From Constipation to Taste Changes: 6 Iron Supplement Side Effects, and How to Manage Them

GoodRx Health

Iron deficiency (low iron levels) is the most common cause of anemia (a low level of red blood cells). Iron deficiency anemia can happen to anyone who doesn't consume enough iron from their diet. But it's more common if you're pregnant, menstruating, or following a meat-free diet.

Iron supplements can help replenish your body's iron stores to treat anemia. You can find them over the counter (OTC) in several forms, such as ferrous sulfate, ferrous gluconate, and ferrous fumarate. If you're taking an iron supplement, it's helpful to know what side effects to expect.

Iron supplement side effects at a glance

Below is a list of common and rare iron supplement side effects.

Common iron supplement side effects include:

• Nausea and vomiting

• Constipation

• Diarrhea

• Stomach pain

• Heartburn

• Metallic taste

• Changes in stool color

• Gas

• Stained teeth

Rare but serious iron supplement side effects include:

• Stomach damage

• Organ failure (due to iron overdose)

Let's look more closely at six possible iron supplement side effects and how to manage them.

Good to know: This article covers the side effects of oral iron supplements. But there are also several prescription iron infusions, which are given through a vein by a healthcare professional. Your prescriber can review the side effects of iron infusions with you before your first treatment.

1. Nausea

Nausea is one of the most common side effects of iron supplements. It's best to take iron on an empty stomach. But if your nausea is bothersome, it's OK to take iron supplements with a small amount of food. Just be sure to avoid dairy products, caffeine, and high-fiber foods (such as whole grains or raw vegetables). These can affect how iron is absorbed if they're taken together. Breaking your daily dose into two smaller doses may also help lessen your nausea.

The most common forms of iron (ferrous sulfate and ferrous gluconate) are called iron salts. Iron salts are more likely to cause nausea and other stomach-related side effects than other forms of iron.

Chelated iron products (such as ferrous bisglycinate) and heme iron polypeptide are examples of iron products that may be easier to tolerate. Extended-release ferrous sulfate may also be easier on your stomach than other iron salts. Your pharmacist can help you find an iron product that's gentler on your stomach, if needed.

2. Constipation

Constipation is also very common with iron supplements.

Staying hydrated, exercising, and getting enough fiber in your diet can help prevent and manage constipation. If those don't work, consider adding an OTC stool softener, such as docusate sodium (Colace).

If your constipation persists, it's time to talk to a healthcare professional about next steps. If left untreated, constipation can become a more serious issue. Seek emergency care if you have constipation along with severe stomach pain, vomiting, or rectal bleeding.

3. Diarrhea

While some people become constipated from iron supplements, others may experience diarrhea.

If you have diarrhea, be sure to drink plenty of fluids to prevent dehydration. It's also best to avoid fried or greasy foods, caffeinated drinks, and alcohol. If needed, an OTC anti-diarrhea medication such as loperamide (Imodium A-D) may help. But if your diarrhea lasts more than a few days, talk to a healthcare professional. They can recommend a different dosage or type of iron supplement to improve your symptoms.

Seek medical care right away if your diarrhea is accompanied by severe abdominal pain or a fever. These could be signs of a more serious issue.

4. Metallic taste

Iron is a form of metal, so it's fairly common to get a metallic taste in your mouth after taking an iron supplement. For some people, the taste from iron supplements can be bad enough that they avoid taking them.

Chewing sugar-free gum or rinsing your mouth with mouthwash after taking iron can help cover up the metallic taste. You can also talk to a pharmacist about a different form of iron that's less likely to have this side effect.

5. Change in stool color

Iron supplements may make your stool appear dark green or black. This can be alarming, but it's typically not a serious issue.

In rare cases, iron supplements may cause stomach damage that leads to bleeding (more on that next). And black, tarry stool can also be a sign of bleeding. So it's a good idea to report any change in your stool to a healthcare professional if you're unsure about what's causing it.

6. Stomach damage

As mentioned, iron supplements may cause nausea and heartburn for some people. If these symptoms are left untreated, iron supplements may damage the lining of your stomach over time, which may lead to an ulcer. So it's best to manage stomach-related symptoms as soon as they appear.

The most common symptom of a stomach ulcer is a burning pain in your upper abdomen. This pain is often worse when you have an empty stomach and improves after you eat. Bleeding from an ulcer can also cause black, tarry stools. Let your prescriber know if you're experiencing these symptoms.

Stomach damage from iron supplements isn't common. But it's more likely if you take more iron than recommended. In severe cases, you may vomit blood or have bright red blood in your stool when this happens. Seek emergency care if you or a loved one takes more iron than recommended or any of these symptoms appear.

Do iron supplements cause weight gain?

No. Iron supplements don't seem to cause weight gain on their own.

Anemia may reduce your appetite. So if you're taking iron to treat anemia, your appetite may improve, leading to an increase in your body weight. But other research suggests that treating iron deficiency anemia may in fact help with weight loss.

Talk to your prescriber if you notice any bothersome changes in your weight while taking iron. They can determine the cause and best course of action.

How do you know if you're taking too much iron?

You should only take an iron supplement if a healthcare provider recommends it. Taking too much iron can raise your risk of stomach-related side effects. In large doses, it can cause liver problems, organ failure, and even death.

The recommended daily iron dosage is based on elemental iron. And each type of iron supplement contains a different amount of elemental iron, so the daily dosage will be different among different products. If your prescriber recommends an iron supplement, they'll help you understand what to look for on the "Supplement Facts" label of the iron product you're taking to determine your dose.

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