Do Iron Pills Make You Gain Weight?


Minerals such as iron are essential for life. Iron is an important component of red blood cells (RBC), which carry oxygen throughout the body. Iron can be obtained from both the food you eat and dietary supplements.

If you do not get enough iron from your diet, you are at risk of developing anaemia, which is a condition caused by being deficient in RBC. 

Side effects of iron supplements can include heartburn, nausea, constipation and yes, weight gain.

Iron pills for iron deficiency

Iron is one of the essential minerals that your body requires to carry out its functions and is often obtained from food. If your diet does not contain enough iron, your doctor may advise you to take ferrous sulphate supplementation. Ferrous sulphate is a common type of iron supplement.

There are many other iron supplements, such as ferrous fumarate, ferric citrate, ferrous gluconate and ferric sulphate. Iron supplements should be taken on an empty stomach and combined with a vitamin C-rich beverage, such as a glass of orange juice or other juice with extra vitamin C; because vitamin C helps your body absorb iron.8

Haemoglobin vs myoglobin

Your body requires iron to produce haemoglobin and myoglobin. Haemoglobin is a protein found inside RBC, which carries oxygen from the lungs to the rest of the body. All of the tissues and organs receive oxygen through your blood with the help of haemoglobin.

Myoglobin is also a protein which is a part of your muscles; it assists in the delivery of oxygen to the muscle cells. Your body can't produce these proteins if you don't have enough iron, which could lead to iron deficiency anaemia.6 Moreover, iron deficiency anaemia is the most common kind of anaemia.

Side effects of iron pills

Iron deficiency anaemia is treated and prevented using the medicine ferrous fumarate, which is a type of iron found in certain foods. Iron supplements are available as tablets, capsules or liquid and are available over the counter and with a prescription. 

Ferrous fumarate can cause side effects in some people, just like any other medicine. Many individuals experience either no adverse effects at all or only mild ones. If you are experiencing any of the following side effects, it is in your best interest to speak with your pharmacist or doctor.3 

  • Nausea or vomiting
  • Stomach discomfort or heartburn
  • Constipation
  • Loss of appetite
  • Diarrhoea
  • Black-stained teeth
  • Dark or black faeces (poo)

If you experience nausea, vomiting or stomach discomfort try to take the iron supplement with or just after a meal.

Levels of haemoglobin and iron return to normal after 2 months of iron therapy in most cases. However, in rare circumstances, it could be necessary to continue taking iron supplements for an additional 6 to 12 months. Your doctor will monitor the amount of iron in your body and decide how long you need to continue taking iron supplements based on the results of routine blood tests.4

Rarer side effects

In rare cases, ferrous fumarate can cause a severe allergic reaction called anaphylaxis.7 In very rare cases, people who take iron supplements may feel weak, have double vision or have throat or chest pain when they swallow.

People who take too much iron may experience the following:

  • Diarrhoea
  • Fever
  • Stomach pain 
  • Nausea

 Late-stage iron overdose symptoms include:

  • Pale and clammy skin
  • Blue-coloured lips and nails
  • Shallow or rapid breathing
  • Unusual weakness 

If you experience any of the above symptoms, you should seek medical help immediately.

Are iron pills related to weight gain?

In 2016, a study found a link between iron supplement intake and weight increase. In this study, 33 patients who were taking iron supplementation were observed for three months. It was revealed that 30 of those individuals gained weight, and the amount of weight gained was related to increased levels of haemoglobin.5 The three individuals who didn't gain weight, they did not show an increase in haemoglobin.  

Although weight gain can be correlated as a side effect of iron supplementation, however, this side effect is not widely reported and more studies need to be conducted to validate this finding.

Causes of anaemia

Iron deficiency is the most common cause of anaemia. It can be caused by either a condition present at birth or a condition you develop through time.

As discussed, anaemia is defined by low haemoglobin levels in the blood, which might happen if:

  • your body is unable to produce enough RBCs.
  • the body can’t replace RBCs at the same rate that they’re being destroyed/lost due to conditions such as heavy periods or pregnancy.

During pregnancy, iron deficiency anaemia is quite common and is typically brought on by an increase in blood requirements and a diet low in iron.2 

In individuals who don’t have periods, the most common cause of iron deficiency anaemia is abnormal stomach and/or intestinal bleeding. This can be brought on by taking non-steroidal anti-inflammatory drugs (NSAIDs), including aspirin and ibuprofen. But, it can also be due to stomach ulcers, inflammation of the bowel or oesophagus (food pipe), haemorrhoids (piles), or stomach or bowel cancer, though these are less common. Any other illnesses or behaviours that cause blood loss could also result in iron deficiency anaemia.1

Symptoms of anaemia

The signs and symptoms of anaemia can vary greatly depending on its cause and severity. It is possible that you will not experience any signs or symptoms of anaemia.2 

If signs and symptoms do arise, they may include:

  • Fatigue
  • Pale or yellowish complexion
  • Weakness
  • Shortness of breath
  • Irregular heartbeats
  • Dizziness or lightheadedness
  • Chest pain
  • Cold hands and feet
  • Headaches

Anaemia may start out being so mild that you don't notice it. However, as anaemia progresses, the symptoms get worse.2


Iron deficiency anaemia is the most common cause of anaemia and is more frequently seen in pregnant women or women with heavy periods. If you have any symptoms of anaemia, you should visit your doctor and discuss your treatment options. Iron supplements are commonly prescribed to restore the body's iron levels. However, iron supplements have been found to cause an increase in weight in some people. Therefore, people receiving iron therapy should get advice on the risks of weight gain and the advantages of a healthy diet; additionally, their serum ferritin and haemoglobin levels should be monitored to avoid administering iron for too long a period. 


  1. Iron deficiency anaemia. [Internet]. 2017 [cited 2022 Oct 2]. Available from:
  2. Anemia - Symptoms and causes. Mayo Clinic [Internet]. [cited 2022 Oct 2]. Available from:
  3. Ferrous fumarate: medicine to treat iron deficiency anaemia. [Internet]. 2022 [cited 2022 Oct 2]. Available from:
  4. What Are the Side Effects of Taking Iron Tablets? MedicineNet [Internet]. [cited 2022 Oct 2]. Available from:
  5. Yokus O, Gedik H. Is iron treatment related to weight gain in female patients with iron deficiency anemia? Egypt J Haematol [Internet]. 2016 [cited 2022 Oct 2]; 41(2):42. Available from:
  6. Iron Supplements for Anemia (Ferrous Sulfate): Types, Benefits & Side Effects. Cleveland Clinic [Internet]. [cited 2022 Oct 2]. Available from:
  7. Iron Side Effects. Fergon [Internet]. [cited 2022 Oct 2]. Available from:
  8. NHS. Taking Iron Supplements Information for patients [Internet]. 2018 Jun [cited 2022 Aug 11]. Available from:
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Hana Hailu

Master's degree, Brain Science, University of Glasgow

Hana Hailu is an accomplished academic with a strong foundation in the field of brain science and pharmacology. She is currently pursuing her Master's degree in Brain Science from the prestigious University of Glasgow (2021-2022). Prior to this, Hana earned her Bachelor of Applied Science (BASc) in Applied Pharmacology from Queen Margaret University, where she studied from September 2017 to September 2021. With her deep knowledge and dedication, Hana is poised to make significant contributions to the world of neuroscience and pharmacology.

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