Disclosure: We earn commissions on purchases made through our links. This never influences our scores. Editorial policy
Iron (Bisglycinate)
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 Nature Made Iron 65mg (Ferrous Sulfate) (94/100), about $0.02 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.
If a blood test has confirmed you are low on iron and the standard iron pill tears up your stomach, bisglycinate is the form you want.
- Evidence
- Strong Evidence
- Category
- Vitamins & Minerals
- Best form
- ferrous bisglycinate chelate
- Effective dose
- 18mg elemental iron daily for maintenance (RDA for premenopausal women)
- Lab tested
- 7 of 8 products
- Category
- Vitamins & Minerals
- Best form
- ferrous bisglycinate chelate
- Effective dose
- 18mg elemental iron daily for maintenance (RDA for premenopausal women)
- Lab tested
- 7 of 8 products
Key takeaways
- →Works for confirmed deficiency, full stop. Bisglycinate matches ferrous sulfate's hemoglobin gains with meaningfully fewer GI side effects.
- →Maintenance is 18mg elemental; anemia treatment runs 50-65mg under medical guidance. Take fasted with vitamin C, away from coffee, dairy, and calcium.
- →Thorne ($0.33/day, NSF Certified for Sport) is the top pick; NOW Foods Iron Bisglycinate 36mg ($0.12/day) is the value option.
- →Never supplement without a ferritin test - iron has no excretion route, and excess causes oxidative damage. Separate from levothyroxine by 4 hours.
What Is Iron (Bisglycinate)?
If a blood test has confirmed you are low on iron and the standard iron pill tears up your stomach, bisglycinate is the form you want. When you are actually deficient, the case for iron is not in doubt - it rebuilds hemoglobin and ferritin (your stored iron) and clears the fatigue and brain fog that come with running low. You are not alone here either: iron deficiency affects an estimated 2 billion people, and it lands hardest on pregnant women, menstruating women, and anyone whose ferritin is already low. The one rule that overrides everything else: do not start iron without a blood test. Your body has no way to dump extra iron back out, so men and postmenopausal women should only take it once ferritin confirms they truly need it.
Where the form really earns its keep is your gut. Ferrous sulfate is the standard, decades-old form doctors reach for, and it leaves a lot of people nauseated, constipated, and crampy. Put the two head to head and iron bisglycinate moves your iron numbers about as well while causing far fewer of those problems. That is the whole pitch for bisglycinate: it works about as well, and it is much easier to live with.
The reason it is gentler comes down to chemistry. "Chelated" just means each iron atom is wrapped in two glycine (an amino acid) molecules. That wrapping shields the iron from the things in food that normally grab it and block absorption (phytates, tannins, calcium), and it lets the iron come in through a route that irritates your gut less. It absorbs nearly as well as ferrous sulfate on an empty stomach, and better when you take it with food.
One point worth repeating, because it is the part people skip: do not supplement iron unless a test has shown you are deficient. Extra iron has nowhere to go, so it builds up and causes oxidative damage over time. Men and postmenopausal women rarely need it at all and should only supplement if blood work says so. The number to ask for is serum ferritin - your iron stores, not just a standard blood count - and it is worth checking both before you start and while you are taking it.
Does It Work? The Evidence
How A-F grades workIron (Bisglycinate) earns a Strong Evidence rating on the strength of its best-supported use: treatment of iron-deficiency anemia (confirmed by blood test) (grade A). The table below grades every claimed benefit on its own, including weaker and more heavily marketed uses, so one strong result never stands in for the rest.
