Metformin
medicationA cheap, decades-old diabetes pill that some people ask about for weight and healthy aging.
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No. 067supplement
Iron
Iron is a supplement that is sold over the counter.
Also known as Iron supplements, Ferrous sulfate, Ferrous gluconate, Iron bisglycinate
Iron carries oxygen in red blood cells. Low iron causes fatigue, weakness and anemia, and is common in pregnancy, with heavy periods, in frequent blood donors and with some gut conditions. A ferritin blood test shows how much iron the body has stored.
Is Iron FDA-approved?
Sold without a prescription. Supplements are not reviewed by the FDA before sale, so third-party testing matters. Sold as a dietary supplement. Federal rules require iron supplements to carry a warning that accidental overdose is a leading cause of fatal poisoning in children under 6.
As of October 7, 2026.
Key takeaways
- Iron supplements treat iron deficiency, which is common in pregnancy, with heavy periods, in frequent blood donors and with some gut conditions.
- A ferritin blood test shows the body's iron stores and is the usual first step before taking iron.
- Constipation, nausea and stomach upset are common side effects.
- Accidental iron overdose is a leading cause of fatal poisoning in children under 6, so storage matters.
How does Iron work?
Iron is part of hemoglobin, which carries oxygen in red blood cells. When stores run low, the body first draws on ferritin reserves; if they run out, red cells become small and pale (iron deficiency anemia), causing fatigue and breathlessness.
The body absorbs only part of the iron it is given, and a hormone called hepcidin rises after iron is taken and reduces absorption for a time. A 2017 study in iron-depleted women found that giving iron on alternate days led to better total absorption than consecutive days.
What does a ferritin test tell you about iron?
MedlinePlus says ferritin is a protein that stores iron, and low ferritin suggests iron deficiency. Inflammation, liver disease, cancer and obesity can raise ferritin even without iron overload. MedlinePlus: Ferritin blood test
NIH notes serum ferritin measures iron stores but can be affected by inflammation, so clinicians often read it alongside other tests. NIH ODS: Iron fact sheet for health professionals
What does the evidence say about Iron?
Strong human evidenceIron supplements reliably treat iron deficiency. The USPSTF found insufficient evidence to recommend routine iron in pregnancy without deficiency.
What do clinicians say about Iron?
Clinicians recommend iron when testing shows deficiency, and look for the cause, rather than suggesting it to everyone who feels tired.
NIH lists pregnant women, infants and young children, women with heavy menstrual bleeding, frequent blood donors and people with cancer, GI disorders or heart failure as groups at risk of deficiency.
NIH ODS: Iron fact sheet for health professionalsIn 2024 the USPSTF found insufficient evidence to weigh the benefits and harms of routine screening or routine iron supplementation in pregnant people without symptoms.
USPSTF: Screening and supplementation for iron deficiency and iron deficiency anemia during pregnancy (JAMA 2024)Federal labeling rules require iron supplements to warn that accidental overdose is a leading cause of fatal poisoning in children under 6.
21 CFR 101.17(e): Required warning on iron-containing supplements (Cornell LII)NIH says people with hereditary hemochromatosis should avoid iron and vitamin C supplements.
NIH ODS: Iron fact sheet for consumers
Summaries of published guidelines, drug labels, regulators and reviews, each attributed to its source. DiscoverMedica does not employ clinicians.
Is Iron right for you, and who should avoid it?
Often considered for
- People with iron deficiency or iron deficiency anemia confirmed by a blood test
- People at high risk, such as those with heavy periods or frequent blood donation, after talking with a clinician
Not a fit, or needs extra care
- People with hemochromatosis or other iron overload
- Anyone who has not had their low iron confirmed and its cause looked for
- People taking levothyroxine or levodopa need to separate them from iron
Only a licensed clinician who knows your history can decide whether it is right for you.
What are the risks and side effects of Iron?
- Constipation, nausea, stomach pain and diarrhea are common, especially on an empty stomach.
- Keep it locked away from children: accidental iron overdose can kill a young child.
- People with hemochromatosis should avoid iron supplements.
- Iron reduces absorption of levothyroxine and levodopa; calcium and acid reflux drugs reduce iron absorption.
What should you ask a clinician about Iron?
- Should I check ferritin and a blood count before taking iron?
- What could be causing low iron in my case?
- How should I time it around my thyroid medicine or calcium?
These save with the compound when you add it to My Journal, so they’re on the printout for your visit.
