Iron-deficiency anaemia means the body does not have enough iron to make haemoglobin; the most common causes are heavy periods, pregnancy, a diet low in iron and hidden bleeding from the stomach or bowel [1, 2]. It is diagnosed with a full blood count (CBC) and a ferritin test, and in adults a ferritin of 30 or less is a sign of iron deficiency [3]. Treatment is usually one iron tablet a day or every other day, on an empty stomach, until about 3 months after the haemoglobin is back to normal; and in men and post-menopausal women the cause must be found with an endoscopy and a colonoscopy [1, 2].
Key points
- Iron deficiency is one of the most common causes of anaemia worldwide [26]. It usually gets better with iron tablets, but finding its cause matters just as much [1].
- Common causes: heavy periods, pregnancy and breastfeeding, a diet low in iron, blood donation, and slow, hidden bleeding from the stomach or bowel [1, 2].
- Ferritin shows your iron stores: in adults, a ferritin of 30 or less is a sign of iron deficiency, and below 15 means the iron stores are almost empty [3, 1].
- Take iron tablets once a day or every other day, in the morning on an empty stomach with water or orange juice, not with tea, coffee or milk [1, 2, 6, 11]. Dark stools are normal [1].
- Haemoglobin usually starts to rise within 2 to 4 weeks; keep taking the tablets for about 3 months after it is back to normal, to refill your iron stores [1].
- In men and in women after the menopause, unexplained iron-deficiency anaemia should be followed up with a check of the stomach and bowel, because it is sometimes the only sign of a disease of the gut [1].
What is iron-deficiency anaemia?
Iron is needed to make haemoglobin, the protein in red blood cells that carries oxygen around the body. Most of the body’s iron is in haemoglobin, so losing blood is the most important cause of losing iron [2].
Iron deficiency develops slowly: first the iron stores (measured with a ferritin test) run down while the haemoglobin is still normal; this is called “iron deficiency without anaemia”. If the shortage continues, the haemoglobin falls and iron-deficiency anaemia develops [1].
The World Health Organization defines anaemia in adults as a haemoglobin below 13 in men and below 12 in non-pregnant women (grams per decilitre) [2]. Worldwide, about 4 in 10 young children and more than 1 in 3 pregnant women have anaemia [26].
Iron-deficiency anaemia is not cancer and usually has a simple cause; but in men and post-menopausal women it is sometimes the first sign of hidden bleeding from a disease of the bowel or stomach [1]. Read more: Can anaemia be a sign of cancer?
Common causes of iron deficiency
Heavy periods
Pregnancy and breastfeeding
A diet low in iron
Hidden bleeding from the gut
Stomach ulcers, long-term use of anti-inflammatory painkillers and aspirin, polyps and bowel or stomach cancer can bleed slowly and silently [1]. This bleeding usually cannot be seen and shows itself only as iron-deficiency anaemia [28].
Poor absorption of iron
Coeliac disease (a reaction of the gut to gluten), Helicobacter infection, long-term inflammation of the stomach, stomach surgery and long-term use of acid-reducing medicines such as omeprazole all reduce how much iron is absorbed [1].
Symptoms of iron-deficiency anaemia
Common symptoms of iron deficiency and iron-deficiency anaemia [2, 26]:
- tiredness, lack of energy and less stamina for work and exercise
- dizziness or light-headedness, headache and ringing in the ears
- shortness of breath, especially on exertion, and palpitations
- paleness, cold hands and feet and feeling cold
- restless legs at rest or in bed (restless legs syndrome)
- hair loss, dry skin and hair, brittle or spoon-shaped nails and a smooth tongue
- craving ice, soil or other non-food items; this may be a sign of severe iron deficiency
In children, iron deficiency can affect motor development and learning, and in older people it is often linked with declining memory and thinking [2]. These symptoms have other causes too, so iron deficiency should be confirmed with a blood test before any treatment [1].
If your anaemia comes with unexplained fever, repeated infections, unexplained bruising or bleeding, swollen lymph nodes or an enlarged liver and spleen, your doctor will also consider blood cancers, and you should have a blood count within 2 days [27]. Read: What are the symptoms of leukaemia? and Blood cancers.
