Iron Bisglycinate vs Ferrous Sulfate: Why the Gentler Form Works Better

If you've been diagnosed with iron deficiency or anaemia, you've probably been prescribed ferrous sulfate — the standard HSE and NHS iron supplement. And there's a reasonable chance it made you constipated, nauseous, or gave you stomach cramps. You're not alone — GI side effects affect up to 50% of people on ferrous sulfate, and poor adherence as a result is the most common reason iron deficiency treatment fails.

Iron bisglycinate is a different form of iron that delivers the same therapeutic benefit with a fraction of the GI side effects. Here's why it works better and who should use it.

The Chemistry of Absorption

Ferrous sulfate delivers iron as an ionic iron molecule that must compete with other minerals (calcium, magnesium, zinc) for absorption in the gut, and that is directly irritating to the intestinal mucosa. The free iron ions produce oxidative stress in the gut lining, causing the inflammation that produces constipation, nausea, and cramping.

Iron bisglycinate (also called iron glycinate or ferrochel iron) delivers iron chelated — bonded — to two glycine molecules. This chelation protects the iron from interactions with other minerals and maintains it in a stable, absorbable form through the gut. The glycine chelate enters intestinal cells through peptide transport pathways rather than competing mineral channels, improving absorption and dramatically reducing gut irritation.

The Clinical Evidence

Multiple comparative studies have found that iron bisglycinate produces equivalent or superior increases in ferritin and haemoglobin to ferrous sulfate at the same or lower doses, with significantly fewer GI side effects. A 2001 study in pregnant women found that iron bisglycinate produced the same haematological outcomes as ferrous sulfate at half the dose, with dramatically lower rates of constipation and GI discomfort. The Cochrane review of iron bisglycinate in pregnancy found consistent evidence of superior tolerability compared to standard iron salts.

Who Should Use Iron Bisglycinate

Anyone with confirmed iron deficiency who experiences GI side effects on standard iron supplements. People with sensitive digestive systems, IBS, or inflammatory bowel conditions. Pregnant women, for whom GI comfort during iron supplementation significantly improves adherence. People taking iron long-term for chronic conditions or high-demand situations like endurance sport.

Iron supplementation should be based on confirmed deficiency through blood testing. Excess iron is harmful. Always consult your GP before beginning iron supplementation. NeuroThrive™ products are food supplements and are not intended to diagnose, treat, or cure any medical condition.