Iron Bisglycinate vs Ferrous Sulphate: Which Is Gentler, and How to Take Iron

If you've ever taken iron tablets, there's a fair chance you remember them for the wrong reasons: constipation, nausea or an upset stomach. Those side effects are the main reason people stop taking iron before their levels have recovered.

That's why iron bisglycinate has become popular as an alternative to ferrous sulphate, the iron most commonly prescribed in Ireland and the UK. This guide explains the difference between the two, what the evidence shows, and how to take iron so it works and is easier to tolerate.

What iron does

Iron contributes to the normal formation of red blood cells and haemoglobin, the normal transport of oxygen in the body, the reduction of tiredness and fatigue, normal energy-yielding metabolism, normal cognitive function and the normal function of the immune system.

Iron deficiency is common, especially in women with heavy periods, during pregnancy, in people who don't eat meat, frequent blood donors and endurance athletes. Iron from meat and fish (haem iron) is absorbed better than iron from plants (non-haem iron).

Ferrous sulphate

Ferrous sulphate is an iron salt. It is inexpensive, well studied and effective, which is why it is the standard first choice. Its drawback is tolerability: free iron in the gut can irritate the stomach and bowel lining, and gastrointestinal side effects such as constipation, nausea and stomach pain are common.

Iron bisglycinate

Iron bisglycinate is iron bound to two molecules of the amino acid glycine, forming a chelate. The bond keeps the iron stable as it passes through the stomach and reduces how much free iron interacts with the gut lining and with substances in food that block absorption.

What the evidence suggests:

• Several trials, many in pregnant women, have found iron bisglycinate raised haemoglobin and ferritin at least as well as iron salts, often at lower doses of elemental iron.
• The same studies generally report fewer gastrointestinal side effects.
• A systematic review of trials in pregnancy found that iron bisglycinate was associated with higher haemoglobin and fewer gastrointestinal side effects than other iron supplements, while noting that the evidence was of low certainty and more good-quality trials are needed.

So bisglycinate is a reasonable choice for people who struggle with standard iron, while ferrous sulphate remains effective and much cheaper.

How to take iron so it works

• Consider every-other-day dosing. Taking iron raises a hormone called hepcidin that reduces iron absorption for about a day afterwards. Studies have found that taking iron on alternate days can improve the fraction absorbed and may reduce side effects. Ask your GP whether this suits you.
• Take it on an empty stomach if you can, or with a small amount of food if it upsets your stomach.
• Pair it with vitamin C, such as a glass of orange juice or fruit, which helps non-haem iron absorption.
• Keep tea and coffee away from iron by at least an hour; their polyphenols block absorption.
• Space it from calcium, dairy, antacids and zinc or magnesium supplements, which compete with iron.
• Separate it from certain medicines, including levothyroxine and some antibiotics. Ask your pharmacist about timing.
• Be patient and retest. Haemoglobin usually rises within weeks, but rebuilding iron stores (ferritin) takes months. Your GP will usually recheck bloods to confirm it's working.

Side effects and safety

• Dark or black stools are normal with iron.
• If side effects are a problem, talk to your GP before stopping; options include changing the form, lowering the dose or alternate-day dosing.
• Keep iron supplements out of reach of children. Iron overdose is a leading cause of serious poisoning in young children.
• People with haemochromatosis, a common genetic condition in Ireland that causes iron overload, should not take iron supplements unless specifically advised.
• If a blood test doesn't show deficiency, don't take iron just in case.

When to see your GP

Iron deficiency always has a cause, such as heavy periods, diet, pregnancy, or blood loss from the gut. Your GP may look for the reason, particularly if you're male, post-menopausal, or have changes in bowel habits. Don't self-treat ongoing tiredness without getting it checked.

Key takeaways

• Only take iron if a blood test shows you need it.
• Ferrous sulphate is effective and cheap but often causes stomach side effects.
• Iron bisglycinate is a chelated form that trials suggest is at least as effective and generally gentler, though more high-quality research is needed.
• Alternate-day dosing, vitamin C, and keeping tea, coffee and calcium apart can all help absorption.
• Keep iron away from children, and retest to confirm your levels have recovered.

Our NeuroThrive™ Iron Bisglycinate provides 20 mg of iron as ferrous bisglycinate per capsule.

Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. This article is for general information and is not medical advice.