Which tests? What does a low ferritin mean?
The two main tests are a full blood count (CBC) and ferritin [1, 2]. On the CBC, a low haemoglobin shows anaemia, and small (low MCV) and pale (low MCH) red cells point to iron deficiency [1]. Small red cells can also be due to thalassaemia trait; if you have been told you are a carrier, for example in a premarital test, tell your doctor [1]. Read: What is thalassaemia minor? and How to read a CBC.
Ferritin shows how much iron the body has in store and is the single most useful test for iron deficiency [1]. Ferritin rises with inflammation, infection and chronic disease, so it may be reported as “normal” even when iron is low. In that case your doctor also looks at the transferrin saturation (TSAT) [1, 3].
| Ferritin (nanograms per millilitre) | What it means |
|---|---|
| Below 15 | Iron stores are almost empty; this almost always means iron deficiency [1, 4] |
| 30 or less | Iron deficiency; the American Society of Hematology proposed this threshold in 2026 for adults, including women who have periods and pregnant women [3] |
| 30 to 45 | Iron deficiency is still possible, especially with inflammatory diseases [1, 5] |
| Below 100 with an inflammatory disease or chronic infection | Iron deficiency is possible; your doctor also measures the transferrin saturation, and a value below 20% points to iron deficiency [3] |
| Above 150 | Iron deficiency is unlikely, even with inflammation [1] |
Ferritin is reported in nanograms per millilitre or micrograms per litre, which give the same number. The lower limit on your lab report may differ from this table; go through the result with your doctor.
Do I need my stomach and bowel checked?
Finding the cause of iron deficiency is part of the treatment [1]:
- Men of any age and women after the menopause: a stomach endoscopy and a colonoscopy are usually the first tests, because in them iron deficiency is often due to slow bleeding from the gut [1, 5].
- All adults: a urine test and a blood test for coeliac disease [1].
- Women before the menopause: the cause is usually periods, pregnancy and diet, and gut disease is uncommon; a check of the stomach and bowel is needed if you are 50 or over, do not have periods, have warning signs in the gut, have a strong family history of bowel cancer, or your anaemia keeps coming back despite treatment [1].
- Aged 60 or over: in the UK national guideline, any anaemia, even without iron deficiency, leads to a stool test for hidden blood to guide referral [27].
Do not delay iron tablets because of these tests; only if a colonoscopy is due within the next two weeks may your doctor wait until after it to start them [1]. Read more: Can anaemia be a sign of cancer? and Blood in your stool: piles or bowel cancer?
For physicians
Diagnostic thresholds. WHO 2020: ferritin below 15 µg/L in people aged 5 years and over and below 12 under 5 in apparently healthy individuals; with infection or inflammation, below 70 in adults and below 30 in children (conditional recommendation, low certainty) [4]. ASH 2026: 30 ng/mL or less in non-pregnant, non-menstruating adults, in menstruating people and in pregnancy (with a strong recommendation against the 15 threshold in pregnancy); 20 or less from 9 months to 4 years; in anaemia of inflammation, ferritin together with TSAT, with iron deficiency if ferritin is below 100 ng/mL or TSAT below 20%; in situations such as symptoms, abnormal bleeding, upcoming surgery, planned pregnancy or pregnancy with anaemia, a threshold of 50 or less; all recommendations conditional with low or very low certainty except that strong recommendation [3]. EHA 2024: below 30 µg/L in adults, adolescents and children over 5 and below 12 under 5; in inflammation below 100 together with TSAT; at least 45 over 65 years with CKD or CHF [2]. BSG 2021: ferritin below 15 has a specificity of 0.99, a cut-off of 45 a specificity of 0.92, and above 150 absolute iron deficiency is unlikely even with inflammation; an Hb rise of 10 g/L or more within 2 weeks strongly suggests absolute iron deficiency [1]. AGA 2020: cut-off 45 ng/mL (sensitivity 85%, specificity 92%) [5].
