Iron Supplement Labels: Bisglycinate vs Ferrous Sulfate Wording, mg, %DV and the Overdose Warning
An iron bottle puts a form name on the front, such as bisglycinate, ferrous sulfate or ferrous gluconate, and a number such as 25 mg. The Supplement Facts panel and the warning box on the back tell you what that number covers, how it compares with the Daily Value and what the law makes every iron capsule bottle print. This guide reads one label line by line, using Thorne Iron Bisglycinate as the worked example. For the panel as a whole, start with our guide to reading a supplement label.
How we wrote this: label details come from the bottle images and text on the Thorne Iron Bisglycinate product page and from the NIH Dietary Supplement Label Database record DSLD 321969, read in October 2026. The warning rule is 21 CFR 101.17(e). The Daily Value comes from the FDA page on the Daily Value on the Nutrition and Supplement Facts labels, and the upper limit from the National Academies iron chapter. The NIH Office of Dietary Supplements iron fact sheet returned an access error when we checked, so we do not quote it or compare iron forms. Arithmetic marked as ours is simple division. We read labels; we did not test any product.
The short answer
Read the form name in parentheses after “Iron”, then the iron amount on that line, then the %DV printed next to it. Find the boxed accidental overdose warning, which every iron capsule or tablet label must carry. Check servings per container, Other Ingredients and any seal printed on the bottle. Treat the %DV and the upper limit as reference figures, not instructions.
Step 1: The form name, bisglycinate vs ferrous sulfate vs gluconate
The form is the compound the iron comes in. 21 CFR 101.36(d) lets a label name that source in parentheses right after the nutrient, preceded by “as” or “from”. When it does, the source does not have to be listed again in the ingredient statement.
Thorne’s bottle reads “Iron (as Ferrochel® Ferrous Bisglycinate Chelate)†”, and a boxed footnote says the product uses Albion’s Ferrochel Ferrous Bisglycinate Chelate, a registered trademark of Albion International. The ingredient list on the same web page shortens the line to “Iron (Bisglycinate)”. On other bottles the same spot may read ferrous sulfate, ferrous gluconate, ferrous fumarate or another name. Read that word on every bottle you compare so you know which form you are buying.
The words about the form are Thorne’s. The page calls it “a well-absorbed form of iron that reduces gastrointestinal side effects”, asks “Why is iron bisglycinate gentle on the stomach?” in its FAQ, and compares it with ferrous sulfate. Each of those claims carries an asterisk that points to the FDA disclaimer, which says the statement has not been evaluated by the Food and Drug Administration. We do not compare the forms ourselves. If the form matters to you, ask your doctor or pharmacist.
Bisglycinate is a word you also meet on magnesium bottles. Our magnesium form and elemental amount guide reads that label.
Step 2: Iron mg per serving
On Thorne’s bottle the line shows 25 mg against Iron, with the form in parentheses. Thorne’s FAQ says each capsule provides 25 mg of elemental iron from Ferrochel. The DSLD record lists the same 25 mg per 1 capsule.
When you compare bottles, compare the iron figure on the line that names iron. If a label you are looking at gives a weight for the whole compound rather than for iron, the two numbers are not the same thing, and the brand is the one to ask. We do not give conversion figures between forms.
Step 3: %DV and the Daily Value
The FDA lists the Daily Value for iron as 18 mg. Thorne’s bottle prints 139% in the %DV column, and the DSLD record lists that figure for adults and children 4 or more years of age. By our arithmetic, 25 mg divided by 18 mg is about 139%, so the printed figure matches.
- It is arithmetic. The %DV compares one serving with the Daily Value. It is not a recommendation for you personally.
- It follows the serving. Thorne’s serving size is one capsule, and the suggested use reads: “Take 1 capsule daily or as recommended by your health-care practitioner.”
- It adds up across products. Iron also appears in many multivitamins. Add the iron line from every panel you take to see your total. Our multivitamin label guide shows where it sits on a longer panel.
Step 4: The upper limit, as the source states it
The National Academies report on Dietary Reference Intakes states: “The Tolerable Upper Intake Level (UL) for adults is 45 mg/day of iron, a level based on gastrointestinal distress as an adverse effect.” The same chapter sets 40 mg/day for infants and children through 13 years of age.
The UL is a reference figure from that report, not a target and not advice from us. If you take more than one product with iron, add up the iron lines and take the total to your doctor or pharmacist.
Step 5: The accidental overdose warning
Under 21 CFR 101.17(e), any dietary supplement in solid oral dosage form, such as tablets or capsules, that contains iron or iron salts for use as an iron source must carry this statement:
WARNING: Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6. Keep this product out of reach of children. In case of accidental overdose, call a doctor or poison control center immediately.
The rule says the warning must appear prominently on the information panel, be set off in a box by hairlines, and appear on any labeling that contains warnings. Thorne’s bottle prints it in a box, worded this way:
WARNING: Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under six. Keep this product out of reach of children. In case of accidental overdose, call a doctor or a poison control center immediately.
Two small wording differences show up side by side: the bottle spells out “six” where the rule uses the numeral, and it adds “a” before “poison control center”. The DSLD record shows the bottle wording. Below the warning, a second box says Certification of Conformity of the child-proof closure with the Poison Prevention Packaging Act is available on Thorne’s site.
On any iron bottle, look for this box before anything else. If a capsule or tablet product lists iron and you cannot find the warning, ask the brand.
Step 6: Capsule count, other ingredients and seals
Thorne lists 60 capsules and 60 servings per container. At one capsule a serving, by our arithmetic, that is 60 servings. Other Ingredients on the bottle read: Hypromellose (derived from cellulose) capsule, Microcrystalline Cellulose, Leucine, Silicon Dioxide. The web page lists the same four in a different order.
The bottle prints an NSF Certified for Sport mark, a gluten free mark and “Manufactured in the USA using US & imported ingredients”. The web page adds dairy free and soy free. A seal counts when it is printed on your bottle or the certifier lists that exact product; our NSF Certified for Sport guide explains how to check.
Step 7: Other warnings and the disclaimer
Thorne’s page lists an allergy warning that the product is contraindicated for anyone with a history of hypersensitivity to any of its ingredients. The bottle says: “If pregnant, consult your health-care practitioner before using this product.” Under interactions, the page says there are no known adverse interactions or contraindications at publication date. Read these as the brand’s label statements.
Talk to your doctor or pharmacist before starting iron or any supplement, especially if you take medication or other products that list iron.
Our zinc supplement label guide reads a Thorne capsule panel with the same layout.
A quick checklist
- Form: the words in parentheses after Iron.
- Amount: the iron figure on that line, in mg.
- %DV: arithmetic against 18 mg, printed next to the amount.
- Upper limit: a reference figure from the National Academies, not a target.
- The boxed accidental overdose warning.
- Servings per container, Other Ingredients and printed seals.
- Allergy, pregnancy and interaction statements, as the label words them.
FAQ
What is the Daily Value for iron?
The FDA lists it as 18 mg. Thorne prints 139% for its 25 mg capsule, which matches our arithmetic.
Why does every iron bottle have the same warning?
21 CFR 101.17(e) requires it on iron supplements in solid oral dosage form, set off in a box.
Is Thorne Iron Bisglycinate NSF Certified for Sport?
The bottle prints the NSF Certified for Sport mark. Check NSF’s own listing for the exact product you buy.
These statements have not been evaluated by the Food and Drug Administration. The products mentioned are not intended to diagnose, treat, cure, or prevent any disease. Talk to a healthcare professional before starting a supplement.