“Low iron causes fatigue even if you are not anemic.”
Low iron stores can cause tiredness even with a normal blood count; in trials, iron pills eased fatigue in tired women with low stores.
A normal blood count does not always mean your iron stores are fine, and low stores can leave you tired. A ferritin test answers the question better than guessing with a supplement.
If you have been tired for weeks, ask for a ferritin test along with a blood count before taking iron.
Safety note: Iron pills are dangerous for young children: accidental overdose of iron products is a leading cause of fatal poisoning in children under 6, so store them out of reach. Iron can block the absorption of some medicines, including thyroid medicine (levothyroxine) and antibiotics such as doxycycline and ciprofloxacin, so doses need to be spaced apart. Low iron without a clear reason, such as heavy periods or pregnancy, needs a check for hidden bleeding in the stomach or gut.
Talk to a healthcare professional if: you have been tired for weeks without a clear reason, you have low iron without heavy periods or pregnancy to explain it, or you take thyroid medicine or antibiotics and want to start iron.
Randomized trials in tired women with low iron stores but normal blood counts found that iron eased fatigue more than placebo, and a review of 18 trials agrees. Confidence is moderate because fatigue is self-reported, the trials are mostly in women, and measured exercise capacity did not improve.
Low iron stores can cause tiredness even with a normal blood count; in trials, iron pills eased fatigue in tired women with low stores. Iron did not improve measured exercise capacity, and the trials are mostly in women.
In a 2012 trial of 198 tired women aged 18 to 53 with low iron stores (ferritin below 50 micrograms per liter) but normal blood counts, iron pills for 12 weeks lowered fatigue scores by 47.7%, compared with 28.8% on placebo; quality of life, depression and anxiety did not change. A 2018 review of 18 trials in 1,170 adults with low iron but no anemia found less self-reported tiredness with iron but no clear gain in measured exercise capacity. Tiredness has many causes, so it does not by itself show that iron is low; a ferritin blood test helps check iron stores, though inflammation, infection and some other conditions can raise ferritin.
- Houston BL, Hurrie D, Graham J, Perija B, Rimmer E, Rabbani R, Bernstein CN, Turgeon AF, Fergusson DA, Houston DS, Abou-Setta AM, Zarychanski R. Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults: a systematic review of randomised controlled trials. BMJ Open. 2018;8(4):e019240. DOI: 10.1136/bmjopen-2017-019240. PMID: 29626044. PMCID: PMC5892776
- Vaucher P, Druais PL, Waldvogel S, Favrat B. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ. 2012;184(11):1247-1254. DOI: 10.1503/cmaj.110950. PMID: 22777991. PMCID: PMC3414597
- MedlinePlus, National Library of Medicine. Ferritin Blood Test. Medical tests. Last updated March 18, 2025
- U.S. Code of Federal Regulations. 21 CFR 101.17(e): Dietary supplements containing iron or iron salts. Via Cornell Legal Information Institute
- NHS. Taking ferrous sulfate with other medicines and herbal supplements. Page last reviewed 9 February 2023
- NHS. Iron deficiency anaemia: causes. Page last reviewed 26 January 2024