Investigation of the cause. BSG 2021: confirm iron deficiency before investigation; urinalysis and coeliac serology (3–5% of IDA) for all; in men and post-menopausal women with new IDA, gastroscopy and colonoscopy first line, with CT colonography if colonoscopy is unsuitable; young men follow the same algorithm; premenopausal women, after coeliac serology, only with age over 50, no menstruation, warning symptoms, high genetic risk (two first-degree relatives with CRC or one under 50) or IDA that is recurrent or out of proportion to menstrual loss; after a good-quality negative BDE with an inadequate response or recurrence, capsule endoscopy and renal tract investigation; after Hb normalisation, CBC every 3 months for 12 months and then every 6 months for 2–3 years [1]. AGA 2020: BDE in asymptomatic men and post-menopausal women (strong recommendation), BDE suggested over iron replacement alone in premenopausal women (conditional), non-invasive Helicobacter testing after a negative BDE, coeliac serology with small-bowel biopsy only if positive [5]. NICE NG12: FIT to guide referral in any adult with IDA and in people aged 60 and over with anaemia even without iron deficiency [27]. EHA: heavy menstrual bleeding (more than 80 mL per period) is the most common cause; in HMB with recurrent or refractory IDA and no uterine lesion, screen for inherited bleeding disorders such as von Willebrand disease (present in 20–30% of women with HMB) [2].
Treatment: how should I take iron tablets?
How to take iron tablets correctly
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One tablet a day, or every other day
One tablet a day is usually enough, and splitting it into several doses a day does not increase absorption [1, 8]. Taking it every other day is also a good option: in studies, iron was absorbed better and caused fewer gut side effects [8, 10]. Your doctor will choose one depending on how severe the anaemia is.
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In the morning on an empty stomach, with water or orange juice
Iron tablets are absorbed best on an empty stomach; taking them with food can cut absorption by up to three quarters [1]. In one study, taking the tablet with coffee or with breakfast and coffee cut iron absorption to less than half, and taking it with orange juice delivered about 4 times more iron than taking it with coffee or breakfast [11]. Keep tea, coffee, milk and dairy products at least an hour apart from the tablet [1, 2].
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Do I need vitamin C?
Guidelines disagree on this. The American Gastroenterological Association suggests adding vitamin C for better absorption [6], but British and European guidelines do not consider it necessary, because in a large study iron tablets alone and iron tablets with vitamin C raised haemoglobin by the same amount [1, 2, 14]. If you wish, take the tablet with orange juice; in one study it increased iron absorption [11].
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Common side effects and what to do
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How long?
Haemoglobin usually rises within the first 2 weeks, and your doctor repeats the blood test within the first 4 weeks [1]. It may take 6 to 12 weeks to return fully to normal [2]. Once it is normal, keep taking the tablets for about 3 more months to refill your iron stores [1, 2]. After that, your doctor repeats the blood count every few months so that any return of iron deficiency is found early [1].
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Keep a gap between iron and other medicines
Iron reduces the absorption of some medicines: take the thyroid medicine levothyroxine at least 4 hours apart from iron [21], and tetracycline antibiotics such as doxycycline at least 2 hours apart [20]. Acid-reducing medicines such as omeprazole and antacids also reduce iron absorption [1]; if you take these medicines, tell your doctor.
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Keep out of reach of children
Accidental overdose of iron products is a leading cause of fatal poisoning in children under 6. Keep tablets out of children’s reach, and if a child swallows iron tablets, call your local emergency number or poison centre at once [20].
When is intravenous iron needed?
Most people get better with tablets, and in most of them intravenous iron does not raise the haemoglobin much faster [1]. Intravenous iron is used when [1, 2, 6]:
- iron tablets are not tolerated, even every other day
- tablets have not worked; for example, the haemoglobin has not risen after 2 to 4 weeks
- the gut does not absorb iron well, as in active inflammatory bowel disease or after weight-loss surgery
- bleeding is continuing or iron needs to be replaced quickly, for example before surgery or in the second and third trimesters of pregnancy
- you also have chronic kidney disease or heart failure
Intravenous iron is not given in the first trimester of pregnancy [2]. It is given in a hospital or clinic, and many types take 15 to 40 minutes [1]; the staff watch you for an allergic reaction for at least 30 minutes afterwards [17, 19]. Severe reactions are very rare [6]. One type (ferric carboxymaltose) can lower the phosphate level in the blood; if you develop tiredness, weakness or pain in your muscles, bones or joints after the infusion, tell your doctor [17]. A blood transfusion is needed only for very severe anaemia with serious symptoms [1].
