Haematology
Oral iron
Iron supplements — First-line treatment for iron-deficiency anaemia — effective but often poorly tolerated.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Oral iron is the standard first treatment for iron-deficiency anaemia. It replaces the iron the body needs to make haemoglobin, the oxygen-carrying pigment in red blood cells.
How it works
The supplement provides iron for absorption in the gut, which the bone marrow then uses to build new, healthy red blood cells. The blood count begins to recover over a few weeks, but topping up the body's stores takes longer.
In practice
In practice two things improve results: confirming the deficiency is genuinely iron (checking ferritin and the blood picture rather than treating blindly) and managing the gut side-effects that drive people to stop. Nausea, constipation and dark stools are common; taking the dose with food, using a lower-strength salt, or even alternate-day dosing can all help, with growing evidence that less-frequent dosing may absorb as well and be better tolerated. We separate iron from interacting drugs and antacids, recheck the blood count to confirm response, and continue for a period after normalisation to refill stores.
Examples
Practical use
How to take it & use it well
- Take oral iron such as ferrous sulfate as prescribed to treat or prevent iron-deficiency anaemia; an empty stomach helps absorption, but taking it with a little food can reduce stomach upset if needed.
- A drink of orange juice or another source of vitamin C taken with your iron can help your body absorb it.
- Separate iron from tea, coffee, dairy, antacids and certain other medicines by a couple of hours, as these can reduce how much iron is absorbed.
- Expect your stools to turn dark or black while taking iron; this is harmless and expected.
- If side effects are troublesome, ask your clinician about taking it with food, trying a different salt, or less frequent dosing rather than stopping altogether.
- Keep iron well out of reach of children, as an overdose is dangerous for young children.
Common uses
- Iron-deficiency anaemia
- Prevention of deficiency in selected at-risk groups
Monitoring
- Haemoglobin and iron studies to confirm response
- Tolerability and adherence
- Continued treatment to replenish stores after levels normalise
Weighing it up
Advantages & disadvantages
Advantages
- It is an effective, low-cost way to correct iron-deficiency anaemia and restore energy levels.
- Tablets, capsules and liquids are available, so a form can usually be found to suit you.
- It can be taken at home without injections or infusions in most cases.
- Once stores are replenished, symptoms such as tiredness and breathlessness usually improve.
Disadvantages
- Stomach upset, nausea, constipation or diarrhoea are common and can affect how well people stick with it.
- It turns stools dark, which can be mistaken for bleeding or can mask it.
- It needs to be taken for weeks to months and absorption is easily reduced by food and other medicines.
- Accidental overdose is a serious danger to children.
Key safety principles
What to watch for
- Gastrointestinal upset (nausea, constipation, dark stools) is common and limits adherence.
- Reduces absorption of some drugs and is itself reduced by antacids — separate the doses.
- Iron is dangerous in overdose, particularly to children — store safely; investigate the cause of deficiency.
Key interactions
What to avoid or check alongside
- Antacids, calcium and some indigestion remedies reduce iron absorption, so they should be spaced apart.
- Iron lowers absorption of several antibiotics, including tetracyclines and quinolones, reducing their effect if taken together.
- Iron can reduce absorption of thyroid hormone (levothyroxine), so doses should be separated by several hours.
- Levodopa and some bisphosphonates for bones are also less well absorbed when taken close to iron.
- Tea, coffee and high-calcium foods taken at the same time can markedly reduce how much iron is absorbed.
Patient & carer advice
- Dark stools are harmless and expected
- If it upsets your stomach, taking it with food or less often can help — ask us
- Keep well away from children, and leave a gap from antacids and certain other medicines
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
Oral iron: frequently asked questions
Why have my stools turned black on iron tablets?
Dark or black stools are a normal, harmless effect of oral iron and are expected. However, if stools are tarry and you also feel unwell, or you see fresh red blood, contact your clinician, as iron can sometimes mask true bleeding.
What is the best time to take iron?
Iron is absorbed best on an empty stomach, ideally with a vitamin C source like orange juice and away from tea, coffee, dairy and antacids. If it upsets your stomach, taking it with a little food is a reasonable trade-off.
How long will I need to take iron for?
Iron is usually continued for several weeks to bring your blood count up, and often for a few months beyond that to refill your body's iron stores. Your clinician will check blood tests to decide when to stop.
What if iron tablets upset my stomach?
Stomach upset and constipation are common. Taking iron with food, trying a different iron salt, or taking it less often can help. Speak to your pharmacist or GP before stopping, as you may still need treatment for anaemia.
Can iron tablets be dangerous if a child swallows them?
Yes. Iron overdose is a serious and potentially fatal poisoning in young children. Always store iron in its original container, well out of reach, and seek emergency help immediately if a child swallows any.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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