Constipated? You May Want to Cool It on This Supplement

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On August 31, 2025

Problems pooping? Believe it or not, the culprit behind your constipation may be lurking in your daily multivitamin or dietary supplement.

Getting your iron this way may be backing you up in the bathroom. And while iron is a super important mineral for our bodies (we need it to make hemoglobin, a protein in red blood cells that helps blood carry oxygen throughout the body), some of us may be taking too much.

Here’s what you should know about iron supplements and constipation.

So, Why Does Iron Make You Constipated?

Constipation is a common side effect of iron supplements, per the U.S. National Library of Medicine, because iron can be tough on the digestive tract. These supplements can cause diarrhea for some people, and sometimes nausea and vomiting, too.

Studies have shown that taking an iron supplement affects our gut microbiota, promoting the presence of potentially harmful bacteria, which may result in gas, bloating and constipation, according to a February 2015 meta-analysis published in PLOS One.

The researchers behind that study also hypothesized that iron causes oxidative damage to the intestines, leading to inflammation and subsequent gastrointestinal discomfort.

Do You Even Need to Take an Iron Supplement?

Most Americans get enough iron by eating a variety of foods, according to the National Institutes of Health (NIH). That’s because iron is naturally found in meat, beans, leafy greens and nuts as well as fortified cereals and breads, explains Lee Ann Chen, MD, a gastroenterologist at NYU Langone Health.

That said, how much iron your body requires is heavily dependent on your age, sex and health status, says Dr. Chen, who adds that adults should not take more than 45 milligrams of elemental iron a day.

Indeed, the recommended dietary allowance (RDA) for iron is only 18 milligrams for people assigned female at birth between the ages of 19 and 50 and a mere 8 milligrams for people assigned male at birth, per the NIH.

If you’re a vegetarian, the RDA is almost twice as high, because iron from plant-based foods (called nonheme iron) is less bioavailable — meaning less readily absorbed — than the kind found in meat (heme iron).

Though most people get enough iron from their diets, certain groups of people may have trouble getting adequate amounts.

“Anyone with known iron-deficiency anemia, people with heavy periods and pregnant people need more iron,” Dr. Chen says. Frequent blood donors and individuals with cancer, gastrointestinal disorders or heart failure are also more likely to have iron deficiency, per the NIH.

For these people, taking a daily iron supplement may be necessary. However, the NIH points out that iron-only supplements usually contain way more than you need, with many delivering as much as 65 milligrams or 360 percent of your daily value.

If you have a health condition or are concerned about your iron levels, talk to your doctor about whether an iron supplement is right for you, and which kind of supplement you should take.

How Can You Relieve Constipation When Taking an Iron Supplement?

If you must take a daily multivitamin or dietary supplement containing iron, there are a few things you can do to combat getting clogged up.

First, try simple, standard constipation treatments such as increasing your water and fiber intake and being more active, suggests Dr. Chen. Exercising is a tried-and-true, natural way to stimulate a bowel movement. Certain yoga poses — that involve twisting and forward bends — are particularly helpful for promoting poop.

“If needed, short-term use of osmotic laxatives (e.g. Miralax) can also be effective to soften the stool,” Dr. Chen says.

But if these methods aren’t enough to get things flowing, you can also try to change the way you’re obtaining your iron. For example, some individuals get their iron infused. Taking your iron intravenously doesn’t cause constipation, but this procedure has its own potential side effects, says Dr. Chen, who recommends less-invasive approaches.

“Some people find it better to take their iron every other day or switch to a liquid formulation so they can more easily [adjust] the dose to the one that is more tolerable,” she says.

You may also consider using “slow-release” or “enteric-coated” iron supplements to reduce GI discomfort, but keep in mind that these forms decrease the amount of iron your body absorbs, says Dr. Chen, who stresses that you should only make these kind of changes with your doctor’s consent.