For physicians
Hepcidin and oral dosing. In iron-depleted women (ferritin ≤20 µg/L), doses of 60 mg or more raised hepcidin for 24 hours and reduced fractional absorption of the next dose by 35–45%; a sixfold increase in dose (40–240 mg) only tripled the iron absorbed (6.7–18.1 mg); doses of 40–80 mg and avoiding twice-daily dosing maximise fractional absorption [7]. In the Stoffel 2017 trial, 60 mg on alternate days (28 days) versus consecutive days (14 days): cumulative fractional absorption 21.8% versus 16.3% (P=0.0013) and total absorption 175.3 versus 131.0 mg (P=0.0010); splitting 120 mg into two doses did not increase absorption and raised hepcidin more [8]. In women with IDA (100 and 200 mg ferrous sulfate), fractional absorption on days 2 and 5 was 40–50% higher than on day 3, and 200 mg on alternate days delivered about twice the iron of 100 mg on consecutive days [9].
Clinical outcomes. Double-blind trial (150 women, ferritin ≤30 µg/L; 100 mg daily for 90 days versus alternate days for 180 days): at equal total doses, ferritin 43.8 versus 44.8 µg/L (P=0.98), more gastrointestinal side effects on intake days with daily dosing (LPR 1.56), and iron deficiency at 6 months 11.4% versus 3.0% (P=0.049) [10]. Meta-analysis of 11 trials (1014 participants): a slightly greater but non-significant Hb rise with daily dosing (MD 0.28 g/dL; 95% CI −0.01 to 0.56), similar adverse events (RR 1.07) except more metallic taste with daily dosing; very low certainty of evidence for most outcomes [12]. In a small double-blind trial (60 women with ferritin <20 µg/L, 14 days), 60 mg daily raised MCV and MCH more than 120 mg on alternate days [13]. BSG: 60 mg twice daily raised Hb faster than 120 mg on alternate days, but after the same total dose the Hb rise was similar, with less nausea on alternate days [1].
Guideline recommendations. BSG: one tablet a day (50–100 mg elemental iron, for example one 200 mg ferrous sulfate tablet containing 65 mg) taken fasting; if not tolerated, alternate days, another preparation or intravenous iron; modified-release preparations and added vitamin C are not recommended; monitor Hb within the first 4 weeks: no rise of 10 g/L after 2 weeks predicts failure (sensitivity 90.1%, specificity 79.3%); with alternate-day dosing, review at 28 days (a rise of 20 g/L or into the normal range); continue for about 3 months after Hb normalises [1]. EHA: 60–80 mg and alternate-day regimens; Hb normalises in 6–12 weeks and treatment continues for at least 3 months after that (target ferritin >100 µg/L); children 3–6 mg/kg/day and adolescents 65–130 mg once daily [2]. AGA 2024: at most once a day; alternate-day dosing may be better tolerated by some patients; add vitamin C [6]. In the vitamin C trial (440 patients, 100 mg iron every 8 hours with or without 200 mg vitamin C), the change in Hb at 2 weeks was 2.00 versus 1.84 g/dL (difference 0.16; 95% CI −0.03 to 0.35; equivalent) [14]. In an absorption study, coffee reduced fractional absorption by 54% and breakfast with coffee by 66%, and 80 mg ascorbic acid increased it by 30% [11]. Ferrous sulfate versus placebo: OR for gastrointestinal side effects 2.32, and versus intravenous iron 3.05, with no relation to dose [15].
