Ferrous Bisglycinate vs Ferrous Sulfate: Which Iron Is Gentler and Better?
Ferrous sulfate is the standard, inexpensive iron supplement and works well, but often causes constipation, nausea and stomach pain. Ferrous bisglycinate is a chelated form that in some trials raised hemoglobin at least as well at lower doses with fewer digestive side effects. If sulfate doesn't agree with you, bisglycinate is a reasonable switch. Only take iron if you need it.
Ferrous bisglycinate vs ferrous sulfate is the main choice most people face when buying iron. Iron supplements are essential when you're low, but many people quit because of stomach side effects. The form you choose can make a difference.
Side-by-side
| Ferrous bisglycinate | Ferrous sulfate | |
|---|---|---|
| Type | Iron bound to two glycine molecules (chelate) | Iron salt |
| Typical elemental iron per tablet | 25–36 mg | 65 mg (in a 325 mg tablet) |
| Digestive side effects | Fewer in several trials | Common: constipation, nausea, cramps |
| Evidence | Growing; a 2023 meta-analysis | Decades; standard of care |
| Cost | Higher | Very low |
What the research shows
A 2023 meta-analysis of randomized trials found that, in pregnant women, ferrous bisglycinate raised hemoglobin more and caused fewer gastrointestinal side effects than other iron salts, though the certainty of evidence was low. Other groups had less data.
Ferrous sulfate remains effective and is what most guidelines and studies use.
Tips for any iron supplement
- Only take iron if a blood test shows you need it. Too much iron is harmful, and iron overload conditions exist.
- Take it with vitamin C (or orange juice) to boost absorption.
- Keep it apart from calcium, tea, coffee and antacids by at least 2 hours.
- Separate it from levothyroxine and some antibiotics. Check our interaction checker.
- Store iron away from children. Iron overdose is dangerous for kids.
The verdict
Start with whatever your clinician recommends, often ferrous sulfate. If it causes side effects that make you stop, ferrous bisglycinate is a gentler alternative with reasonable evidence. Pairing iron with vitamin C helps either form; see how much vitamin C per day.
Frequently asked questions
Should I take iron every day or every other day?
Some research suggests taking iron on alternate days may improve absorption and tolerability. Follow your clinician's advice.
Should I take iron with vitamin C?
Vitamin C increases iron absorption. Taking iron with a source of vitamin C, and away from tea, coffee and calcium, helps.
Sources
This page is for education and is not a substitute for advice from your doctor. Read our medical disclaimer.