Treatment of iron-deficiency anemia (confirmed by blood test)
Pasricha et al. Cochrane Review 2013; WHO iron supplementation guidelines; multiple large RCTs in women and children
Bisglycinate form: fewer GI side effects vs. ferrous sulfate
Tolkien ZJ, et al. PLOS ONE 2015 (n=90 RCT); Name JJ, et al. Int J Vitam Nutr Res 2018 (systematic review)
Reducing fatigue in non-anemic iron deficiency (low ferritin, normal hemoglobin)
Vaucher P, et al. CMAJ 2012 RCT (n=198); Favrat B, et al. Blood 2011 - fatigue improved with ferritin normalization
Cognitive function in iron-deficient adolescents and women
Murray-Kolb LE, Beard JL. Am J Clin Nutr 2007; Bruner AB, et al. Lancet 1996 - improved attention and memory in iron-deficient adolescent girls
Athletic performance improvement in iron-deficient athletes
Burden RJ, et al. Br J Sports Med 2015 meta-analysis; improvements in VO2 max and endurance in iron-deficient (not just anemic) athletes
Hair loss due to iron deficiency
Trost LB, et al. J Am Acad Dermatol 2006 review - association between low ferritin and telogen effluvium; causality not firmly established in RCTs
Iron supplementation in replete individuals (no deficiency)
No RCTs support iron supplementation in iron-sufficient individuals; risk of harm from excess iron is established
| Grade | Claimed Benefit | Key Studies | Our Verdict |
|---|---|---|---|
| A | Treatment of iron-deficiency anemia (confirmed by blood test) | Pasricha et al. Cochrane Review 2013; WHO iron supplementation guidelines; multiple large RCTs in women and children | Supported |
| B | Bisglycinate form: fewer GI side effects vs. ferrous sulfate | Tolkien ZJ, et al. PLOS ONE 2015 (n=90 RCT); Name JJ, et al. Int J Vitam Nutr Res 2018 (systematic review) | Supported |
| B | Reducing fatigue in non-anemic iron deficiency (low ferritin, normal hemoglobin) | Vaucher P, et al. CMAJ 2012 RCT (n=198); Favrat B, et al. Blood 2011 - fatigue improved with ferritin normalization | Early Signal |
| B | Cognitive function in iron-deficient adolescents and women | Murray-Kolb LE, Beard JL. Am J Clin Nutr 2007; Bruner AB, et al. Lancet 1996 - improved attention and memory in iron-deficient adolescent girls | Early Signal |
| B | Athletic performance improvement in iron-deficient athletes | Burden RJ, et al. Br J Sports Med 2015 meta-analysis; improvements in VO2 max and endurance in iron-deficient (not just anemic) athletes | Early Signal |
| C | Hair loss due to iron deficiency | Trost LB, et al. J Am Acad Dermatol 2006 review - association between low ferritin and telogen effluvium; causality not firmly established in RCTs | Conflicted |
| F | Iron supplementation in replete individuals (no deficiency) | No RCTs support iron supplementation in iron-sufficient individuals; risk of harm from excess iron is established | Ineffective |
How to Choose: Forms, Doses & What Matters
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.
Best forms: ferrous bisglycinate chelate, iron bisglycinate, ferrous sulfate (standard clinical form, lower GI tolerance), ferrous fumarate, carbonyl iron
You absorb the most iron on an empty stomach - 30-60 minutes before a meal, or 2 hours after one. The catch is that an empty stomach is also when iron is most likely to make you feel queasy. Bisglycinate is easier on the gut than ferrous sulfate, so this is a smaller problem, but it is still real. If you cannot stomach it fasted, taking it with a little food is a fair trade. Pair it with vitamin C. A 100-200mg dose of vitamin C (ascorbic acid) taken at the same time helps your body hold iron in the ferrous (Fe2+) form, the one it absorbs more easily. This is well established and recommended by the NIH, and a small glass of orange juice does the job just as well as a vitamin C pill. Keep a 2-hour gap between iron and a few things that fight it: dairy and calcium supplements (calcium competes directly for the same absorption), coffee and tea (their tannins and polyphenols cut absorption by 40-90%), phytate-rich foods like whole grains and legumes, and the medications listed above. Consider taking it every other day instead of daily. Emerging evidence suggests alternate-day dosing may work about as well for some people while causing fewer side effects, and it can be easier on your wallet. In a 2017 study in Blood, Stoffel et al. found you actually absorb a higher fraction of each dose on alternating days, because spacing it out keeps hepcidin (the hormone that throttles iron uptake) from clamping down. Do not push the dose higher on your own. A typical course for iron-deficiency anemia runs 3-6 months, with ferritin and hemoglobin rechecked at 4-8 weeks and again when you finish. Keep going for at least 3 months after your hemoglobin looks normal - that is the stretch that refills your stores rather than just topping off the surface.
Who Should Take Iron (Bisglycinate)?
The honest answer is short: take iron only if a blood test has confirmed you are low. The tests that tell you are serum ferritin (the most sensitive read on your iron stores), hemoglobin and hematocrit (which catch anemia), and sometimes transferrin saturation and total iron binding capacity (TIBC) for a fuller picture. If you are in one of the groups below, you are more likely to come back low - but the test still comes first. You menstruate heavily. This is the single most common reason people run low on iron in developed countries. The average cycle loses 20-80ml of blood; once you are past 80ml, your stores can drain even when you are eating well. You are pregnant. Iron demand nearly doubles in pregnancy, because your body is building extra red blood cells, feeding the placenta, and growing a baby. The NIH puts the target at 27mg elemental iron daily, and supplementing is routine. You are caring for an infant or toddler, especially one born premature. Fast growth on top of low iron reserves at birth puts these little ones at real risk. Your gut does not absorb well. Celiac disease, Crohn's disease, gastric bypass surgery, and H. pylori infection all get in the way of pulling iron from food. You donate blood often. Each whole-blood donation draws down your stores, which is why the American Red Cross suggests frequent donors keep an eye on ferritin. You train hard, especially endurance or female athletes. You lose iron through sweat, through the pounding of foot-strike, and through small amounts of GI bleeding - and that often meets a diet that was already running thin. You eat plant-based. Plant (non-heme) iron is the only kind in a vegan or vegetarian diet, and your body absorbs far less of it than the heme iron in meat.