| Drug | Dose | Administration | Safety note |
|---|---|---|---|
| Iron sucrose (Venofer) | 200 mg per dose, 5 doses over 14 days (total 1000 mg) in non-dialysis CKD [19] | Slow IV injection over 2–5 minutes or infusion in up to 100 mL saline over 15 minutes [19] | FDA indication only IDA in CKD; BSG: maximum 200 mg per dose [19, 1] |
| Ferric carboxymaltose (Injectafer, Ferinject) | 50 kg or more: 750 mg in two doses at least 7 days apart (total 1500 mg), or 15 mg/kg up to 1000 mg as a single dose; under 50 kg: 15 mg/kg in two doses at least 7 days apart [17] | Slow IV push at about 100 mg per minute, or infusion of up to 1000 mg in no more than 250 mL saline (concentration at least 2 mg/mL) over at least 15 minutes [17] | Boxed warning for symptomatic hypophosphataemia; check phosphate before a repeat course in people at risk or a repeat course within 3 months [17] |
| Ferric derisomaltose (Monoferric, Monofer) | 50 kg or more: 1000 mg as a single dose; under 50 kg: 20 mg/kg as a single dose [18] | IV infusion over at least 20 minutes [18] | Less hypophosphataemia than ferric carboxymaltose in two trials: 7.9% versus 75.0% and 8.1% versus 73.7% [16] |
All products only where treatment for anaphylaxis is immediately available, with monitoring for at least 30 minutes after the infusion [17, 19].
Indications. BSG: when oral iron is contraindicated, ineffective or not tolerated; from the outset in ongoing significant bleeding, GI malabsorption, iron deficiency combined with anaemia of inflammation, problems with administration (such as severe dysphagia) or adherence; the Hb response to intravenous and oral iron is usually similar [1]. EHA: intolerance (even of alternate-day dosing), inadequate response (Hb <10 g/dL by week 4), need for rapid replacement (including less than 6 weeks before surgery), IBD, CKD, CHF, malabsorption, after bariatric surgery, ongoing abnormal uterine bleeding, IDA in the second or third trimester and IRIDA; not to be used in the first trimester [2]. AGA 2024: formulations that replace the deficit in 1 or 2 infusions are preferred; all formulations carry similar risks, true anaphylaxis is very rare, and most reactions are complement activation-related pseudo-allergy and should be treated as such [6].
Safety and total dose. Serious anaphylactic reactions occurred in 0.1% (2 of 1775) in ferric carboxymaltose trials; in pregnancy, a hypersensitivity reaction may be accompanied by fetal bradycardia [17]. EHA: no test dose except for iron dextran, and no premedication except in asthma or a history of drug allergy; Ganzoni formula: weight (kg) × (target Hb minus patient’s Hb, g/dL) × 2.4 plus iron stores (500 mg above 35 kg, with a target Hb of 15 g/dL); the formula is no longer used for ferric carboxymaltose and ferric derisomaltose; reassess 3 months after the last dose [2]. Blood transfusion only for severe symptomatic anaemia or circulatory compromise, with a target Hb of 70–90 g/L (80–100 in unstable coronary disease), followed by iron replacement [1].
Iron-rich foods
There are two kinds of iron in food:
- Iron from animal foods such as red meat, chicken, fish and eggs, which is absorbed better [2, 24].
- Iron from plant foods such as lentils, beans and other pulses, dark green leafy vegetables, tofu and iron-fortified cereals, which is absorbed less well [24, 25].
Eating iron-rich plant foods with fruit and vegetables rich in vitamin C, such as citrus fruits, tomatoes, cabbage and broccoli, increases iron absorption [24, 25]. On the other hand, tea, coffee, calcium and phytate reduce iron absorption; it is best to drink tea at least an hour after a meal [1, 25].
A good diet helps stop your iron stores running down again, but when you have iron-deficiency anaemia, guidelines recommend treatment with iron medicine [2]. Vegetarians absorb less iron from food and are among the groups who should be checked for iron deficiency from time to time [25, 2].
Pregnancy, heavy periods and children
Pregnancy. The need for iron rises in pregnancy. Iron-deficiency anaemia in pregnancy increases the risk of premature birth and low birth weight, and makes bleeding after the birth more dangerous if it happens [2]. The World Health Organization recommends a daily iron tablet with folic acid for all pregnant women; folic acid is best started before pregnancy [22]. If iron-deficiency anaemia is found in pregnancy, only iron tablets are given in the first trimester, and from the second trimester intravenous iron if needed [2]. If you are a thalassaemia carrier, tell your doctor: Thalassaemia minor and pregnancy.
