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 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.
  • Oral iron therapy should be continued for 3 months after haemoglobin (Hb) optimised and then stopped. (Consider ongoing prophylactic dose 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.

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. An oral dose of 100 to 200mg elemental iron daily is needed to treat IDA. 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. Refer to BNF or summary of product characteristics (SPCs) for detailed information on 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.

Between 10-40% of patients will experience GI side effects and will not fully adhere to the prescribed course.  If adverse effects are troublesome, the following may help to minimise:

  • Taking with or after food (but doing so decreases absorption by 40-66%).
  • Reducing the dose frequency, or beginning therapy with a small dose and increasing gradually.
  • Trying an alternative salt/formulation with a lower content of elemental iron (refer to table 1 in full guideline).

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. An ongoing prophylactic dose (refer to BNF) should be considered in patients who are at a particular risk of IDA.

Failure to respond may be indicative of:

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

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 sulphate 200mg three times 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

45 year old male diagnosed with IDA and commenced on Galfer® (ferrous fumarate 305mg) twice 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 sulphate 200mg twice or three times daily (containing 65mg of elemental iron per dose).


Originally published 17/04/19 and updated on 07/12/2020. Links updated 08/03/22.

Links to updated guideline added 18/05/22. This blog is currently under review following the guideline update.

Medicines Update blogs are correct at the time of publication.