Who Should Avoid It?
Not for everyone
Side Effects & Safety
Product Scores
8 products scored on dosing accuracy, third-party testing, cost per effective dose, and label transparency.
The Scorecard: 8 Products Compared
Nature Made Iron 65mg (Ferrous Sulfate)
Nature Made$7.06 ÷ 353 days at 65mg/day (1 serving × 65mg)
Included as a comparison reference point. USP Verified and extremely cheap. The catch: ferrous sulfate causes GI side effects (nausea, constipation) in 30-70% of users. If you tolerate it, it is equally effective to bisglycinate at a fraction of the cost. If you do not tolerate it, bisglycinate is the answer.
Prices checked 2026-06-09. Cost shown is per clinically effective daily dose, not per pill.
Thorne Iron Bisglycinate
Thorne$16.00 ÷ 59 days at 25mg/day (1 serving × 25mg)
NSF Certified for Sport makes this the top choice for competitive athletes and anyone prioritizing certification rigor. Clean capsule with minimal excipients.
Prices checked 2026-06-09. Cost shown is per clinically effective daily dose, not per pill.
Pure Encapsulations Iron-C
Pure Encapsulations$14.00 ÷ 61 days at 15mg/day (1 serving × 15mg)
Built-in vitamin C is a meaningful practical advantage. The go-to option for people with food allergies or multiple sensitivities. Practitioner-grade quality.
Prices checked 2026-06-09. Cost shown is per clinically effective daily dose, not per pill.
Solgar Gentle Iron 25mg
Solgar$16.60 ÷ 184 days at 25mg/day (1 serving × 25mg)
Uses Albion FERROCHEL - the most clinically studied iron bisglycinate chelate form. A meaningful distinction for those who want the exact form used in trials.
Prices checked 2026-06-09. Cost shown is per clinically effective daily dose, not per pill.
NOW Foods Iron Bisglycinate 36mg
NOW Foods$9.27 ÷ 93 days at 36mg/day (1 serving × 36mg)
The most cost-effective bisglycinate option in this comparison. Good choice for budget-conscious buyers who do not require NSF or USP certification.
Prices checked 2026-06-09. Cost shown is per clinically effective daily dose, not per pill.
MegaFood Blood Builder
MegaFood
$23.99 ÷ 60 days at 26mg/day (1 serving × 26mg)
The only product in this comparison with a brand-specific clinical trial. NSF Content Certified. The beet root and whole-food matrix are marketing differentiators without established clinical superiority over plain bisglycinate.
Prices checked 2026-06-09. Cost shown is per clinically effective daily dose, not per pill.
Garden of Life mykind Organics Iron
Garden of Life$9.99 ÷ 30 days at 18mg/day (1 serving × 18mg)
Limited to the RDA dose (18mg) and uses a proprietary blend that obscures the iron form. Adequate for maintenance in non-deficient people but not appropriate for treating iron-deficiency anemia.
Prices checked 2026-03-01. Cost shown is per clinically effective daily dose, not per pill.
Flora Floradix Iron + Herbs Liquid Formula
Flora
$41.42 ÷ 50 days at 10mg/day (1 serving × 10mg)
Popular with pregnant women and those who cannot swallow capsules. The 10mg per serving dose is too low for deficiency treatment - would require multiple servings daily to reach therapeutic range, making cost very high. Better suited for maintenance than repletion.
Prices checked 2026-06-09. Cost shown is per clinically effective daily dose, not per pill.
