Iron is an essential mineral used to make haemoglobin, the protein in red blood cells that carries oxygen. Iron supplements treat and prevent iron deficiency and iron-deficiency anaemia — the commonest nutritional deficiency in the world. Low iron is a finding, not a diagnosis.
What is Iron?
Iron supplements are sold as tablets, capsules and syrups, mostly as general-sale or pharmacy products. The South African Medicine Price Registry lists some, such as Ferrimed syrup (iron polymaltose complex, 50 mg elemental iron per 5 ml, Schedule 1).
(A search of that register for “iron” also returns spironolactone products, because the letters appear inside the word. Those are a diuretic and entirely unrelated. Disregard them if you search it yourself.)
What iron does in the body is mostly one job done very well. About two-thirds of the body’s iron sits in haemoglobin, binding oxygen in the lungs and releasing it in the tissues. The rest is in myoglobin in muscle, in enzymes involved in energy production, and in stores in the liver and bone marrow.
Without enough iron, the marrow makes red cells that are smaller and paler than normal, carrying less oxygen. That is iron-deficiency anaemia, and the tiredness it causes is a genuine oxygen-delivery problem rather than a vague one.
The forms differ, and the numbers on the box are confusing.
| Form | Note |
|---|---|
| Ferrous sulphate | Cheapest, most common; 200 mg tablet provides ~65 mg elemental iron |
| Ferrous fumarate, ferrous gluconate | Similar; different salt weights |
| Iron polymaltose complex | Better tolerated; absorbed differently |
| Sucrosomial iron | Newer, better tolerated, more expensive |
Compare the “elemental iron” figure, not the salt weight. A 200 mg ferrous sulphate tablet is not 200 mg of iron — it is about 65 mg. This is the single most common source of confusion when comparing products.
What is Iron commonly used for?
- Iron-deficiency anaemia — the main use.
- Iron deficiency without anaemia, where stores are low but haemoglobin has not yet fallen. This causes fatigue, poor concentration, reduced exercise tolerance and hair shedding, and is frequently missed because the full blood count looks normal — ferritin is the test that shows it.
- Heavy menstrual bleeding, one of the commonest causes in women.
- Pregnancy, where requirements rise substantially.
- Growth in infancy and adolescence.
- Vegetarian and vegan diets, where iron is present but absorbed less efficiently.
- After surgery or blood loss.
- Malabsorption — coeliac disease, inflammatory bowel disease, after bariatric surgery, and long-term acid-suppressing medicines.
- Chronic kidney disease and blood donors.
The most important point on this page: iron deficiency is a finding, not a diagnosis. Iron is lost through bleeding, and in adults — particularly men, and women past menopause — unexplained iron deficiency can be the first sign of bleeding in the gut that needs investigating, sometimes from something serious.
If you have not had the reason for your deficiency explained, ask. That single question matters more than which brand you take.
Do not take iron without a confirmed need. Iron overload is genuinely harmful, the body has no way to excrete excess, and roughly 1 in 200 people of European ancestry carries a haemochromatosis gene variant.
Who commonly looks for Iron and why
- Women with heavy periods, who lose iron month after month.
- Pregnant women, where supplementation is routine.
- People told their haemoglobin or ferritin is low.
- People with persistent fatigue, hoping iron is the answer — for whom a blood test is the useful step.
- Vegetarians and vegans.
- Parents of toddlers, where iron deficiency is common.
- People who could not tolerate iron tablets because of constipation or nausea.
- Athletes, particularly endurance runners and menstruating athletes.
What to check on the label before taking Iron
- The elemental iron content, not the salt weight. This is the number that matters.
- The form, if tolerance has been a problem — polymaltose and sucrosomial iron are generally gentler than ferrous sulphate.
- Whether other supplements already contain iron. Multivitamins and pregnancy supplements often do.
- Whether it contains vitamin C, which improves absorption of conventional iron salts.
- The dosing frequency. Current evidence increasingly supports once daily, or even alternate-day dosing, which absorbs better than multiple daily doses — because a large dose raises hepcidin, a hormone that then blocks absorption for the next day or so.
- Expiry date and storage.
Taking it well:
- Take it on an empty stomach if you can tolerate it, with vitamin C or orange juice.
- Avoid tea, coffee, dairy and calcium within about two hours — all substantially reduce absorption. Tea in particular is a strong inhibitor.
- Expect black stools. This is normal and harmless.
- Continue for three to six months after levels normalise, to rebuild stores. Stopping when haemoglobin recovers is the commonest reason deficiency returns.
Safety, interactions and when to seek professional advice
Common effects are constipation, nausea, stomach cramps, black stools and a metallic taste. Constipation is the usual reason people stop — taking it with food, using a gentler form, or moving to alternate-day dosing usually solves it.
Iron is a leading cause of serious accidental poisoning in young children. A handful of adult iron tablets can be fatal to a toddler, and the tablets often look like sweets. Store iron out of sight and reach, and get emergency help immediately if a child swallows any — take the pack with you, and do not wait for symptoms.
Speak to a doctor or pharmacist before taking iron if you:
- Have not had iron deficiency confirmed by a blood test.
- Have haemochromatosis or another iron-overload condition, or a family history of one.
- Have had repeated blood transfusions, or have thalassaemia or sickle cell disease.
- Have inflammatory bowel disease or a stomach ulcer.
- Take thyroid medicine (levothyroxine), tetracycline or quinolone antibiotics, bisphosphonates, levodopa, or HIV medicines such as dolutegravir — iron blocks absorption of all of these. Separate them by at least two hours.
- Take antacids or proton pump inhibitors, which reduce iron absorption.
- Are pregnant, where dosing should be guided by your clinician.
Stop and seek advice for severe abdominal pain, vomiting, or black stools accompanied by pain — note that iron normally darkens stools, and that alone is not a concern.
See a doctor rather than self-treating for symptoms of anaemia — persistent tiredness, breathlessness on mild exertion, pallor, dizziness, brittle nails, hair loss, restless legs, or unusual cravings for ice or non-food substances (pica). And ask for a repeat blood test a few months in: treatment that is not working needs a reason found, and treatment that has worked still needs stores rebuilt.
Related supplement guides
Frequently asked questions
What is iron used for in the body? Mainly making haemoglobin, which carries oxygen in red blood cells. It is also in muscle myoglobin and in enzymes involved in energy production.
What are iron supplements used for? Treating and preventing iron deficiency and iron-deficiency anaemia — from heavy periods, pregnancy, growth, poor absorption, blood loss or a restricted diet.
Do I need a blood test first? Yes. Iron deficiency should be confirmed, and — importantly — the reason for it established. In adults it can be the first sign of bleeding that needs investigating.
Why does it constipate me? Unabsorbed iron in the gut is irritating. Taking it with food, using a gentler form such as polymaltose or sucrosomial iron, or alternate-day dosing usually helps.
Should I take it every day? Current evidence increasingly supports once-daily or even alternate-day dosing, which absorbs better than multiple daily doses.
Can I take it with tea or milk? Not at the same time. Tea, coffee, dairy and calcium substantially reduce absorption — separate them by about two hours.
Why are my stools black? Normal and harmless with iron. Black stools with pain are different and need attention.
How long do I take it for? Usually three to six months after levels normalise, to rebuild stores. Stopping too early is why deficiency often returns.