Supplement analysis backed by scientific evidence · PT · ES · DE · FR

← All supplements
Moderate evidenceVitamins & minerals

Iron Bisglycinate

The one premium iron form with a real meta-analysis behind it: in pregnant women it raised haemoglobin more than conventional iron salts and cut gastrointestinal side effects by roughly two thirds. In children the same analysis found no advantage, so the benefit is population-specific rather than universal.

View on iHerb Ships to 180+ countries · welcome discount for new customers

What the science says

  • Higher haemoglobin and fewer GI side effects in pregnancy Moderate evidence

    A systematic review and meta-analysis of 17 RCTs found that in pregnant women, 4-20 weeks of ferrous bisglycinate produced higher haemoglobin than other iron supplements (SMD 0.54 g/dL, 95% CI 0.15-0.94) and fewer gastrointestinal adverse events (incidence rate ratio 0.36, 95% CI 0.17-0.76). Tolerability is the more reliable of the two benefits and the one that matters most for adherence.

  • No demonstrated advantage in children, and ferritin gains were not significant Limited evidence

    In the same meta-analysis, the four paediatric trials showed no significant difference in haemoglobin or ferritin versus other iron supplements, and the ferritin trend in pregnant women did not reach significance. Iron stores — the outcome that determines whether treatment actually worked — remain the weakest part of the case.

  • Comparable results at lower elemental doses, but the evidence base is modest Limited evidence

    Trials commonly matched 25-30 mg elemental iron as bisglycinate against 60-100 mg as ferrous sulfate, which is where the tolerability advantage largely comes from. An independent 2024 review of oral iron formulations concluded that the comparative trial evidence for newer formulations is limited and that superiority over cheap iron salts is not established; a 2012 trial in cancer patients with mild anaemia is typical — positive, but small.

Dosage & safety

Studied dose14-30 mg elemental iron per day for treatment or repletion of iron deficiency; ferrous bisglycinate is roughly 20% elemental iron, so a 100 mg salt dose supplies about 20 mg elemental. Alternate-day rather than daily dosing improves fractional absorption by blunting the hepcidin response and is increasingly preferred. Take away from tea, coffee, calcium and dairy; vitamin C is not required with bisglycinate the way it helps with sulfate.
SafetyConstipation, dark stools and nausea still occur, though less often than with ferrous sulfate. Iron overdose is one of the leading causes of fatal poisoning in young children — keep bottles closed and out of reach. Contraindicated in hereditary haemochromatosis and other iron-overload states; do not supplement iron without a confirmed ferritin or haemoglobin indication. Iron reduces absorption of levothyroxine, tetracyclines, quinolones, bisphosphonates and levodopa (separate by 2-4 hours), and proton pump inhibitors reduce iron absorption. Not banned in sport.

How to take it

TimingAlternate-day dosing absorbs better than daily by blunting the hepcidin response, and is increasingly preferred.
With food?Best on an empty stomach; take it with a little food if nausea is the alternative to not taking it at all.
Worth knowingNever supplement iron without a ferritin or haemoglobin result — and keep the bottle closed and out of reach, because iron is a leading cause of fatal poisoning in young children.

Interactions

With medications

  • levothyroxine

    iron binds levothyroxine and markedly reduces its absorption separate by at least 4 hours

  • tetracycline and quinolone antibiotics

    mutual chelation reduces absorption of both separate by 2–4 hours

  • bisphosphonates

    iron blocks their already poor absorption separate by at least 2 hours

  • levodopa and methyldopa

    iron chelates them and reduces their effect separate by at least 2 hours

  • proton pump inhibitors and H2 blockers

    less gastric acid means less iron absorption expect slower repletion and discuss dosing with your prescriber

With other supplements

  • calcium supplements

    calcium competes with iron for absorption take them at different times of day

  • zinc supplements

    high doses of each reduce absorption of the other separate by at least 2 hours

  • vitamin C

    vitamin C enhances iron absorption, though bisglycinate depends on it less than ferrous sulfate does take together if you want the boost; it is not required with this form

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Is iron bisglycinate better than ferrous sulfate?

In pregnancy, yes, with moderate evidence: a meta-analysis of 17 trials found iron bisglycinate raised haemoglobin more than other iron supplements and cut gastrointestinal side effects by roughly two thirds. In children it showed no advantage, and ferritin gains were not significant.

Does iron bisglycinate cause constipation?

Iron bisglycinate can still cause constipation, dark stools and nausea, but less often than ferrous sulfate. Better tolerability is its most reliable advantage.

How should I take iron bisglycinate?

Take 14-30 mg of elemental iron as iron bisglycinate, ideally on alternate days, which improves absorption by blunting the hepcidin response. Take it away from tea, coffee, calcium and dairy, and only with a confirmed ferritin or haemoglobin indication.

Can I take iron bisglycinate with levothyroxine?

Iron bisglycinate markedly reduces levothyroxine absorption, so separate them by at least 4 hours. Also separate it by 2-4 hours from tetracycline and quinolone antibiotics.

Scientific references

Where to buy

Thorne, Iron Bisglycinate, 60 Capsules (25 mg per Capsule)

View on iHerb

Ships to 180+ countries · welcome discount for new customers

Referral link — this site may earn a commission on purchases.

Related in Vitamins & minerals