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Iron supplements: what to be careful with
Iron supplements restore iron stores when they are depleted, most often after a blood test has shown low ferritin or iron-deficiency anaemia.
General information only, and not exhaustive. This is not medical advice, not a full list of interactions, and not a reason to start, stop or change a medicine. Interactions depend on the exact drug, the dose, your other medicines and your own health — a pharmacist or doctor is the one who decides. Always read the leaflet that came with your medicine, and ask your pharmacist before adding anything, including supplements.
Group, not a brandATC B03A
Examples in this group: ferrous sulfate, ferrous fumarate, ferrous gluconate, iron bisglycinate. Interactions usually belong to the whole group, but your own leaflet is brand-specific — always the final word.
Food and drink to be careful with
- Tea, coffee and cocoa. Polyphenols in tea and coffee bind iron in the gut and can cut absorption substantially. A cup with the tablet is one of the commonest reasons a supplement underperforms; a gap of an hour or two is the usual advice.
- Calcium and dairy. Calcium competes with iron for absorption. Milk with the tablet, or a calcium supplement at the same moment, reduces the amount that gets in.
- Vitamin C helps. Ascorbic acid in the same meal improves absorption of non-haem iron. Orange juice with the tablet is the standard everyday version of that advice.
- Phytates and fibre. Wholegrains and legumes contain phytate, which binds iron. This is not a reason to avoid them — they are good foods — but it is why the tablet is often taken away from the main meal.
Timing around meals
Iron is absorbed best on an empty stomach, but that is also when it causes the most nausea and constipation. Taking it with a little food is the usual compromise, at the cost of some absorption. How much to take and for how long is set by whoever ordered the blood test.
Alcohol
No routine interaction. In haemochromatosis and in liver disease the relationship between alcohol and iron is a clinical matter and iron supplements are not used casually.
Other things to watch
- Iron reduces the absorption of levothyroxine, tetracycline and quinolone antibiotics, and bisphosphonates — separation in time is the standard answer.
- Black stools are expected on iron and are not bleeding; genuine blood is a different colour and a different matter.
- Iron overdose is dangerous, particularly in children, which is why these are kept out of reach.
If anything here does not match what you were told, or you notice a new symptom after starting a medicine, contact your pharmacist or doctor — do not just stop taking it. Stopping some medicines suddenly is more dangerous than any food interaction.
Source: The product's own Summary of Product Characteristics and patient information leaflet, published per medicine by the licensing authority. The tea, calcium and vitamin C effects on non-haem iron absorption are standing points in iron product information and in dietary guidance. · checked 2026-09-02
Frequently asked questions
What should I avoid with iron supplements?
Tea, coffee and cocoa is the one people ask about most: Polyphenols in tea and coffee bind iron in the gut and can cut absorption substantially. A cup with the tablet is one of the commonest reasons a supplement underperforms; a gap of an hour or two is the usual advice. This is general information — your leaflet and pharmacist have the specifics.
Can I drink alcohol with iron supplements?
No routine interaction. In haemochromatosis and in liver disease the relationship between alcohol and iron is a clinical matter and iron supplements are not used casually.
Should iron supplements be taken with food?
Iron is absorbed best on an empty stomach, but that is also when it causes the most nausea and constipation. Taking it with a little food is the usual compromise, at the cost of some absorption. How much to take and for how long is set by whoever ordered the blood test.
Other medicine groups
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Metformin
Metformin lowers blood glucose mainly by reducing the amount of glucose the liver releases, and is usually the first medicine used in type 2 diabetes.
Levothyroxine
Levothyroxine replaces the thyroid hormone the body is not making enough of, in an underactive thyroid.
Warfarin
Warfarin thins the blood by blocking the vitamin K-dependent clotting factors, and is used to prevent and treat blood clots.
DOACs (direct oral anticoagulants)
DOACs thin the blood by directly blocking a single clotting factor, and are used to prevent stroke in atrial fibrillation and to treat and prevent venous clots.
SSRIs and SNRIs
These antidepressants raise the availability of serotonin (and for SNRIs also noradrenaline) in the brain, and are used for depression and several anxiety conditions.
All medicine groups · Alcohol units and clearance · Blood test reference ranges
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