Supplement
Iron for women
Iron is a mineral whose authorised health claims in Great Britain include roles in normal red blood cell and haemoglobin formation, oxygen transport and reducing tiredness and fatigue. The NHS says heavy periods and pregnancy are very common causes of low iron, but tiredness has many causes, so low iron is best confirmed with a GP blood test before you take a supplement. The NHS also says the common iron tablets work much the same at the same dose of iron, and that a side effect from one type may not happen with another. Your GP or pharmacist sets the dose.
What it does
Iron is an essential mineral. In Great Britain, the health claims a product may make are listed in the Great Britain nutrition and health claims register (updated 19 May 2026, checked 1 November 2026). The authorised claims for iron include:
- The claim that iron contributes to normal formation of red blood cells and haemoglobin.
- The claim that iron contributes to normal oxygen transport in the body.
- The claim that iron contributes to the reduction of tiredness and fatigue.
- The claim that iron contributes to the normal function of the immune system.
Check with a GP before taking iron. The NHS says 17 mg or less a day from supplements is unlikely to cause harm, and low iron is confirmed with a GP blood test.
How much iron you need
These are the NHS daily amounts for women. The NHS says "You should be able to get all the iron you need from your daily diet."
| Who | How much iron a day |
|---|---|
| Women aged 19 to 49 | 14.8mg |
| Women aged 50 and over | 8.7mg |
- The NHS adds: "Women having periods after the age of 50 may need the same amount of iron as women aged 19 to 49."
- On supplements, the NHS says: "Taking 17mg or less a day of iron supplements is unlikely to cause any harm. But continue taking a higher dose if advised to by a GP."
- Too much can cause side effects. The NHS says: "Side effects of taking high doses (over 20mg) of iron include: constipation, feeling sick, being sick, stomach pain."
- The NHS also says: "Very high doses of iron can be fatal, particularly if taken by children, so always keep iron supplements out of the reach of children."
Talk to a GP before taking more than 17mg a day. To see how much iron is in everyday foods, download our iron-rich foods list (PDF), or open the printable version.
Iron supplements: check with a blood test first
Tiredness has many causes, and low iron is only one of them. The NHS iron deficiency anaemia page lists tiredness and lack of energy, shortness of breath, noticeable heartbeats, paler than usual skin and headaches as symptoms, and says to see a GP if you think you might have it. The GP "will usually do a blood test", called a full blood count. The same page says "Heavy periods and pregnancy are very common causes of iron deficiency anaemia", and that the GP recommends treatment once the reason has been found.
On iron tablets, the NHS ferrous sulfate page says: "If you feel tired, but have not been diagnosed with iron deficiency anaemia, it's important to talk to your doctor or pharmacist before taking ferrous sulfate. This is because there may be other reasons why you lack energy."
Talk to a GP or pharmacist before you take iron if any of these apply. The NHS ferrous fumarate page says you may not be able to take it if you have:
- anaemia that is not caused by low iron levels
- sickle cell disease or thalassaemia
- a stomach ulcer or stomach problems such as IBS (irritable bowel syndrome)
- regular blood transfusions
- been told that you have too much iron in your body
The same NHS page says you can usually take it if you are pregnant, "but check with a doctor first", and lists medicines that may affect it, including antibiotics such as doxycycline or ciprofloxacin, antacids, other supplements with magnesium, calcium or zinc, and levothyroxine for the thyroid. If you are in perimenopause and your periods have changed, note it on our menopause symptoms checklist and take it to the appointment.
The main types of iron tablet
Most iron tablets are an iron salt. The BNF, published by NICE, says "Ferrous salts show only marginal differences between one another in efficiency of absorption of iron" and that the choice "is thus usually decided by the incidence of side-effects and cost". The NHS puts it like this: "There is little difference in how well they work when you take the same dose of iron. If you have a side effect with one type of iron, it may not happen with another type."
