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Side Effects of IRON

Updated on February 2, 2012

Although most individuals consume sufficient iron in their diet, and therefore do NOT need to take extra iron, sometimes a patient will be told by their physician to take an iron supplement.

You may be surprised to know that iron deficiency is actually the leading single-nutrient deficiency in the world.

Dietary Sources of Iron:

Many people wrongly assume that the only dietary sources of iron are red meats. There are, in fact, many other good sources of iron which we can get from food. These include:

  • Eggs (especially the yolk)
  • Whole grains, dried beans and dried fruits
  • Seafood: like salmon, tuna or oysters
  • Iron fortified cereals
  • Dark meat in poultry

These sources of iron are unlikely to cause side effects. However, they will often be insufficient to treat a serious iron deficiency. Therefore, iron supplementation may be necessary. And in such cases, my patients often ask me about IRON SIDE EFFECTS.

In this article I will briefly review the more common side effects from iron, and some things you can do to help prevent (or treat) them.


First, the severity of the side effects associated with iron supplements will often vary based on the amount of ELEMENTAL iron in each tablet. This often confuses people, and we health care providers (and often manufacturers) have often added to the confusion by not being clear.

Iron comes in different forms. For example, there is ferrous sulfate and there is ferrous fumarate and there is ferrous gluconate to name just 3. These various forms of iron have different concentrations of elemental iron. Products with more elemental iron per tablet may cause more side effects for some people. Therefore, although MORE elemental iron may be good to quickly improve your iron levels, LESS iron per tablet may be better to reduce side effects.

LOOK carefully at the iron supplement you purchase and see how much ELEMENTAL iron it contains per tablet. 65mg of elemental iron is A LOT. You might be better off selecting a product with LESS elemental iron and taking it more frequently (say 2 - 3 times daily).


Constipation - This is the most frequent bothersome side effect from iron tablets. Iron causes constipation due to incomplete absorption from the intestines. The iron that does not get absorbed remains in the intestinal tract and causes it to slow down, often resulting in constipation. SOLUTION: Avoid this problem by choosing an iron supplement with LESS elemental iron. Alternatively (or additionally) you may choose to add a stool softener (like docusate sodium). Take 1 stool softener with each iron tablet, up to 3 times daily.

Nausea/Upset Stomach - Probably the second most bothersome complaint with iron is the GI irritation. As iron tablets begin to dissolve in the stomach they can irritate the sensitive lining of our stomach and small intestines causing pain, cramping, nausea or even diarrhea. SOLUTION: One way to reduce this side effect from iron is to take a "time released" version of iron such as Slow-Fe. Time released irons slowly allow the iron to be released and thereby limit the irritation potential. Additionally, although iron is absorbed somewhat better on an empty stomach, it may be best to take iron with food in order to tolerate it.

Darkened stools - A darkening of the stools is a normal side effect from iron supplements. This does not indicate any problem. It is normal, and will stop after your need for iron tablets have ended.

Toxicity - Also known as "iron poisoning." Iron tablets are normally safe. However, in children, too much iron can be VERY dangerous. If you have young children in the house, never leave iron tablets somewhere that they might be accidentally ingested. There have been tragic fatalities associated with as little as 200mg of iron. That is less than 4 tablets! Iron overdose can be treated and should be referred to immediate medical attention if it is suspected.


Okay, so you want to avoid side effects from iron...but you also want to take ENOUGH to actually be effective. So how much do you need?

First, you should check with your doctor and have him/her suggest a dosage based upon the severity of your need.

Next, you will probably need to return to the office (or lab) for additional blood work in 3-4 weeks, to see if your hemoglobin levels have sufficiently improved. Normal hemoglobin levels for adult males are 14-18gm/dl and for females 12-16gm/dl. Ultimately it is the result of these blood tests that will tell you if you need to take more or less iron.

If you have NO recommendation from a physician but were simply told to pick up an "iron supplement" from the pharmacy, then I recommend you consider starting with approximately 50mg of elemental iron daily until you hear otherwise.

This box contains iron with 45mg of Elemental Iron per tablet.
This box contains iron with 45mg of Elemental Iron per tablet.


Reading an Iron Supplement label from the vitamin shelf in the pharmacy can sometimes feel like reading a foreign language.

Why don't they just make it simple???? Oh, that's right. If it were too easy I wouldn't have a job!

For example, on 1 bottle of iron tablets you might find ALL the following information:

  • 325mg Ferrous Sulfate
  • 5GR.
  • 65mg elemental iron.

What? So how much iron is really in there?

  • The 325mg refers to the total amount of "Ferrous Sulfate" which includes both the 'iron' and the 'sulfate' molecules. We really don't care about that.
  • The "5 Gr." is sometimes also included. The "Gr" stands for "Grains." This is an old and outdated system for weights. 1 Grain = about 65mg. So 5 grains is just another way of saying 325mg.
  • The "65mg" is the important number. Usually the package will state this is the amount of "elemental" iron. THAT is what we want to know.

So when reading ANY iron supplement container, just look for the amount of "elemental" iron. This should probably be somewhere between 18mg and 65mg per dose.


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    • pharmacist profile image

      Jason Poquette 5 years ago from Whitinsville, MA

      Um...maybe...but why? Iron tablets will work faster and more cheaply, without adding all that fat to your diet. Just my opinion...

    • profile image

      Ines 5 years ago

      Dear Pharmacist, Do you believe that one can recover from a 30% hematocrit just eating huge amounts of meat and liver? thanks and regards, Ines

    • pharmacist profile image

      Jason Poquette 6 years ago from Whitinsville, MA


      Certain types of iron deficiency are more common in women, and for most of us dietary sources are sufficient. A standard Multivitamin with Iron will not cause problems, but excessive iron intake is not healthy. Thanks!

    • dahoglund profile image

      Don A. Hoglund 6 years ago from Wisconsin Rapids

      I've been led to believe that women need iron supplements more than men and the with men it can build up in the body, therefore I avoid vitamens with iron.

    • pharmacist profile image

      Jason Poquette 6 years ago from Whitinsville, MA


      Thanks for the comment - looks like you have had a very interesting career. Thanks for sharing what you know here on Hubpages!!

    • teaches12345 profile image

      Dianna Mendez 6 years ago

      Thanks for sharing this information on iron and its proper dosage. It is interesting to know that dark meat in poultry contains a good concentration of iron. I will look at my vitamins to see what the mg of iron is in each tablet. Great article!

    • healthwriterbob profile image

      healthwriterbob 6 years ago from United States

      Hi Pharmacist,

      Thanks for a very informative hub. You are right that 65 mg of elemental iron is a lot to take in. A multi-vitamin/mineral supplement contains about 18 mg of iron which is the recommended daily allowance. People who worry that they are not getting enough iron in their diet would probably do well to take one multi-vitamin/mineral pill a day. Voted up, useful, interesting.

    • agreenworld profile image

      Dawn A. Harden 6 years ago from CT-USA

      Excellently written and insightful.

    • Barbara Kay profile image

      Barbara Badder 6 years ago from USA

      This is an excellent article. I am one of those that can't take it.