Iron

Is taking iron safe?

For someone who is iron-deficient, yes, and it can transform how they feel. For someone who is not, iron supplements bring side effects with no benefit and some real risks. Iron is unusual among supplements: the body has no active way to get rid of excess, so what you absorb stays until you bleed or shed cells.

That is why iron scores lower than most vitamins and minerals in this section. It is effective medicine for the right person and an unnecessary risk for the wrong one.

Doses and limits

Measure	Amount of elemental iron
Adult man, daily need (US RDA)	8 mg
Woman 19 to 50, daily need	18 mg
Pregnancy, daily need	27 mg
US upper limit, age 14 and over	45 mg
EFSA safe level, adults (2024)	40 mg
Ferrous sulphate 200 mg tablet	about 65 mg

The US upper limit was set to avoid stomach side effects, not organ damage. Treatment doses for deficiency often exceed it, which is fine under medical supervision. EFSA reviewed iron in 2024 and found the data too thin to set a formal upper limit, so it set a "safe level" of 40 mg a day instead.

Always check the elemental iron figure. A 325 mg ferrous sulphate tablet in the US contains about 65 mg of iron; a 200 mg tablet in the UK contains about the same.

Overdose in children

Before 1997, iron was the leading cause of fatal poisoning in US children under 6. Brightly coated tablets look like sweets, and a few adult-strength tablets can be enough to poison a toddler. Iron overdose corrodes the gut, then damages the liver; a child may seem to recover after vomiting before becoming critically ill a day or two later.

In 1997 the FDA required a warning on every iron product and unit-dose blister packs for products with 30 mg or more. Only one child death from iron was reported in the US between 1998 and 2002. A court struck down the packaging rule in 2003, but the warning label remains. Keep iron, including prenatal vitamins, locked away.

Iron overload and haemochromatosis

Hereditary haemochromatosis is a genetic condition in which the gut absorbs too much iron. It is among the most common genetic disorders in people of Northern European descent: roughly 1 in 200 to 300 carry two copies of the main gene variant (C282Y), though not all of them develop overload. Excess iron builds up in the liver, heart, pancreas and joints over decades, causing cirrhosis, heart failure and diabetes. Many people do not know they have it, and taking iron supplements speeds the damage. People with thalassaemia and some other anaemias also risk overload.

This is a strong reason not to take iron without a blood test.

Interactions

Iron reduces the absorption of several medicines, and some medicines reduce iron absorption:

• Levothyroxine: separate by at least 4 hours.
• Quinolone and tetracycline antibiotics, bisphosphonates, levodopa: separate by at least 2 hours; check the exact gap with a pharmacist.
• Antacids and PPIs such as omeprazole reduce iron absorption.
• Calcium and tea taken at the same meal reduce absorption.

Iron does not interact with warfarin in a clinically important way, but combined iron and magnesium products need spacing from the same list of drugs.

Who should talk to a doctor first

• Anyone thinking of taking iron without a diagnosed deficiency.
• Men and postmenopausal women, who rarely need it unless they are losing blood. Unexplained deficiency in these groups needs investigation.
• People with haemochromatosis, thalassaemia, liver disease or frequent blood transfusions.
• People with inflammatory bowel disease, in whom oral iron can worsen symptoms.
• Pregnant women, beyond what is in a prenatal vitamin.

How we scored it

Quality (86) is strong because iron salts are simple to make accurately. Dose safety (70), interactions (72) and regulatory actions (72) are mid-range, and organ toxicity (62) is the weakest factor because of fatal childhood overdoses and iron overload. The score sits below vitamin D, which has a wider margin between useful and harmful doses.