Iron supplements
Iron supplements are supplements that can be prescribed by a doctor for a medical reason. Iron can also be a dietary supplement, which can be purchased in supermarkets etc. These 2 categories should not be confused.

# Indications
Iron supplements are used in medicine to treat iron-deficiency anemia.
First, it must be clear that iron deficiency and not another factor (e.g. chronic, low-grade, undetected blood loss such as fecal occult blood) causes the anemia. Preventive measures must be discussed with the patient (for example when the patient is on a strict vegetarian diet because inorganic iron in plants has a lower bioavailability, or elderly patients with a poor diet).
Another indication for giving extra iron is the second and third trimester of pregnancy, generally in association with folic acid. Indeed, in some condition like growth, menstruation and pregnancy, the body's need for iron is increased. Supplements may be needed to reach RDA goals.

# Administration
Iron can be supplemented using various pharmacological forms, such as iron(II) sulphate (this is the most common and cheapest salt, e.g. Feratab , Fer-Iron  , Slow-FE ,...) , and in complex with gluconate, dextran, carbonyl iron, and other salts. Sometimes ascorbic acid is added for better absorption.
Generally, iron supplementation therapy is an oral therapy, and parenteral iron therapy  (intravenously or intramuscular) is only given when resorption is seriously compromised (by illnesses, or when the patient cannot swallow) and benefit from oral therapy cannot be expected. Its more expensive and has increased morbidity.
Since iron stores in the body are generally depleted, and there is a limit to what the body can process (about 100mg per day) without iron poisoning, this is a chronic therapy which may take 3-6 months. In some conditions (e.g. after gastrectomy), in which there is production of intrinsic factor by the parietal cells of the stomach is complicated), even permanent iron substitution is necessary.
Patients at risk of acute complications may be candidates for transfusion. Patients with anemia of chronic disease may benefit from erythropoietin.

# Side effects
Side effects of therapy with iron are most often diarrhea or constipation and epigastric abdominal discomfort. Taken after a meal, side effects decrease but there is an increased risk of interaction with other substances. Side effects are dose-dependent, and the dose may be adjusted.
The patient may notice that his/her stools become black. This is completely innocent, but patients must be warned about this to avoid unnecessary concern. When iron supplements are given in a liquid form, teeth may reversibly discolor (this can be avoided through the use of a straw). Intramuscular injection can be painful, and brown discoloration may be noticed.
When haematopoiesis resumes, other essentials for this process (such as folic acid or  vitamin B12) may be depleted, and care must be taken to avoid deficiencies of these elements.

# Contraindications
Documented hypersensitivity and anemias without proper work-up (i.e. documentation of iron deficiency). Hypersensitivity reactions can be very dramatic if iron is administered intravenously.

# Interactions
Iron forms an insoluble complex with several other drugs, resulting in decreased absorption of both iron and the other drug. Examples include tetracycline, penicillamine, methyldopa, levodopa, bisphosphonates and quinolones. The same can occur with elements in food, such as calcium. Absorption of iron is better at a low pH (an acid environment), and resorption is decreased if there is a simultaneous intake of antacids, phosphates, etc.
Taken after a meal, there are less side effects but there is also less absorption because of interaction and pH alteration. Generally, an interval of 2-3h between the iron intake and that of other drugs seems advisable.

# Precautions
Children who ingest tablets may become intoxicated, in which case they should be taken to an emergency department. Some formulations (like carbonyl-iron) may be safer.

# Follow-up
Follow-up is needed to ensure compliance and to detect adequate response to therapy. If not, this may indicate another cause of anemia. Haematocrit, reticulocyte percentage, MCV, MCH and MCHC (the latter three being signs of microcytic anemia) should increase.