How do people buy Iron?
No prescription is needed. Supplement brands and retailers sell it online and in stores.
Check with a clinician or pharmacist first if you take prescription medication or have a chronic condition.
Choose a product with independent testing, such as NSF Certified for Sport or USP Verified, because FDA does not check supplements before they are sold.
Labs you may be asked for
- Ferritin
- Complete blood count (hemoglobin)
- Iron and total iron-binding capacity in some cases
Check your levels first
Some services let you order common lab tests yourself, so the results are ready for your visit. Your clinician decides which labs, if any, you need, and what the results mean.
- Function HealthAnnual membership for broad lab panels, drawn at Quest sites or at home.Visit
- Quest HealthOrder individual lab tests from Quest Diagnostics online, without a doctor’s visit.Visit
From each service’s own site, checked September 23, 2026.
Where some people buy it
- ThorneSells iron bisglycinate direct to consumers.
- iHerbCarries iron supplements from many brands.
- Quest HealthNot a seller of supplements. Sells an iron, TIBC and ferritin panel you can order without a doctor visit.
From each provider’s own site, checked October 7, 2026. Programs change, so confirm the details before you sign up.
Where can I get Iron?
16 providers list Iron on DiscoverMedica, lowest listed price first.
$9.50listed price†
Buy at Pure Encapsulations $10.59listed price†
Buy at Nature Made $19.99listed price†
Buy at Momentous $21.00listed price†
Buy at Life Extension † Prices as listed by the provider when we checked; they change.
Iron: questions, answered
What are the side effects of iron supplements?
NIH says iron supplements, especially on an empty stomach, can cause upset stomach, constipation, nausea, abdominal pain, vomiting and diarrhea. Iron can reduce absorption of levothyroxine and levodopa. Most importantly, keep iron out of reach of children, because accidental overdose can be fatal in young children.
What does low ferritin mean?
Ferritin is a protein that stores iron, so MedlinePlus explains that a low level suggests iron deficiency, even before anemia appears. A normal or high ferritin does not always rule deficiency out, because inflammation, liver disease and obesity can raise it. Your clinician interprets ferritin together with a blood count and your symptoms.
Should I take iron every day or every other day?
Ask your clinician. A 2017 study in iron-depleted women found alternate-day iron led to better total absorption than consecutive days, because a hormone called hepcidin rises after iron and blocks the next absorption. The authors said this needs confirming in people with anemia, so the right schedule is an individual decision.
Should women take iron supplements?
Only when there is a reason. NIH lists heavy menstrual bleeding and pregnancy among the main risk factors for deficiency, so many women benefit from a ferritin test. In pregnancy, the USPSTF found insufficient evidence for routine iron supplementation without deficiency, so decisions should be made with an obstetric clinician.
Do iron supplements need a prescription?
No. Oral iron is sold over the counter as a dietary supplement, mostly as ferrous or ferric salts. Federal rules require a warning about fatal poisoning in children. Because iron deficiency has causes worth finding, such as blood loss, and because iron overload is harmful, testing before you start is the safer route.
Important safety information
Key risks
- Constipation, nausea, stomach pain and diarrhea are common, especially on an empty stomach.
- Keep it locked away from children: accidental iron overdose can kill a young child.
- People with hemochromatosis should avoid iron supplements.
- Iron reduces absorption of levothyroxine and levodopa; calcium and acid reflux drugs reduce iron absorption.
Talk to a clinician first, or avoid it, if
- People with hemochromatosis or other iron overload
- Anyone who has not had their low iron confirmed and its cause looked for
- People taking levothyroxine or levodopa need to separate them from iron
This is not a complete list of risks. Talk to a licensed clinician or pharmacist about your own situation. If you have a severe reaction, call 911. You can report side effects to the FDA through MedWatch at 1-800-FDA-1088.
Sources
- NIH ODS: Iron fact sheet for health professionals
- NIH ODS: Iron fact sheet for consumers
- 21 CFR 101.17(e): Required warning on iron-containing supplements (Cornell LII)
- MedlinePlus: Ferritin blood test
Also checked for this guide
- USPSTF: Screening and supplementation for iron deficiency and iron deficiency anemia during pregnancy (JAMA 2024)
- Stoffel et al.: Iron absorption from supplements given on consecutive vs alternate days in iron-depleted women (Lancet Haematol 2017)
Guide reviewed October 7, 2026.
Educational information only, not medical advice. It does not replace a conversation with a licensed clinician.
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