Iron tablets commonly cause diarrhoea because iron irritates your digestive tract

Yes, iron tablets frequently cause diarrhoea, and this is one of the most common side effects people experience when taking them. Iron is a mineral your body needs, but when you take it as a supplement in tablet form, it passes through your stomach and intestines in a concentrated dose. This irritates the lining of your digestive tract, which can trigger loose stools or diarrhoea within hours or days of starting the tablets.

The effect varies by person. Some people notice diarrhoea when ready; others develop it after a few days. The amount of iron in each tablet, the type of iron compound used, and your individual sensitivity all play a role in how severe the diarrhoea becomes. Iron supplements can also cause constipation in some people instead, which makes the digestive side effects unpredictable.

Key Takeaways

  • Iron tablets irritate your digestive tract lining, which commonly causes diarrhoea within hours or days of starting them.
  • Taking iron with food, splitting your dose into smaller amounts throughout the day, or switching to a different iron compound can reduce diarrhoea.
  • Diarrhoea from iron tablets usually improves after your body adjusts over one to two weeks, even if you keep taking the same dose.
  • If diarrhoea is severe or does not improve after two weeks, contact your doctor about switching to a different iron product or dose.
  • Drinking extra water and eating fibre-rich foods can help manage loose stools while your body adjusts to the iron.

How iron irritates your digestive system

Iron is chemically reactive and can damage the cells lining your stomach and intestines. When you swallow an iron tablet, it dissolves in your stomach acid and releases iron ions that come into direct contact with your gut lining. This irritation triggers inflammation and speeds up the movement of food and waste through your intestines, which is why you get loose stools.

The effect is dose-dependent: higher doses of iron cause more irritation. A 325 mg ferrous sulphate tablet (which contains about 65 mg of elemental iron) is more likely to cause diarrhoea than a 150 mg tablet. Your stomach acid also plays a role—people with low stomach acid or those taking acid-reducing medications may absorb iron differently and experience different side effects.

Taking iron with food to reduce diarrhoea

Eating food when you take your iron tablet is the simplest way to reduce diarrhoea. Food in your stomach slows down how fast the iron tablet dissolves and moves through your digestive tract, which means less concentrated irritation of your gut lining. This also reduces the amount of iron your body absorbs in one go.

Take your iron tablet with a meal or snack, ideally something containing protein or fat—eggs, yoghurt, bread with butter, or a handful of nuts all work well. Avoid taking iron with tea, coffee, or calcium-rich foods like milk or cheese, because these can block iron absorption. If you have been taking your iron on an empty stomach and experiencing diarrhoea, switching to taking it with food often stops the problem within a few days.

Splitting your dose into smaller amounts

Instead of taking one full iron tablet once a day, ask your doctor whether you can split the dose and take half a tablet twice a day, or a quarter tablet four times a day. Smaller doses spread throughout the day mean less iron hits your digestive tract at once, which reduces irritation and diarrhoea.

This approach works because your intestines can handle smaller amounts of iron without triggering the same inflammatory response. You will still absorb the same total amount of iron over the course of the day, but your gut will tolerate it better. Some people find that taking iron every other day instead of daily also reduces diarrhoea while still building up iron stores over time.

Switching to a different type of iron supplement

Not all iron tablets are the same. Different iron compounds irritate your gut differently, and switching types can stop diarrhoea even if you keep taking the same dose. Ferrous sulphate is cheap and commonly prescribed but causes the most digestive upset. Ferrous gluconate and ferrous fumarate are gentler on the stomach for many people. Iron polysaccharide complexes are absorbed more slowly and cause less irritation.

Your doctor can prescribe a different iron compound if your current tablet is causing severe diarrhoea. Some people tolerate liquid iron supplements better than tablets because you can take smaller sips throughout the day. Delayed-release iron tablets, which dissolve further down in your intestines rather than in your stomach, also cause less diarrhoea for some people, though they may not absorb as well.

How long diarrhoea lasts and when it improves

Diarrhoea from iron tablets often improves on its own after one to two weeks as your digestive system adjusts to the iron. Your gut lining becomes less sensitive, and your body learns to handle the iron without triggering inflammation. This means you may not need to stop taking the iron or change your dose—you just need to wait.

During this adjustment period, drink extra water to replace fluids lost through loose stools, and eat foods high in fibre like oats, beans, and vegetables to help firm up your stools. If diarrhoea is severe enough that you are losing a lot of fluid or electrolytes, or if it does not improve after two weeks, contact your doctor. They can adjust your dose, switch you to a different iron compound, or investigate whether something else is causing the diarrhoea.

Other digestive side effects from iron tablets

Diarrhoea is not the only digestive problem iron tablets cause. Some people experience nausea, stomach cramps, or a metallic taste in their mouth. Others get constipation instead of diarrhoea, which can be equally uncomfortable. These side effects usually fade as your body adjusts, but they can be severe enough that people stop taking their iron tablets early.

If you experience severe nausea or stomach pain alongside diarrhoea, tell your doctor before making any changes to your dose. In rare cases, iron tablets can cause more serious digestive problems, especially if you have an underlying condition like inflammatory bowel disease or irritable bowel syndrome. Your doctor may recommend a different way to get iron, such as iron injections or dietary changes, if tablets are not tolerable.

Frequently Asked Questions

How long does iron tablet diarrhoea last?

Most people find that diarrhoea improves within one to two weeks as their body adjusts to the iron. If it continues beyond two weeks or gets worse, contact your doctor about changing your dose or switching to a different iron compound.

Can I stop taking iron tablets if they give me diarrhoea?

Do not stop without talking to your doctor first. If you have iron deficiency anaemia, stopping iron tablets means your anaemia will not improve. Your doctor can help you find a dose or type of iron that your body tolerates better.

Does taking iron with orange juice help with diarrhoea?

Orange juice helps your body absorb iron because of its vitamin C content, but it does not reduce diarrhoea. In fact, taking iron with acidic juice on an empty stomach may make diarrhoea worse. Take your iron with food instead.

Will iron tablets always give me diarrhoea?

Not necessarily. Some people never develop diarrhoea from iron tablets, while others do only at higher doses. If you have had diarrhoea from one type of iron tablet, switching to a different compound or taking a smaller dose may solve the problem.

Is it safe to take anti-diarrhoea medicine with iron tablets?

Ask your doctor before taking any anti-diarrhoea medication alongside iron tablets. Some anti-diarrhoea drugs can reduce how much iron your body absorbs, which defeats the purpose of taking the iron in the first place.