Reacted iron is a form of iron supplement where the iron has been chemically bonded (chelated) to amino acids, specifically glycine. The most common product sold under this name, made by Ortho Molecular Products, contains 29 mg of elemental iron as ferrous bisglycinate. The “reacted” label refers to the chelation process itself: the iron has already reacted with amino acids to form a stable compound, rather than existing as a simple iron salt like ferrous sulfate or ferrous fumarate.
How Chelated Iron Differs From Regular Iron
Standard iron supplements use inorganic iron salts. Ferrous sulfate, the most commonly prescribed form, is just iron bound to a sulfate molecule. These forms break apart in the stomach, releasing free iron ions that can irritate the gut lining and compete with other minerals for absorption.
Ferrous bisglycinate works differently. Each iron atom is wrapped in two glycine molecules, forming a small structure that behaves more like a protein fragment than a free metal. This allows the iron to pass through the stomach without releasing as many free ions, which is why it tends to cause fewer digestive problems. Some research suggests iron-amino acid chelates can enter intestinal cells through multiple routes, including the same transporters used for small protein fragments, rather than relying solely on the single transporter that handles free iron.
Absorption and Effectiveness
Manufacturers often claim that ferrous bisglycinate has roughly twice the bioavailability of traditional iron salts. In practice, this means you can take a lower dose and still get meaningful results. A trial in pregnant women found that 25 mg of iron from ferrous bisglycinate prevented iron deficiency anemia just as effectively as 50 mg from ferrous sulfate, with bisglycinate adequate to prevent anemia in more than 95% of Danish women through pregnancy and postpartum.
The picture isn’t always that clean, though. A randomized trial of 480 Cambodian women compared 18 mg of ferrous bisglycinate against 60 mg of ferrous sulfate over 12 weeks. The ferrous sulfate group ended up with higher iron stores: ferritin levels reached 99 micrograms per liter in the sulfate group versus 84 in the bisglycinate group. At that particular dose ratio (roughly one-third the amount), the chelated form didn’t fully match standard iron. The takeaway is that bisglycinate is more efficiently absorbed milligram for milligram, but the dose still matters. Taking too little of any form won’t fully correct a deficiency.
Why People Choose It: Fewer Side Effects
The main reason people seek out reacted iron is stomach trouble with regular supplements. Standard iron is notorious for causing constipation, nausea, and dark stools, and these side effects lead many people to stop taking their supplements entirely.
A randomized trial in pregnant women compared ferrous bisglycinate to ferrous fumarate (another common iron salt) and found dramatic differences in tolerability. Constipation occurred in about 7% of women taking bisglycinate versus 68% in the standard iron group. Nausea hit 7% versus 47%. Abdominal pain affected roughly 4% compared to 40%. A separate pregnancy trial confirmed the pattern, finding significantly fewer gastrointestinal complaints and less frequent black stools in the bisglycinate group compared to ferrous sulfate.
These differences make chelated iron a practical choice for anyone who has tried standard supplements and couldn’t stick with them. If you can’t tolerate the supplement, it doesn’t matter how cheap or effective it is on paper.
Who Benefits Most
Reacted iron is particularly popular among pregnant women, people with sensitive stomachs, and anyone with confirmed iron deficiency who has struggled with other forms. Pregnancy is a common scenario because iron needs increase significantly, but morning sickness and digestive sensitivity make standard iron supplements hard to tolerate. The clinical data showing that lower doses of bisglycinate can match the effectiveness of higher-dose iron salts is especially relevant here.
People with inflammatory bowel conditions or chronic digestive issues also tend to gravitate toward chelated iron, since free iron in the gut can worsen inflammation and feed certain bacteria. By keeping more of the iron bound to amino acids during transit, bisglycinate may reduce this effect.
Dosage and Safety Considerations
The branded Reacted Iron product provides 29 mg of elemental iron per capsule. The tolerable upper intake level set by the NIH is 45 mg of elemental iron per day for adults. This limit applies to all forms of iron and is based on the threshold where gastrointestinal side effects become common in healthy people. Physicians sometimes recommend doses above this level for treating diagnosed iron deficiency anemia, but that’s a clinical decision based on blood work.
One thing to keep in mind: “reacted” or “chelated” doesn’t mean the iron is risk-free at any dose. Iron is still iron, and excess amounts accumulate in the body. The chelation simply changes how efficiently it’s absorbed and how well your gut handles it. If you’re taking iron without a confirmed deficiency, you’re more likely to overshoot your needs regardless of the form.
How It Compares to Other Gentle Forms
Ferrous bisglycinate isn’t the only iron supplement marketed as easy on the stomach. Iron polysaccharide complex and carbonyl iron are also positioned as gentler alternatives. What sets bisglycinate apart is the stronger clinical evidence for both bioavailability and tolerability, particularly the head-to-head trials against standard forms showing meaningful reductions in side effects at doses that still correct deficiency.
You’ll sometimes see ferrous bisglycinate sold under other brand names or as a generic chelated iron. The “Reacted Iron” label is specific to Ortho Molecular Products, but the active ingredient is the same ferrous bisglycinate chelate available from multiple manufacturers. If you’re comparing products, check the amount of elemental iron per serving rather than the total weight of the chelate compound, since the glycine molecules add weight without contributing iron.