Side Effects of Iron tablet / capsule / liquids

Iron deficiency is common in women’s health, often due to blood loss or issues related to the upper digestive tract. Iron deficiency can cause several symptoms like constant tiredness, trouble focusing, poor exercise performance, and a lower quality of life. 

Oral Iron formulations are commonly used to treat or prevent iron deficiency anemia. They help with iron deficiency but can cause side effects and has suboptimal efficacy due to limited absorption. Iron supplements come in different forms, such as tablets, capsules, drops, slow-release tablets, chewable tablets, and liquids.

The type of iron supplement chosen depends on how well it’s absorbed, its side effects, and how well the patient can handle it. Ferrous and ferric salts are the most common forms of iron in oral iron therapy.

Common Side Effects

Iron supplements are usually safe when taken at the recommended dose, but they can cause side effects like:

– Upset stomach

– Dark or black stools

– Bloating

– Constipation

– Diarrhoea

– Gas

– Nausea

– Stomach cramps

– Vomiting

– Metallic taste

– Teeth staining (mostly from liquids)

A study of 43 trials with 6,831 participants found that taking ferrous sulfate supplements led to more stomach and digestive problems compared to placebo or IV iron. The most common side effects were constipation, nausea, and diarrhoea. Side effects seemed to depend on the iron dose; one study found that higher doses of iron caused more stomach pain, nausea, vomiting, changes in bowel movements, and black stools¹.

Another study of over 10,000 patients found high rates of stomach and digestive problems with all oral iron types, including ferrous fumarate (43%), ferrous gluconate (31%), and ferrous sulphate (30%). These side effects may be caused by free radical production that leads to inflammation or changes to the gut’s natural bacteria. Iron-related gut issues were found in 16% of patients in one study¹.

It’s important to consider these side effects when giving oral iron, especially to pregnant people or those with inflammatory bowel disease. Other issues include liquid iron staining teeth, unpleasant metallic tastes, and some formulas not being properly digested¹.

1. Eur J Haematol. 2023; 110(2): 123–130.