Disclosure: We earn commissions on purchases made through our links. This never influences our scores. Editorial policy
Best Iron Supplement (2026)
Clinical dose: 18mg elemental iron daily for maintenance (RDA for premenopausal women); 50-65mg elemental iron daily for treating documented iron-deficiency anemia. Dose must be confirmed by blood test.
Bottom line
In our scoring, Iron (Bisglycinate) rates strong evidence: the research is strong for treatment of iron-deficiency anemia. Our top-scored product is Thorne Iron Bisglycinate (94/100), about $0.27 a day at a clinical dose of 18mg elemental iron daily for maintenance. Bottom line: worth it for the right goal. This is our opinion, not medical advice; talk to your clinician before starting.
Our Top Picks
Thorne Iron Bisglycinate
$0.27/day at effective dose
Price checked 2026-06-09
NOW Foods Iron Bisglycinate 36mg
$0.10/day at effective dose
Price checked 2026-06-09
Pure Encapsulations Iron-C
$0.28/day at effective dose
Price checked 2026-06-09
We earn commissions on purchases made through our links. This never influences our scores or recommendations. See our editorial policy.
Related guides and head-to-heads
What to know first
If you have ever quit an iron supplement because it wrecked your stomach, you are not alone - the traditional forms (ferrous sulfate, ferrous fumarate) are notorious for constipation, nausea, and cramping. The good news is there is a gentler option. Iron bisglycinate (chelated iron) is better absorbed and causes significantly fewer of those gut side effects, which makes it the form most people should start with.
(If the nausea is the part you most want to settle, our ginger supplement picks cover the best-evidenced option for that.) We scored the top iron products across all forms with special attention to tolerability, dose accuracy, and whether the product includes absorption-enhancing co-factors like vitamin C. If you are pregnant, iron is one piece of a complete prenatal, so see our best prenatal vitamins guide.
For specific brand match-ups, see Thorne vs NOW Foods and Nature Made vs Thorne. Thorne Iron Bisglycinate is one product nothing we score beats on both score and cost; see the full split in Thorne alternatives.
The Verdict
The best iron supplement for most people is Thorne Iron Bisglycinate: a gentle, well-absorbed chelated form that is far easier on the stomach than ferrous sulfate, third-party tested (NSF Certified for Sport), at about $0.27 a day. The best value is NOW Foods Iron Bisglycinate 36mg at roughly $0.10 per day with the same gentle chelated form and third-party testing. For a verified option that pairs iron with vitamin C for absorption, Pure Encapsulations Iron-C is the quality pick at about $0.23 a day after a steep price drop.
One rule overrides all of this: iron is the one supplement you should take only if you actually need it. Confirm low iron with a ferritin blood test first, take it with vitamin C and away from coffee and calcium, and choose a bisglycinate form to minimize the constipation and nausea that drive most people off iron.
What the Evidence Says About Iron (Bisglycinate)
How A-F grades work- ATreatment of iron-deficiency anemia (confirmed by blood test)
- BBisglycinate form: fewer GI side effects vs. ferrous sulfate
- BReducing fatigue in non-anemic iron deficiency (low ferritin, normal hemoglobin)
- BCognitive function in iron-deficient adolescents and women
- BAthletic performance improvement in iron-deficient athletes
- CHair loss due to iron deficiency
- FIron supplementation in replete individuals (no deficiency)
A = strong RCT evidence · B = moderate · C = limited · D = weak · F = no evidence.
Detailed Reviews
Thorne Iron Bisglycinate
ferrous bisglycinate chelate capsule | 25mg/serving | 60 servings
Price checked 2026-06-09
NSF Certified for Sport makes this the top choice for competitive athletes and anyone prioritizing certification rigor. Clean capsule with minimal excipients.
Pure Encapsulations Iron-C
iron bisglycinate + aspartate, 175mg ascorbic acid, hypoallergenic capsule | 15mg/serving | 60 servings
Price checked 2026-06-09
Built-in vitamin C is a meaningful practical advantage. The go-to option for people with food allergies or multiple sensitivities. Practitioner-grade quality.
NOW Foods Iron Bisglycinate 36mg
iron bisglycinate chelate vegetable capsule | 36mg/serving | 90 servings
Price checked 2026-06-09
The most cost-effective bisglycinate option in this comparison. Good choice for budget-conscious buyers who do not require NSF or USP certification.
