Greater Glasgow and Clyde Medicines

Treatment of IDA – Oral Iron Therapy

An updated GGC guideline on the Treatment of Iron Deficiency Anaemia (IDA) is now available here. An abbreviated version of this guideline is also available in the GGC Adult Therapeutics Handbook here.

Key messages:

  • Patients diagnosed with clinically significant IDA should have iron replacement therapy to correct anaemia and replenish iron stores.

  • Treatment should normally be conducted in parallel with investigations to determine the underlying cause. However, for some patients such as those with complex multi-morbidity or approaching end of life, such investigations may not be appropriate.

  • Oral iron is the first line treatment of choice*.

  • Prescribe ferrous fumarate 210mg or ferrous sulfate 200mg once a day as initial therapy (see below for information on dosing)

  • Oral iron therapy should be continued for 3 months after haemoglobin (Hb) optimised and then stopped. (Consider ongoing prophylaxis in at risk patients).

  • The irritant adverse effects of oral iron are related to the amount of elemental iron taken rather than the type of preparation.

  • Iron preparations with a low content of elemental iron must be tried (with food) before acceptance of genuine intolerance to oral iron.

* In patients with heart failure with reduced ejection fraction, New York Heart Association (NYHA) class III with an left ventricular ejection fraction (LVEF) of ≤ 45%, or NYHA class II with an LVEF ≤ 40%, who have a Hb level of 95 to 135 g/L) and iron deficiency (defined as ferritin < 100 micrograms/L or ferritin < 300 micrograms/L if TSAT < 20%), oral iron therapy is not effective in iron repletion, and does not improve exercise capacity. IV iron should be used in preference to oral iron in this patient group.


Oral iron replacement therapy
Treatment with iron replacement therapy should be considered for patients with clinically relevant IDA in whom the clinical benefit of treatment outweighs any risks. Treatment of an underlying cause should prevent further iron loss, but all patients should have iron supplementation both to correct anaemia and replenish body stores. Traditionally oral iron salts were taken as a split dose, two or three times a day (100-200mg elemental iron daily). More recent data suggests a once daily dose of 50-100mg of elemental iron (e.g. ferrous fumarate 210mg OD), taken in the fasted state, may be just as effective while probably associated with lower rates of adverse effects. Refer to table 1 in full guideline for elemental iron content of different preparations.


Iron supplements are not well absorbed orally (particularly for patients with inflammation). They are best absorbed on an empty stomach as the presence of food may further impair absorption. The absorption may be reduced if taken concurrently with other drugs. In addition, iron supplements may decrease the absorption of some drugs. Examples include tetracycline and fluoroquinolone antibiotics, where the concomitant oral administration of oral iron may result in loss of antibiotic absorption and treatment failure (See blog on Antibiotic Treatment Failure Risk for more details on these interactions. Refer to BNF or summary of product characteristics (SPCs) for detailed information on additional drug interactions.

Adverse gastrointestinal effects

Oral iron preparations can cause gastrointestinal (GI) irritation and abdominal pain with nausea, vomiting, diarrhoea and constipation. Failure to swallow the tablets properly can lead to marked local ulceration in the mouth or oesophagus. The irritant adverse effects are related to the amount of elemental iron taken rather than the type of preparation.

With traditional three times daily dosing, between 10-40% of patients would experience GI side effects and not fully adhere to the prescribed course. The reduced initial dose of once daily should help minimise these adverse effects, however, if adverse effects are troublesome, the following may help to minimise:

  • Taking with or after food (but doing so can reduce bioavailability by up to 75%).
  • Reducing the dose frequency to alternate days if taking once daily, or to once daily if currently prescribed two or three times daily.
  • Trying an alternative salt/formulation with a lower content of elemental iron (refer to table 1 in full guideline for more details).

Monitoring response

Response to oral iron can be confirmed by monitoring the rise in Hb. Where patients take treatment effectively, Hb should rise by 20g/L over 4 weeks. Treatment should be continued for 3 months after Hb is optimised and then stopped. Ongoing prophylaxis (refer to BNF) should be considered in patients who are at a particular risk of IDA such as those who have:

  • Recurring anaemia (such as in an elderly person) and further investigations are not indicated or appropriate.
  • An iron-poor diet (e.g. vegans).
  • Malabsorption (e.g. coeliac disease).
  • Menorrhagia.
  • Had a gastrectomy.

Failure to respond may be indicative of:

  • Non-compliance - assess and improve adherence.
  • Continued blood loss - investigate and treat underlying cause.
  • Malabsorption.
  • Wrong diagnosis - recheck ferritin and reassess.

Other reasons for poor response include active infection, renal or hepatic disease or malignancy.


Treatment with oral iron: case scenarios

(Refer to diagnostic and treatment algorithm in full guideline for further information and GGC laboratory reference ranges).

Scenario one

65 year old female diagnosed with IDA and commenced on ferrous sulfate 200mg once daily. Baseline blood results Hb 90g/L, ferritin 13micrograms/L. Bloods rechecked 4 weeks later Hb 92g/L, ferritin 30micrograms/L.

  • Poor response to oral iron (Hb levels should rise by at least 20g/L over 4 weeks).

  • Ferritin level is higher, therefore anaemia likely to have been due to combination of both IDA and blood loss.

  • Refer for further investigation of ongoing blood loss.


Scenario two

84 year old attends for a polypharmacy review following a recent fall. He has a diagnosis of IDA in his past medical history and is on ferrous fumarate 210mg three times a day. His lastest Hb is 105g/L. He complains of constipation and admits to non-compliance with his iron therapy.

  • Discuss restarting his iron therapy at the reduced dose of once a day which is less likely to be associated with constipation and GI upset.

  • Advise to take iron on an empty stomach to increase absorption.

  • If GI side effects remain an issue, consider reducing the dose further to one tablet on alternate days.

  • Recheck Hb 4 weeks after re-starting iron.


Scenario three
45 year old male with IDA and on Galfer® (ferrous fumarate 305mg) once daily. Baseline blood results Hb 100g/L, ferritin 12microgams/L. Bloods rechecked 4 weeks later Hb and ferritin levels unchanged.

  • Poor response to oral iron (Hb levels should rise by at least 20g/L over 4 weeks).
  • Consider non-compliance as reason for non response.
  • Patient is on an iron preparation which contains 100mg of elemental iron per dose. These preparations can cause significant GI side effects and use should be discouraged. In this case consider giving a different iron formulation or salt with lower content of elemental iron e.g. ferrous sulfate 200mg once daily (containing 65mg of elemental iron per dose).


A series of blog articles relating to this guideline are available:

Updated Guideline - Treatment of IDA
Diagnosis of IDA - Iron Studies
Treatment of IDA - IV iron therapy

Originally published 17/04/19 and updated on 05/12/22.
Medicines Update blogs are correct at the time of publication.