Iron supplements are one of the more risky supplements to take, and should be used with doctor supervision.
They frequently cause side effects, including nausea.
We’ll skim over a few studies that back this up, and also go over other common symptoms of a bad reaction from iron supplements.
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Do Iron Supplements Cause Nausea as a Side Effect?
Even decades ago, the potential side effects of iron supplementation were well-known. They included (1):
- Nausea
- Heartburn
- Diarrhea
- Constipation
- Abdominal pain
- Headaches
One important note is that the more iron is consumed, the more severe symptoms tend to get.
To find out how common nausea is, we can look at a study that recorded adverse events in subjects (2). While they were testing if taking iron supplements at different frequencies mattered (it didn’t), we’re more interested in the side effects they saw, shown in the table below.
In total, there were 75 side effects reported from 60 subjects (one subject could report multiple).
Of those, 10 individuals reported nausea (about 16%), and there were a total of 20 total nausea events (so it was recurring for some people).
One final factor to consider is that certain populations are at more risk than others.
Research showed that nausea is quite common in pregnant and postpartum women when taking iron supplements (3). The number one reason for discontinuing iron supplementation for these women was nausea, which is a big deal if they’re anemic.
While it will depend on the form of the iron supplement, nausea is a relatively common side effect from iron supplements, affecting up to about 16% of people.
Reducing Nausea From Iron Supplementation
The numbers above may have surprised you a bit, but you should also know that our understanding of the chemistry behind supplements has improved greatly over the years.
Most of the supplements used in research, especially older studies, are cheaper forms of iron that don’t absorb well. The 2 main ones that you’ll still see in supplements today are:
- Ferric iron
- Ferrous iron (e.g. ferrous sulfate or iron sulfate)
But there are other forms of iron sold that are much easier to absorb and should in theory cause fewer side effects like nausea and stomach issues. The main 2 that most people should look for are:
- Chelated iron
- Carbonyl iron
Both of these have been shown to absorb quite well (4, 5).
They do cost a bit more, but it’s a relatively low amount when you look at the per serving cost.
If someone has nausea from a particular form of iron, it may be possible to find an alternative that does not give them nausea. Both chelated and carbonyl iron are typically well tolerated.
Plant vs Animal Iron for Nausea
In addition to the form of iron, it can also come in heme or non-heme variants based on if it came from animals or plants.
Plants contain non-heme iron, which doesn’t absorb as well.
A study even found that non-heme iron causes a higher risk of side effects (6).
Sticking to the better forms of iron will go a long way to improving the absorption rate.
In addition, vitamin C greatly enhances the absorption of non-heme iron. That’s why you’ll see vitamin C included in many high quality plant-based iron supplements.
What to Do If Iron Supplements Give You Nausea
Taking iron supplements can be dangerous, as it’s easy to get too much, which can have serious side effects.
There is research that speculates that long-term use of iron supplements could lead to chronic inflammation (7).
The vast majority of people should not be taking iron supplements, especially long-term, without a very good reason.
That’s why iron supplements should be taken with direction from your doctor. This is especially important if you’re experiencing side effects.
