Iron supplements: essential for some people, and a serious poisoning risk for young children

Iron supplements are a lifeline for many people with low iron, which can leave them tired, weak and struggling to concentrate, yet the same bottle on a kitchen counter can be dangerous to a curious toddler. An accidental overdose can be fatal for young children, which is why child-resistant caps and warnings matter so much. For adults, the everyday side effects are more ordinary: an upset stomach, nausea or constipation that can make a daily tablet hard to keep taking. People with an inherited condition that causes iron overload, and anyone on certain thyroid or Parkinson's medicines, should talk with a clinician first.

Everyday exposure: where you meet it and how much

Iron is a mineral the body needs to make hemoglobin, which carries oxygen in the blood. Most people get enough from food, including meat, seafood, beans, lentils, spinach and fortified flour and cereals. Supplements are common: ODS reports that 14% to 18% of Americans, and about 72% of pregnant women, use a supplement containing iron. Multivitamins for women typically provide 18 mg of iron, while many iron-only supplements provide 65 mg. [1]

The amount of iron in a supplement depends on its form. Ferrous sulfate is about 20% elemental iron by weight, ferrous fumarate about 33% and ferrous gluconate about 12%. Labels list the elemental iron, which is the figure that matters. The US tolerable upper intake level is 45 mg a day for adults and teens and 40 mg a day for younger children, although clinicians sometimes prescribe more to treat deficiency. [1]

Known and suspected harms

Evidence labels are editorial summaries, not individual risk predictions: established means recognized under the stated conditions; probable means a likely contribution with uncertainty; possible means limited evidence; disputed means assessors disagree. These labels do not describe how common an effect is.

• Established — accidental overdose can be fatal in young children: a single intake of more than 20 mg of iron per kg of body weight can cause corrosive injury to the intestine, shock and organ failure. Around 60 mg/kg can cause multisystem organ failure, coma and death. At least 43 US children died from swallowing high-dose iron supplements between 1983 and 2000. Child deaths fell after packaging and labelling changes. [1]
• Established — stomach upset, nausea and constipation at higher doses: doses of 45 mg a day or more may cause nausea and constipation, and other stomach effects are common with high doses. Taking iron with food can reduce these effects. [1]
• Established — iron overload in people with hereditary hemochromatosis: people with this genetic condition absorb too much iron. Without treatment, iron builds up and can damage the liver, heart and pancreas. Treatment includes avoiding iron and vitamin C supplements. [1]
• Established — reduced absorption of some thyroid and Parkinson's medicines: iron can reduce the absorption of levothyroxine, used for underactive thyroid, and levodopa, used for Parkinson's disease. Medicines that reduce stomach acid can also lower iron absorption. [1]

Reducing avoidable exposure and harm

Keep iron supplements, and multivitamins that contain iron, locked away or well out of children's sight and reach, in their child-resistant containers. If a child may have swallowed iron, call a poison centre or emergency services immediately, even if the child seems well. Take iron only as directed. Do not take more than the recommended dose without advice. Ask a pharmacist about spacing iron from thyroid or Parkinson's medicines and from calcium supplements. [1–3]

What it is

Supplements contain iron as salts or other compounds. The most common are ferrous (iron II) and ferric (iron III) salts such as ferrous sulfate, ferrous gluconate, ferric citrate and ferric sulfate. Ferrous sulfate's CAS number is 7720-78-7. Ferrous forms are more soluble and better absorbed than ferric forms. [1,5]

What it does and why it is used

Iron supplements prevent and treat iron deficiency and iron-deficiency anaemia, which can cause tiredness, weakness and difficulty concentrating. People at higher risk include pregnant women, infants and young children, women with heavy periods, frequent blood donors, and people with some gut conditions. Iron supplements can reduce the risk of iron-deficiency anaemia in pregnancy. [1]

Regulatory status and health context

Canada

Health Canada's multi-vitamin/mineral supplement monograph requires products with more than 250 mg of elemental iron per package to carry the statement "Keep out of reach of children. There is enough iron in this package to seriously harm a child", preceded by a prominent octagonal warning symbol. [3]

United States

FDA requires solid iron-containing supplements to carry this warning: "Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6. Keep this product out of reach of children. In case of accidental overdose, call a doctor or poison control center immediately." Since 1978, supplements with 250 mg or more of elemental iron per container must also be in child-resistant packaging. [1,2]

European Union

Directive 2002/46/EC on food supplements lists permitted iron sources, including ferrous sulfate. It requires maximum amounts to be based on upper safe levels. Labels must include a warning not to exceed the recommended daily dose and a statement that the product should be stored out of reach of young children. [4]

Environmental notes

The sources used here do not identify iron supplements as an environmental concern and do not provide data for a rating. [1,4]

Quick facts

• CAS (ferrous sulfate): 7720-78-7. [5]
• Purpose: prevent or treat iron deficiency. [1]
• Adult upper limit (US): 45 mg of iron a day, unless prescribed. [1]
• Danger dose for children: more than 20 mg/kg can cause serious injury. [1]
• Canada: packages with over 250 mg of iron must warn that they can seriously harm a child. [3]
• Key habit: store out of children's reach, even day to day. [1–4]

Sources

All URLs were fetched on 2026-11-10. Source publication dates differ from this draft's review date.

1. NIH Office of Dietary Supplements: Iron, fact sheet for health professionals.
2. eCFR: 21 CFR 101.17, food labeling warning statements.
3. Health Canada: Multi-vitamin/mineral supplements monograph.
4. EUR-Lex: Directive 2002/46/EC on food supplements.
5. PubChem PUG REST: ferrous sulfate synonyms.