constipation
  • Diarrhea

The more iron from a supplement that someone consumes, the more severe the symptoms typically are.

To get a general sense of how common these are, we can look at a specific study that recorded the number of side effect events, shown in the table below (2).

adverse effects reported from iron supplementation

As you can see, the most common side effects, from most to least frequent were:

  • Headache (34 events)
  • Nausea (20 events)
  • Abdominal pain (12 events)
  • Upper respiratory tract infection (9 events)

In total, abdominal pain was reported by 9 subjects, or about 15% of people. So it’s relatively common, but far from everyone experiences it as a result of iron supplementation.


General abdominal pain, which includes issues like stomach pain, bloating, and gas, is a well-established side effect of taking iron supplements for some people.

Certain Types of Iron Supplements Are More Likely to Cause Stomach Issues

Not all iron supplements are created equally.

Some are absorbed poorly, which leads to more digestive stress and a greater risk of stomach problems.

To get a sense for this, consider the results from a comparison study of 2 forms of iron (3):

  • About 21% of patients that received iron sulfate (a.k.a. ferrous sulfate) withdrew due to stomach problems.
  • Only 5% of patients that received iron sucrose (the type given in IV injections) withdrew.

It was a small study, but shows that the type of iron supplemented can have a big impact.

There are 4 common forms of iron in commercial supplements these days of varying quality:

  • Ferric iron – Absorbs the worst.
  • Ferrous iron (e.g. ferrous sulfate) – Absorbs relatively poorly.
  • Carbonyl iron – Absorbs well (4).
  • Chelated iron – Absorbs well (5).

Both carbonyl iron and chelated iron supplements absorb well and are less likely to cause stomach pain and related side effects.

What to Do If Iron Supplements Give You Stomach Issues

Iron supplements are often necessary to treat certain conditions like iron deficiency anemia.

However, aside from side effects like stomach pain and bloating, iron supplements can also be dangerous. Getting too much iron at once can lead to iron toxicity, and taking iron supplements long-term could lead to chronic inflammation (6).

That’s why it’s important to consult your doctor before taking iron supplements. While many other over the counter nutrient supplements are very safe in most situations, iron is not one of them.

If you’re taking iron supplements under the direction of a doctor and are having stomach problems, tell your doctor. You can likely try a different form of iron, or even get an iron injection periodically if all else fails.

About the author

Dale Cudmore

Your friendly neighborhood vegan from Toronto. I've spent over 6 years as a freelance nutrition writer and researcher. During this time, I've tested over 50 vegan protein powders, and over 100 other types of vegan supplements.

Add comment