Heavy periods. If you need to change your pad or tampon more often than every 2 hours, need to change it at night as well, your period lasts more than 7 days, or you pass clots the size of a coin or larger, see a doctor [23]. Treating the bleeding itself matters as much as the iron tablets, otherwise the iron stores do not refill; and if iron deficiency keeps coming back despite treatment, your doctor may check for inherited bleeding disorders such as von Willebrand disease [2, 23].
Children. Growing children, especially babies born early and teenagers, are more likely to become iron deficient [2]. The doctor works out the dose of iron drops or syrup from the child’s weight; give it on an empty stomach and apart from milk and dairy products. Iron drops can stain the teeth; afterwards rinse the mouth and brush the teeth [2]. Keep iron tablets and drops out of children’s reach [20].
When should I see a doctor urgently?
Call your local emergency number or go to an emergency department straight away if:
- you vomit blood or your stools are black and tarry, especially with dizziness or weakness; these are signs of bleeding in the gut [28]. Iron tablets also darken the stools; if you are not sure, ask straight away [1].
- you feel very dizzy when you stand up, are breathing very fast or have a very fast heartbeat, or feel faint [26]
- a child has swallowed iron tablets [20]
See a doctor in the next few days if:
- you are a man or a post-menopausal woman with iron-deficiency anaemia; the cause needs to be found [1]
- your anaemia comes with a change in bowel habit, blood in your stools, unexplained weight loss or abdominal pain [27]
- your periods are heavy, for example you change your pad or tampon more often than every 2 hours [23]
- after 4 weeks of iron tablets you feel no better or your haemoglobin has not risen [1]
- you are pregnant and have symptoms of anaemia [2]
Frequently asked questions
Does a low ferritin without anaemia need treatment?
A low ferritin with a normal haemoglobin is called iron deficiency without anaemia. If you have symptoms such as tiredness, treatment with iron tablets is reasonable; in women before the menopause, iron has reduced tiredness [1, 2]. Your doctor will also look for the cause and repeat the blood count from time to time [1].
Should I take iron tablets in the morning or at night?
Why is my anaemia not getting better despite iron tablets?
Common reasons: not taking the tablets regularly, poor absorption in the gut, continuing bleeding, chronic illness, or another cause of anaemia as well, such as a lack of vitamin B12 or folic acid [1]. In this case your doctor will consider further tests or intravenous iron [1]. Read: Vitamin B12 deficiency
Is intravenous iron better than tablets?
Is iron-deficiency anaemia dangerous, or a sign of cancer?
It usually has a simple cause and gets better with treatment [1]. But in men and post-menopausal women it is sometimes the only sign of hidden bleeding from the bowel or stomach, including from cancer, and needs to be investigated [1]. Read: Can anaemia be a sign of cancer?
Should I take iron tablets in pregnancy?
High ferritin with anaemia: what does it mean?
A ferritin above 150 makes iron deficiency unlikely, even when there is inflammation [1]. A high ferritin should not be judged on its own, and your doctor will find its cause with an examination and other tests [4]. Read: High LDH, ferritin or ESR: do they mean cancer?
Related links
References
28 referencesShow all referencesClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults
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- 7Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women
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- 9Iron absorption from supplements is greater with alternate day than with consecutive day dosing in iron-deficient anemic women
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- 12Efficacy of daily versus alternate day oral iron supplementation for management of anaemia among general population: a systematic review and meta-analysis
- 13Daily oral iron supplementation produced greater improvements in hematological parameters than alternate day doses - A pilot double-blind randomized control trial in iron-deficient young women
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- 16Effects of Iron Isomaltoside vs Ferric Carboxymaltose on Hypophosphatemia in Iron-Deficiency Anemia: Two Randomized Clinical Trials
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- 21SYNTHROID (levothyroxine sodium) tablets: Prescribing Information
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