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Moderate evidenceVitamins & minerals

Ferrous Fumarate

A standard iron salt with about 33% elemental iron. It treats iron-deficiency anemia as well as ferrous sulfate; in the one head-to-head trial it also caused the most side effects.

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What the science says

  • As effective as other iron salts Moderate evidence

    A randomized trial in 120 pregnant women with iron-deficiency anemia compared ferrous sulfate, fumarate, ascorbate and carbonyl iron at 200 mg elemental iron/day. All four were equally effective on haemoglobin and iron indices and equally cost-effective; adverse effects were most frequent in the fumarate group (56.7%).

  • Absorption matches ferrous sulfate Moderate evidence

    A stable-isotope study in Mexican women, infants and young children found no significant difference in iron absorption between ferrous fumarate and ferrous sulfate, with relative bioavailability of 86–106% depending on the group.

Dosage & safety

Studied dose200 mg ferrous fumarate provides about 65 mg elemental iron. Trial evidence favours a single morning dose, or alternate-day dosing, over splitting the dose through the day. Take with vitamin C and away from tea, coffee, dairy and calcium.
SafetyConstipation, dark stools, nausea and abdominal pain are frequent and dose-related. Iron overdose is a leading cause of poisoning death in young children — keep it sealed and out of reach. Do not supplement without a documented deficiency; people with haemochromatosis must avoid it. Separate from levothyroxine, tetracyclines and quinolones by several hours.

How to take it

TimingA single morning dose, or alternate days, rather than split through the day.
With food?Best on an empty stomach, but take it with a little food if nausea would otherwise stop you continuing.
Worth knowingTake it with orange juice and keep tea, coffee, dairy and calcium at least two hours away — and keep the bottle sealed and out of children's reach, since iron overdose kills small children.

Interactions

With medications

  • levothyroxine

    Iron binds it in the gut and reduces absorption substantially. separate by at least 4 hours

  • tetracycline and quinolone antibiotics

    Mutual chelation reduces absorption of both. separate by at least 2–4 hours

  • proton-pump inhibitors and antacids

    Less stomach acid means less iron absorbed. take iron with vitamin C and as far from the antacid dose as possible

  • levodopa and methyldopa

    Iron chelates them and lowers their effect. separate by at least 2 hours

With other supplements

  • calcium

    Calcium competes with iron for absorption. take them at different times of day

  • vitamin C

    Vitamin C substantially increases non-heme iron absorption. take them together deliberately

  • zinc

    High doses compete for the same absorption pathways. separate by at least 2 hours

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Is ferrous fumarate as effective as ferrous sulfate?

Yes: a randomized trial in 120 pregnant women found ferrous fumarate as effective as ferrous sulfate and two other iron forms for anaemia, and an isotope study found similar absorption. The same trial found ferrous fumarate caused the most side effects (56.7%).

How much iron is in 200 mg ferrous fumarate?

200 mg of ferrous fumarate provides about 65 mg of elemental iron, as ferrous fumarate is about 33% elemental iron.

When is the best time to take ferrous fumarate?

Trial evidence favours a single morning dose of ferrous fumarate, or alternate-day dosing, over splitting it through the day. Take it on an empty stomach with vitamin C or orange juice, and keep tea, coffee, dairy and calcium at least two hours away.

What are the side effects of ferrous fumarate?

Constipation, dark stools, nausea and abdominal pain are frequent and dose-related with ferrous fumarate; a little food helps if nausea would stop you. Iron overdose is a leading cause of poisoning death in young children, so keep it sealed and out of reach.

Scientific references

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