Also Scored
MegaFood Blood Builder
$0.40/day | ferrous bisglycinate chelate + whole-food cofactors, tablet
Price checked 2026-06-09
Full score breakdownGarden of Life mykind Organics Iron
$0.33/day | iron from organic plant blend (form unspecified), tablet
Price checked 2026-03-01
Full score breakdownFlora Floradix Iron + Herbs Liquid Formula
$1.49/day | ferrous gluconate liquid with herbal extracts
Price checked 2026-06-09
Full score breakdownNature Made Iron 65mg (Ferrous Sulfate)
$0.02/day | ferrous sulfate tablet
Price checked 2026-06-09
Full score breakdownSolgar Gentle Iron 25mg
$0.09/day | iron bisglycinate chelate (Albion FERROCHEL), vegetable capsule
Price checked 2026-06-09
Full score breakdownProduct prices and availability are accurate as of the date indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply.
What to Look For When Buying
- ✓Iron bisglycinate (chelated iron) causes fewer GI side effects than ferrous sulfate while maintaining equivalent or better absorption
- ✓Do not supplement iron without a documented deficiency - excess iron accumulation is harmful and cannot be easily excreted
- ✓Vitamin C taken with iron increases absorption by 2-3x - some products include it, or take with orange juice
- ✓Take iron on an empty stomach for best absorption, but with food if it causes stomach upset
- ✓Avoid taking iron with calcium, dairy, coffee, or tea - all of these significantly reduce absorption
- ✓Slow-release formulations may cause fewer side effects but can have lower overall absorption
Frequently Asked Questions
How much iron bisglycinate should I take for anemia?
For documented iron-deficiency anemia, the range used clinically is 50-65mg of elemental iron daily; 18mg daily is the maintenance RDA figure for premenopausal women. Read the label for elemental iron, not the total compound weight, since those are different numbers. The part that overrides the dose question: iron is the one supplement you should take only when a blood test says you need it, so confirm low ferritin with your clinician and let them set the dose. Excess iron accumulates and is harmful, and there is no safe way to self-prescribe a treatment dose.
What is the difference between iron bisglycinate and ferrous sulfate?
Both supply elemental iron to treat deficiency, but they differ in tolerability and how they are absorbed. Ferrous sulfate is the classic clinical form - cheap, well-studied, and effective, but it releases ionic iron that directly irritates intestinal lining, causing nausea and constipation in 30-70% of users. Iron bisglycinate chelate binds each iron atom to two glycine amino acids. This protects the iron from binding to inhibitors in food (phytates, tannins, calcium) and allows it to be absorbed through a different intestinal pathway that causes far less irritation. A 2015 RCT by Tolkien et al. found bisglycinate produced equivalent increases in ferritin and hemoglobin to ferrous sulfate but with significantly fewer GI adverse effects. The tradeoff is cost - bisglycinate products typically cost 2-5x more per milligram of elemental iron.
Do I really need a blood test before taking iron supplements?
Yes - this is one of the most important safety points about iron. Unlike water-soluble vitamins that your body can simply excrete if you get too much, iron accumulates in the body. Excess iron generates oxidative damage to the liver, heart, and other organs. Iron overload disorders (including hereditary hemochromatosis, which affects 1 in 250 people of Northern European descent) can be worsened or unmasked by supplementation. Additionally, the correct dose depends entirely on your current iron status - a person with ferritin of 8 needs a very different approach than someone with ferritin of 12. A serum ferritin test costs under thirty dollars and gives you the information you need. Do not guess.
How long does it take for iron supplements to work?
Hemoglobin typically begins rising within 2-4 weeks of adequate iron supplementation, with a target of increasing by at least 1 g/dL in 4 weeks in those with true iron-deficiency anemia. Symptoms like fatigue and weakness often improve within 4-8 weeks as hemoglobin normalizes. However, replenishing iron stores (restoring ferritin to a healthy level) takes considerably longer - typically 3-6 months of continued supplementation after hemoglobin normalizes. Stopping supplementation as soon as you feel better is a common mistake that leads to relapse. Follow your doctor's guidance on duration and recheck ferritin at treatment completion.
Why do iron supplements cause constipation and how can I prevent it?
Constipation from iron is mainly caused by free ionic iron irritating the intestinal lining and altering gut motility. Several strategies reduce it: choose iron bisglycinate or carbonyl iron over ferrous sulfate; take with food (sacrifices some absorption but greatly improves tolerance); try alternate-day dosing (which also allows better absorption per dose according to 2017 research in Blood by Stoffel et al.); increase dietary fiber and fluid intake; and ensure adequate magnesium intake, which supports bowel motility. If constipation is severe and unresponsive to these measures, IV iron (given in a clinical setting) bypasses the GI tract entirely and is used in patients with severe intolerance or malabsorption.
Sources
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. Dietary supplements are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before starting any supplement regimen.