Iron

How long does it take for iron supplements to work?

Updated 9 Nov 2026

Short answer

Hemoglobin can rise within weeks. In a trial of adults with iron deficiency anemia who took 100 mg of iron three times a day, it rose by 1.84 g/dL after 2 weeks.[1] Raising the iron stores took longer in athletes: 16 to 100 mg a day raised blood iron markers over 6 to 8 weeks, and shorter courses did not.[2] In a fatigue trial, women took 80 mg a day for 12 weeks, and the authors suggest checking blood markers after 6 weeks.[3]

Sources (3)

  1. The Efficacy and Safety of Vitamin C for Iron Supplementation in Adult Patients With Iron Deficiency Anemia: A Randomized Clinical Trial. Li N, Zhao G, Wu W, Zhang M, Liu W, Chen Q, et al. JAMA Netw Open, 2020. PMID 33136134
  2. Effects of Oral Iron Supplementation on Blood Iron Status in Athletes: A Systematic Review, Meta-Analysis and Meta-Regression of Randomized Controlled Trials. Šmid AN, Golja P, Hadžić V, Abazović E, Drole K, Paravlic AH Sports Med, 2024. PMID 38407751
  3. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. Vaucher P, Druais PL, Waldvogel S, Favrat B CMAJ, 2012. PMID 22777991

More about iron

What is iron?Which foods contain iron?What is iron used for?What are the signs of iron deficiency?Is iron safe?Does iron help with tiredness?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.