Can Iron Supplements Cause Headaches? (+How to Prevent)


There are many situations where taking an iron supplement is good for your health.

But there can be side effects, including headaches.

We’re going to take a quick look at what side effects from iron supplements are possible, how common they are, and which types of iron are more likely to cause them than others.

Common Side Effects from Iron Supplements

There’s a good amount of research available about iron supplements.

One study was primarily looking at the effect of consuming iron capsules at different intervals, but also tracked adverse effects of the subjects. The chart below shows the number of side effects in the different trials:

adverse effects reported from iron supplementation

In case you can’t see, overall there were 75 adverse effects among 60 people. Obviously one subject could report multiple instances of an adverse effect, but it shows they’re fairly common overall.

Most importantly, we can see that headaches were a common complaint, making up 34 of the 75 reports (about 45% of side effect events).

Note that all these reports were mild, so severe headaches, nausea, or abdominal pain is not common with iron supplements. 


Iron supplements often cause side effects, especially in high doses. The most common side effects are nausea, abdominal pain, and headaches.

Side Effects From Non-Heme Iron vs Heme Iron

Iron in food comes in 2 main forms: heme (animal) and non-heme (plant).

Non-heme iron doesn’t absorb nearly as well, which is why vegans often need to get extra iron, or even take a supplement.

One research study found something interesting:

The frequency of constipation and the total incidence of all side effects were significantly higher for non-heme iron when compared with the heme iron-non-heme iron combination and a placebo. 

The group in their study that took an iron supplement with both heme and non-heme iron had fewer side effects.

However, it’s not too common to find supplements that mix those 2 types in practice, so this may push someone towards a heme iron pill.

Unfortunately, we don’t know exactly why this is. The obvious guess is that since non-heme iron doesn’t absorb as well, more of it needs to be handled by your digestive system, which adds more strain.

If that’s the case, then improving the absorption of a non-heme iron supplement may reduce the chances of symptoms like headaches and stomach problems.

There are 2 main ways of doing that:


Heme iron is less likely to cause headaches and other side effects than non-heme iron from plants.

Which Type of Iron Supplement Causes Is Least Likely to Cause Headaches?

There are 4 main types of iron that you’ll find in iron supplements, 2 of them are “good”, and 2 are clearly worse.

Not surprisingly, the cheapest forms of iron are also the worst. Research has shown that they commonly cause side effects. These 2 forms are:

  • Ferric iron – The hardest type to absorb
  • Ferrous iron – While better than ferric iron, still often comes with side effects. You’ll see it labeled as something like ferrous sulfate or ferrous gluconate.

On the other hand, if you look at the top plant-based iron supplements, you’ll see that there are 2 forms of non-heme iron that absorb much better. They cost a bit more but are typically worth it.

Those 2 forms are:

  • Carbonyl iron – Very easy to absorb, making it easy on stomach issues in most cases.
  • Chelated iron –  This form of iron packages iron together with small amino acids, which makes them much more absorbable than the cheaper forms of iron.

While more research is needed, supplements that include carbonyl or chelated iron are probably less likely to induce symptoms like headaches.

Summary: Do Iron Supplements Cause Headaches?

You don’t want to ignore symptoms from iron supplementation, as it can be dangerous.

There are even concerns that long-term iron supplementation can lead to chronic inflammation and serious diseases (source).

So while minor headaches from iron supplementation are relatively common, they could be a sign of something more serious.

If it’s more than a one-time event, you should consult your doctor about your supplementation to be on the safe side or to find a better alternative.

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.

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