Iron Bisglycinate vs Ferrous Sulfate

Supplement Science Editorial Team·Evidence-Based Supplement Research

Published Apr 1, 2026

This content is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement. Full disclaimer

Iron bisglycinate is the better choice for most people — it causes dramatically fewer GI side effects and absorbs well...

Head-to-Head Comparison

Criteria	Iron Bisglycinate	Ferrous Sulfate	Winner
Bioavailability	High — chelated form resists absorption inhibitors	Moderate — well absorbed on empty stomach, inhibited by food	Iron Bisglycinate
Clinical Evidence	Moderate — growing head-to-head trials showing non-inferiority	Very Strong — gold standard in iron deficiency treatment for decades	Ferrous Sulfate
GI Tolerability	Excellent — dramatically fewer GI side effects	Poor — nausea, constipation, and stomach pain are common	Iron Bisglycinate
Cost	$0.15-0.30/serving	$0.03-0.08/serving	Ferrous Sulfate
Food & Drug Interactions	Low — chelation protects against most common inhibitors	High — inhibited by calcium, tea, coffee, dairy, antacids, and fiber	Iron Bisglycinate

Detailed Analysis

Bioavailability

Iron bisglycinate is chelated to two glycine molecules, protecting it from common absorption inhibitors like phytates, polyphenols, and calcium. Ferrous sulfate's absorption drops significantly when taken with food, tea, coffee, or calcium supplements.

Clinical Evidence

Ferrous sulfate is the form recommended by WHO guidelines and used in the vast majority of iron deficiency and anemia trials. It has the deepest evidence base for efficacy. However, bisglycinate head-to-head trials consistently show equivalent hemoglobin improvement at lower elemental doses.

GI Tolerability

GI side effects are the #1 reason patients discontinue iron supplements. Studies show ferrous sulfate causes GI complaints in 30-50% of users, while bisglycinate reduces this to under 10%. The chelated structure prevents free iron from irritating the gut lining.

Cost

Ferrous sulfate is extremely cheap and available generically at every pharmacy. Iron bisglycinate costs 3-5x more, though the price difference is still modest in absolute terms — typically $3-7 more per month.

Food & Drug Interactions

Ferrous sulfate must be taken on an empty stomach and separated from calcium, dairy, tea, coffee, and antacids by 2+ hours for optimal absorption. Iron bisglycinate's amino acid chelate shields it from most dietary inhibitors, allowing flexible dosing with meals.

Our Verdict

Iron bisglycinate is the better choice — far fewer GI side effects, flexible dosing with food, and equivalent efficacy at lower doses. Choose ferrous sulfate only if cost is the primary concern.

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Frequently Asked Questions

Can I take iron bisglycinate and ferrous sulfate together?

There's no reason to combine them. Pick one form based on your priorities: bisglycinate for tolerability, ferrous sulfate for cost. Taking both increases the risk of GI side effects and iron overload without additional benefit. Most adults need 18mg (women) or 8mg (men) of elemental iron daily.

Which iron form is better for anemia treatment?

Both effectively treat iron deficiency anemia. Head-to-head trials show bisglycinate achieves equivalent hemoglobin increases at lower elemental doses with far fewer side effects. Critically, better tolerability means patients actually finish their course — ferrous sulfate non-compliance due to GI issues is a major clinical problem.

Is iron bisglycinate worth the extra cost over ferrous sulfate?

For most people, absolutely. The extra $3-7/month buys dramatically better tolerability — fewer than 10% report GI issues versus 30-50% with ferrous sulfate. If you've tried ferrous sulfate and quit due to nausea or constipation, bisglycinate is the clear answer. The form you'll actually take consistently is the most effective one.

Can I take iron bisglycinate with food and coffee?

Yes — that's one of bisglycinate's biggest advantages. The amino acid chelate protects iron from common dietary inhibitors like phytates, tannins (in tea and coffee), and calcium. While absorption is still slightly better on an empty stomach, the reduction is far less than with ferrous sulfate. Taking it with food also further reduces the already-low risk of stomach discomfort.

References

Milman N, Jønsson L, Dyre P, Pedersen PL, Larsen LG (2014). Ferrous bisglycinate 25 mg iron is as effective as ferrous sulfate 50 mg iron in the prophylaxis of iron deficiency and anemia during pregnancy in a randomized trial. Journal of Perinatal Medicine. DOI PubMed
Coplin M, Schuette S, Leichtmann G, Lashner B (1991). Tolerability of iron: a comparison of bis-glycino iron II and ferrous sulfate. Clinical Therapeutics. PubMed