Iron Bisglycinate vs Ferrous Sulfate
Iron Bisglycinate and Ferrous Sulfate compared on absorption, gut tolerance, and real cost per dose — the cheapest of each pulled live from the Amazon US catalog.
Updated July 2026
Side by side
| Attribute | Bisglycinate | Ferrous sulfate |
|---|---|---|
| GI tolerance | Gentle | Often nausea / constipation |
| Absorption | Good | Good (reference form) |
| Best use | Sensitive stomach | Budget, if tolerated |
| Active deals tracked | 6 | 6 |
| Cheapest cost per dose | $0.07 (per 36 mg) | $0.05 (per 325 mg) |
Bisglycinate (iron chelated to glycine) is well absorbed and far gentler on the gut; ferrous sulfate is effective and the reference form in studies, but its unabsorbed iron is what drives the classic GI side effects.
Which to avoid / caveats
- Ferrous Sulfateis often the cheaper option, but it’s the lower-absorption form here — Effective and the most-studied reference iron, but its unabsorbed portion is what drives the classic nausea and constipation.
- Compare cost per elemental / active content, not the compound milligrams printed on the label — a bigger number on the front can hide less of what you actually absorb.
- The cheapest sticker price isn’t always the best value: our “cheapest per dose” figures normalise price across bottle sizes, so a larger count only wins if it truly costs less per serving.
Elemental iron: Iron Bisglycinate vs Ferrous Sulfate
By weight, Iron Bisglycinate is about 24% elemental iron (~240 mg per 1,000 mg), while Ferrous Sulfate is about 20% (~200mg per 1,000 mg). A higher elemental percentage isn’t automatically the better buy — a well-absorbed low-percentage form can beat a poorly-absorbed high-percentage one, so weigh this against absorption above and compare the “iron” line in the Supplement Facts panel, not the number on the front of the bottle.
It’s also why the per-serving costs above aren’t strictly comparable per milligram of elemental iron: some labels state the elemental amount while others list the heavier salt weight (so a bigger “mg” number can actually be less iron). For a true per-elemental-mg comparison, divide the price by the elemental milligrams shown on the Supplement Facts panel.
Iron BisglycinateWell absorbed
Best for: Sensitive stomachs and anyone who could not tolerate sulfate.
Best Iron Bisglycinate by cost per doseFerrous SulfateModerate absorption
Best for: Lowest cost and proven efficacy when tolerated.
Best Ferrous Sulfate by cost per doseCheapest Iron Bisglycinate
NEW
🩸 Iron Bisglycinate
Nutricost, Iron Chelate From Ferrochel, 36 Mg, 240 Caps
Cost per serving
$0.07
240 servings · ~240-day supply
Well absorbed
$15.95last seen · confirm on Amazon
HerbsPro 0
See the offer Cheapest Ferrous Sulfate
NEW
🩸 Ferrous Sulfate
21st Century, Iron Ferrous Sulfate, 325 mg, 120 Tabs
Cost per serving
$0.05
Cheap·−78%120 servings · ~120-day supply
Moderate absorption
$5.88last seen · confirm on Amazon
HerbsPro 0
See the offer Frequently asked
Is iron bisglycinate gentler than ferrous sulfate?+
Yes — bisglycinate is a chelated form that causes markedly less nausea and constipation than ferrous sulfate while still raising iron levels. It is the usual recommendation for people who could not tolerate sulfate.
Which iron should I take if sulfate upsets my stomach?+
Switch to a gentler chelated form such as iron bisglycinate, take it with vitamin C to aid absorption, and keep it away from calcium and coffee. Only supplement iron if you are actually low — excess iron is harmful.
Is Iron Bisglycinate or Ferrous Sulfate cheaper per dose?+
The cheapest Iron Bisglycinate we track is $0.07 per serving; the cheapest Ferrous Sulfate is $0.05 per serving — so Ferrous Sulfate costs less per dose right now (July 2026).
Is Iron Bisglycinate or Ferrous Sulfate higher in elemental iron?+
By weight, Iron Bisglycinate is about 24% elemental iron (~240 mg per 1,000 mg) and Ferrous Sulfate is about 20% (~200 mg per 1,000 mg). A higher elemental percentage isn't automatically better value — absorption differs by form, so weigh the "iron" line in the Supplement Facts panel against price and absorption, not the front-label number.
How much Iron do you need per day?+
Recommended Dietary Allowances range from 8 to 27 mg for adults, depending on age, sex, and life stage. Adult men get 8 mg; women 19–50 need 18 mg; women 51+ get 8 mg. Pregnancy is 27 mg and lactation 9 mg. People on vegetarian diets need 1.8 times more. — per the NIH Office of Dietary Supplements; general information, not medical advice.
Can you take too much Iron?+
Yes. The Tolerable Upper Intake Level is 45 mg for adults (40–45 mg for children). High-dose supplements can cause gastric upset, constipation, nausea, abdominal pain, vomiting, and diarrhea. Acute intakes over 20 mg/kg can cause corrosive necrosis of the intestine; extremely high doses can cause organ failure, coma, convulsions, and death. — per the NIH Office of Dietary Supplements; general information, not medical advice.
Dosage & safety answers sourced from the NIH Office of Dietary Supplements. General information, not medical advice.
What the research says
The risk of iron overload from dietary sources is low among adults with normal intestinal function, but high doses of iron supplements can cause gastrointestinal effects such as gastric upset, constipation, nausea, vomiting, and diarrhea, and extremely high doses can be severe, including corrosive necrosis of the intestine, multisystem organ failure, and even death. The Tolerable Upper Intake Level for iron is 45 mg for adults, and it ranges from 40 mg to 45 mg for infants, children, and adolescents, depending on age. — per the NIH Office of Dietary Supplements.
Although most people in the United States obtain adequate iron, pregnant women, infants and young children, women with heavy menstrual bleeding, frequent blood donors, and people with conditions such as cancer, gastrointestinal disorders, or heart failure are at risk of inadequate intakes. Iron deficiency anemia, which occurs when iron stores are exhausted and hemoglobin declines, can cause gastrointestinal disturbances, weakness, fatigue, and difficulty concentrating, and may impair cognitive function, immune function, and body temperature regulation; in infants and children it can cause psychomotor and cognitive abnormalities that may be irreversible. — per the NIH Office of Dietary Supplements.
Related
Best Iron Bisglycinate by cost per doseBest Ferrous Sulfate by cost per doseIron Bisglycinate dosage & factsFerrous Sulfate dosage & factsSupplement price-spread study
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References & sources
- Health Professional fact sheet — NIH Office of Dietary Supplements
- USP Verified product participants — U.S. Pharmacopeia
- NSF certified products — NSF
We link primary sources and paraphrase their findings — never copy their text, tables, or images. Cost-per-dose figures are our own first-party catalog data.