[11][12] For prevention they are only recommended in those with poor absorption, heavy menstrual periods, pregnancy, hemodialysis, or a diet low in iron.

[14] Common side effects include constipation, abdominal pain, dark stools, and diarrhea.

[14] Iron pills have been used medically since at least 1681, with an easy-to-use formulation being created in 1832 using Chicken Liver extracts and majority from plants.

[23] Supplements by mouth should be taken on an empty stomach, optionally with a small amount of food to reduce discomfort.

[27] A 2014 Cochrane Review found that blood donors were less likely to be deferred for low hemoglobin levels if they were taking oral iron supplements, although 29% of those who took them experienced side effects in contrast to the 17% that took a placebo.

[28] Side effects of therapy with oral iron are most often diarrhea or constipation and epigastric abdominal discomfort.

[35] Because one of the functions of elevated ferritin (an acute phase reaction protein) in acute infections is thought to be to sequester iron from bacteria, it is generally thought that iron supplementation (which circumvents this mechanism) should be avoided in patients who have active bacterial infections.

Replacement of iron stores is seldom such an emergency situation that it cannot wait for any such acute infection to be treated.

Some studies have found that iron supplementation can lead to an increase in infectious disease morbidity in areas where bacterial infections are common.

For example, children receiving iron-enriched foods have demonstrated an increased rate in diarrhea overall and enteropathogen shedding.

A Cochrane systematic review published in 2016 found high quality evidence that iron supplementation does not increase the risk of clinical malaria in children.

[7] Individuals may be genetically predisposed to excessive iron absorption, as is the case with those with HFE hereditary hemochromatosis.

Generally, an interval of 2–3 hours between the iron intake and that of other drugs seems advisable, but is less convenient for patients and can impact on compliance.

This is the most common and well studied soluble iron salt sold under brand names such as Feratab, Fer-Iron, and Slow-FE.

A clinical study demonstrated that HIP increased serum iron levels 23 times greater than ferrous fumarate on a milligram-per-milligram basis.

Moderate-certainty evidence suggests response to treatment may be higher when IV ferric carboxymaltose, rather than IV iron sucrose preparation is used, despite very-low certainty evidence of increased adverse effects, including bleeding, in those receiving ferric carboxymaltose treatment.

[54] In many cases, use of intravenous iron such as ferric carboxymaltose has lower risks of adverse events than a blood transfusion and as long as the person is stable is a better alternative.

[56][57] A Cochrane review of controlled trials comparing intravenous (IV) iron therapy with oral iron supplements in people with chronic kidney disease, found low-certainty evidence that people receiving IV-iron treatment were 1.71 times as likely to reach their target hemoglobin levels.

It was unclear whether type of iron therapy administration affects the risk of death from any cause, including cardiovascular, nor whether it may alter the number of people who may require a blood transfusion or dialysis.

[58] Soluble iron salts have a significant risk of adverse effects and can cause toxicity due to damage to cellular macromolecules.

When used as a treatment for IBD-related anemia, very low certainty evidence suggests a marked benefit with oral ferric maltol compared with placebo.