| Type | What UK guidance says |
|---|---|
| Ferrous sulfate (or sulphate) | The NHS calls it "a type of iron that's used as a medicine to treat and prevent iron deficiency anaemia". It comes as tablets or drops, on prescription or from a pharmacy. |
| Ferrous fumarate | The NHS calls it "a medicine that treats low iron levels". It comes as tablets, capsules or liquid, on prescription or from a pharmacy. |
| Ferrous gluconate | The NHS names it as another type of iron, and the BNF lists it with the other iron salts. |
| Iron bisglycinate | Sold as a food supplement. It is not one of the iron salts in the BNF summary, and we did not find an NHS or NICE page that describes it, so we cannot say how it compares. |
Side effects of iron tablets
The NHS says some people get side effects from iron tablets:
- constipation or diarrhoea
- tummy pain
- heartburn
- feeling sick
- darker than usual poo
The NHS suggests taking the tablets "with or soon after food to reduce the chance of side effects", and says "It's important to keep taking the tablets, even if you get side effects." The NHS ferrous sulfate page says to leave a 2 hour gap before having tea or coffee, dairy products or eggs, "because they can stop your body absorbing iron". Darker poo is common on iron, but the NHS says to talk to a doctor or call 111 straight away "if your poo is black, tar-like or red, or has blood in or on it, or if you also feel unwell in any other way". If a side effect bothers you, speak to a pharmacist or GP: the NHS says that with a different type of iron, the same side effect may not happen.
Who sets the dose
We do not give treatment doses on this page, because the right dose depends on your blood results and why you are low. The NHS says your dose "depends on why you're taking it", that you should follow a doctor's instructions if it is prescribed, and follow the instructions on the packet if you buy it from a pharmacy.
Treatment takes time. The NHS says you'll need to take iron tablets "for about 6 months", and your GP may do repeat blood tests to check your iron level is getting back to normal. The BNF says people should be checked in the first 4 weeks for a response. If you bought iron without a prescription, the NHS says: "Do not take ferrous fumarate for longer than 6 months if you bought it without a prescription. See a GP if your symptoms get worse or do not get better."
Who it is for
Women can be more likely to have low iron because of menstruation, and needs rise in pregnancy. That does not mean everyone should supplement; it means iron is worth checking with a blood test if you have symptoms. A varied diet including red meat, pulses, leafy greens and fortified foods supplies iron for most people. It is for adults; in pregnancy, address it with your midwife.
What to look for when buying
- Do not self-diagnose. Tiredness has many causes, and a blood test is how low iron is confirmed.
- Check the amount of iron per serving on the label. The NHS does not name one type of iron as the gentlest.
- Vitamin C can support iron absorption, while tea, coffee and calcium taken at the same time can reduce it; some products pair iron with vitamin C.
- If you are pregnant, the NHS advises addressing iron with your midwife rather than self-prescribing.
Named UK brands to compare
The products below cover different formats. Where our own product appears, it's labelled and sold directly by us. Links to other sellers may earn us a commission, which does not affect how we grade the evidence.
Thinking about iron before pregnancy? See our trying to conceive guide for preconception nutrition.
Check it yourself
Check any product against the upper safe limit checker and the recommended daily intake lookup before you buy. Supplemental iron above the reference figure should be a decision you make with your GP, not off a label. Before reaching for a supplement, see how much iron is in everyday foods with our printable iron-rich foods list.
Frequently asked questions
What does iron do?
It helps make red blood cells and haemoglobin, carry oxygen, reduce tiredness and fatigue, and support immune function. What it does, above, lists the authorised wording.
Should I take iron if I feel tired?
Not without checking first. Tiredness has many causes, so see your GP if you are persistently tired; the blood test section above explains why.
Which form of iron is gentlest on the stomach?
The NHS does not name one type as the gentlest. It says that if you have a side effect with one type of iron, it may not happen with another type, and that taking iron with or soon after food can reduce side effects. For ferrous fumarate it adds that if side effects happen, "you may need to take it on alternate days instead". Your GP or pharmacist can help you choose.
Do I need iron in pregnancy?
Iron needs rise in pregnancy, but the NHS advises addressing iron with your midwife based on your blood tests rather than self-prescribing a high dose. See our pregnancy guide for context, and always check with your midwife or GP first.
This is information, not medical advice, and is not a substitute for a registered clinician. Speak to your GP or pharmacist before starting a supplement.
Editor, Her Vitals
Oliver leads Her Vitals's editorial coverage of women's life-stage health and supplements. He curates and reviews existing branded products across trying to conceive, pregnancy, postnatal, perimenopause, menopause and the senior years, weighing what the evidence supports against guidance from bodies such as EFSA, the NHS and NICE, and is clear that the content is information rather than medical advice.
AI-assisted check: