An iron supplement
Ferrous fumarate
An oral iron supplement used to treat and prevent iron-deficiency anaemia.
What is Ferrous fumarate?
Ferrous fumarate is an iron supplement used to treat and prevent iron-deficiency anaemia, when the body lacks the iron needed to make healthy red blood cells. It is one of three common iron salts (with ferrous sulfate and ferrous gluconate) that work in the same way but contain different amounts of iron. It often causes harmless black stools, constipation and stomach upset, which taking it with food or on alternate days can ease. Keep it well away from children, because iron overdose can be very dangerous.
Education and reference only. This is a plain-language guide to Ferrous fumarate — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Ferrous fumarate is an oral iron salt used to treat and prevent iron-deficiency anaemia. Iron is needed to make haemoglobin, which carries oxygen in red blood cells, so a shortage causes tiredness, breathlessness and paleness. It is one of the common iron salts used in the UK and is taken as a tablet, capsule or liquid, usually over several months. It is sometimes combined with folic acid in pregnancy products.
How it works
Ferrous fumarate supplies iron the gut can absorb, which the body uses to rebuild haemoglobin and healthy red blood cells. As stores refill, anaemia symptoms such as tiredness usually improve over weeks. It differs from the other iron salts mainly in how much elemental iron it contains, but for most people it works and feels much the same.
Company & origin
Originated / developed by: Generic (long-established).
A widely used oral iron salt used in the UK to treat and prevent iron-deficiency anaemia.
Practical use
How to take Ferrous fumarate
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it with or just after food if it upsets your stomach, even though absorption is slightly better on an empty stomach.
- If side effects are a problem, your prescriber may advise taking it on alternate days, which can work just as well.
- Keep it a couple of hours apart from tea, coffee, milk, calcium supplements and antacids, which reduce iron absorption.
- Vitamin C, such as a glass of orange juice, can help your body take up the iron.
- Store all iron well out of the reach of children, as an overdose can be very dangerous.
Weighing it up
Advantages & disadvantages of Ferrous fumarate
Advantages
- An effective and inexpensive treatment for iron-deficiency anaemia.
- Comes as tablets, capsules and liquid, and works well on alternate-day schedules.
- Some products combine it with folic acid, which is convenient in pregnancy.
Disadvantages
- Frequently causes constipation, nausea and stomach upset.
- Darkens the stools, which can be confused with intestinal bleeding.
- Absorption is easily reduced by food, drinks and several medicines, so timing matters.
Practical use
Good to know
As with all oral iron, black or dark stools are normal and harmless, though black tarry stools with stomach pain should be checked. Constipation, nausea and stomach discomfort are common, and taking it with food or only on alternate days can make it easier to tolerate without losing much effect. Tea, coffee, milk and calcium supplements reduce absorption and are best separated, while vitamin C can help iron be absorbed. Iron must always be kept out of reach of children, as overdose can be very dangerous. Treatment is usually continued for a time after blood counts recover, to rebuild iron stores.
Who should not take it / use with caution
- People with iron-overload conditions such as haemochromatosis should not take iron unless advised.
- It is generally avoided in people who receive repeated blood transfusions unless a doctor recommends it.
- Used cautiously in active inflammatory bowel disease or known oral-iron intolerance.
Monitoring
- Blood tests to confirm haemoglobin and iron stores are improving.
- Reviewing tolerability and whether timing or alternate-day dosing helps.
- Looking for an underlying cause of iron deficiency if it persists or returns.
Side effects
- Constipation, nausea, stomach cramps and dark stools are common and usually harmless.
- Diarrhoea or heartburn in some people, often easing with food or alternate-day dosing.
- Rarely, severe stomach pain or black tarry stools that should be checked promptly.
Key interactions
- Reduces absorption of levothyroxine and some antibiotics such as tetracyclines and quinolones, so separate the doses.
- Calcium supplements, antacids and tea bind iron and lower how much is absorbed.
- Vitamin C can increase iron absorption; iron can affect certain bisphosphonate and Parkinson's medicines.
Available as: Tablets, capsules and oral liquid taken by mouth.
Answers
Ferrous fumarate: frequently asked questions
Is ferrous fumarate the same as ferrous sulfate?
They are different iron salts that work in much the same way; they mainly differ in how much elemental iron they contain, and a prescriber may switch between them for tolerability.
Why are my stools dark?
Iron normally darkens stools and this is harmless, but black tarry stools with stomach pain should be checked in case of bleeding.
Can taking it less often still work?
Yes. Taking iron on alternate days can be just as effective for many people and often causes fewer side effects.
Does it interact with my thyroid tablet?
Iron can reduce absorption of levothyroxine, so take them several hours apart as advised.
Why must I keep it from children?
Iron overdose can be very dangerous in children, so all supplements should be kept well out of their reach.
The wider class
About Iron supplements
Ferrous fumarate belongs to the iron supplements class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF
- NICE CKS
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.