Full Comparison
| Category | Nature Made Iron 65mg (Ferrous Sulfate) Nature Made | Thorne Iron Bisglycinate Thorne | Pure Encapsulations Iron-C Pure Encapsulations | Solgar Gentle Iron 25mg Solgar | NOW Foods Iron Bisglycinate 36mg NOW Foods | MegaFood Blood Builder MegaFood | Garden of Life mykind Organics Iron Garden of Life | Flora Floradix Iron + Herbs Liquid Formula Flora |
|---|---|---|---|---|---|---|---|---|
| Brand Score | 94/100Winner | 94/100 | 92/100 | 90/100 | 88/100 | 79/100 | 76/100 | 58/100 |
| Dosing & Form | 25/25Winner | 25/25 | 22/25 | 25/25 | 25/25 | 25/25 | 25/25 | 18/25 |
| Purity | 22/25 | 25/25Winner | 23/25 | 20/25 | 20/25 | 20/25 | 19/25 | 17/25 |
| Value | 25/25Winner | 21/25 | 22/25 | 23/25 | 23/25 | 15/25 | 15/25 | 8/25 |
| Transparency | 22/25 | 23/25 | 25/25Winner | 22/25 | 20/25 | 19/25 | 17/25 | 15/25 |
| Cost/Day | $0.02Winner | $0.27 | $0.23 | $0.09 | $0.10 | $0.40 | $0.33 | $0.83 |
| Dose/Serving | 65mg | 25mg | 15mg | 25mg | 36mg | 26mg | 18mg | 10mg |
| Form | ferrous sulfate tablet | ferrous bisglycinate chelate capsule | iron bisglycinate + aspartate, 175mg ascorbic acid, hypoallergenic capsule | iron bisglycinate chelate (Albion FERROCHEL), vegetable capsule | iron bisglycinate chelate vegetable capsule | ferrous bisglycinate chelate + whole-food cofactors, tablet | iron from organic plant blend (form unspecified), tablet | ferrous gluconate liquid with herbal extracts |
| Third-Party Tested | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | No |
| Proprietary Blend | No | No | No | No | No | No | Yes | Yes |
Frequently Asked Questions
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 $30 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.
Should I take vitamin C with my iron supplement?
Yes, and this is a well-supported strategy. Vitamin C (ascorbic acid) keeps iron in the ferrous (Fe2+) state, which is more readily absorbed by intestinal cells than the ferric (Fe3+) state. Taking 100-200mg of vitamin C simultaneously with your iron supplement increases non-heme iron absorption. This works with any iron form. A small glass of orange juice with your iron supplement is a practical way to do this. Note that this benefit matters more for ferrous sulfate than for bisglycinate, since bisglycinate's chelation already partially protects against absorption inhibitors.
Can vegans and vegetarians get enough iron from diet alone?
It is possible but requires deliberate effort. Plant foods contain only non-heme iron, which has 2-5 times lower bioavailability than the heme iron found in meat, poultry, and fish. Additionally, plants high in iron (legumes, whole grains, spinach) often contain phytates and oxalates that further reduce iron absorption. The NIH recommends that vegetarians consume 1.8 times the standard iron RDA due to lower bioavailability. Good plant iron sources include lentils, tofu, tempeh, pumpkin seeds, quinoa, fortified cereals, and dark leafy greens. Pairing them with vitamin C-rich foods and avoiding coffee and tea at meals significantly improves absorption. Vegans and vegetarians should monitor ferritin levels, particularly if female or athletically active.
Related Supplements
Related Reading
Related Articles
Sources
- NIH Office of Dietary Supplements. Iron Fact Sheet for Health Professionals. Updated 2023.
- Tolkien ZJ, Stecher L, Mander AP, Pereira DI, Powell JJ. Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis. PLoS ONE. 2015;10(2):e0117383.
- Name JJ, Vasconcelos AR, Valzachi Rocha Maluf MC. Iron Bisglycinate Chelate and Polymaltose Iron for the Treatment of Iron Deficiency Anemia: A Pilot Randomized Trial. Curr Pediatr Rev. 2018;14(4):261-268.
- Pasricha SR, Flecknoe-Brown SC, Allen KJ, et al. Diagnosis and management of iron deficiency anaemia: a clinical update. Med J Aust. 2010;193(9):525-532.
- Stoffel NU, Cercamondi CI, Brittenham G, et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. Lancet Haematol. 2017;4(11):e524-e533.
- World Health Organization. Guideline: Daily iron supplementation in adult women and adolescent girls. Geneva: WHO; 2016.
- 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.
- Burden RJ, Morton K, Richards T, Whyte GP, Pedlar CR. Is iron treatment beneficial in, iron-deficient but non-anaemic (IDNA) endurance athletes? A systematic review and meta-analysis. Br J Sports Med. 2015;49(21):1389-1397.
Scores and tiers are our independent opinion, formed by applying a published rubric to label data, third-party certifications, and the research record. They are not statements of objective fact about a product and not a lab test. Where we report a brand-specific fact, it comes from a cited source or a public certification; where verification is missing, we say so rather than assume a result.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. The products discussed on this page are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before starting any supplement regimen.