Ferrous Sulphate, Fumarate or Bisglycinate? A Guide to Iron

The Quick Verdict

• Ferrous Sulphate: If iron levels are found to be low following medical assessment, ferrous sulphate is commonly prescribed as a first-line treatment in the UK. Patient compliance is generally not very good, as some patients find it can be harsh on their stomach.
• The Gentle Iron: If gastrointestinal side effects are an issue, ferrous gluconate tablets or sodium feredetate liquid (Sytron) are often reported to be better tolerated.
• The Chelated Iron: errous bisglycinate is a newer form of iron that is absorbed more efficiently and is generally considered gentler on the digestive system. However, it is rarely prescribed and is more commonly found in supplements.
• OTC Iron: Be cautious with supermarket brands such as Spatone or Floradix. These products often contain very low doses (5mg–14mg), which may be insufficient where iron-deficiency anaemia has been formally diagnosed.

Disclaimer: This article is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. The information provided is general in nature and does not take into account your individual medical history or specific health conditions. Always consult a qualified healthcare professional, such as your GP or pharmacist, before starting, stopping, or changing any medication or supplement.

Why People Find It Hard To Take Iron?

In my daily practice, I dispense iron almost every single day. Iron deficiency anaemia is very common.

Symptoms include: fatigue, shortness of breath, and pale skin.

Treatment can be challenging. While effective, some standard iron tablets can be harsh on the digestive system. Many patients stop taking them simply because the side effects make them feel worse than the anaemia itself.

1. The Gold Standard: Ferrous Sulfate

When iron deficiency is diagnosed, ferrous sulphate is commonly prescribed as a first-line option. Ferrous sulphate is chosen because it is effective, inexpensive, and widely used. A typical 200mg tablet contains approximately 65mg of elemental iron.

Iron therapy is often continued for several months, with blood tests repeated to assess response. Continuation or discontinuation of treatment is determined by the prescriber based on blood results and clinical need.

The Downside Of Ferrous Sulfate

In my practice, I have seen significant number of patients report gastrointestinal side effects after taking the ferrous sulfate. If these effects are mild, treatment is often continued. However, some patients discontinue therapy when side effects significantly affect quality of life.

Constipation: The most frequently reported issue.

Nausea and stomach pain: Often occurring shortly after ingestion.

Dark stools: This is a recognised and generally harmless effect of oral iron. However, the presence of additional symptoms such as abdominal pain or visible blood should always be assessed by a healthcare professional.

2. Alternative Form Of Iron: Fumarate & Gluconate

Iron is also available as ferrous fumarate and ferrous gluconate. Ferrous fumarate is often used when ferrous sulphate is not tolerated. Ferrous fumarate comes in 210mg or 305mg tablets. It actually has more elemental iron per tablet than sulfate form (approx 68mg vs 65mg), although tolerability can vary between individuals.

Ferrous gluconate is generally considered the gentler option. It contains significantly less elemental iron per tablet (only about 35mg in a 300mg tablet). Because the dose of actual iron is lower, it tends to cause less stomach issues.

3. The Secret Iron: Sodium Feredetate

This is a form of iron that many patients and even some doctors overlook. It comes in a liquid form and you may know it by the brand name Sytron.

Why Sodium Feredetate Is Gentler?

Sodium feredetate breaks down differently in the gut compared to the other iron forms like sulphate. It releases iron in a way that is less likely to irritate the stomach lining.

Clinical data suggests that Sodium Feredetate is significantly better tolerated, causing fewer stomach issues. Some studies indicate it can be just as effective (if not better in some cases) at improving haemoglobin levels, potentially because patients actually keep taking it instead of stopping it due to side effects.

4. Ferrous Bisglycinate (Chelated Iron)

You likely won’t see this on a prescription, but you will see it in supplements.

Ferrous Bisglycinate is a form of iron where the iron molecule is “chelated” (bound) to two glycine molecules.

Why is it different? Because it is bound to glycine, it passes through the stomach more easily, reducing the gastro-intestinal side-effects.

The Benefits:

• Higher Absorption: Research indicates it may be 2-4 times more bioavailable than Ferrous Sulphate
• Fewer Side Effects: Because it is chelated and better absorbed, it is less likely to cause constipation or nausea in some users
• Less Food Interaction: Unlike Sulphate, Bisglycinate is less likely to be blocked by phytates (grains)

5. Over-The-Counter Iron: Spatone, Floradix & Others

Many people choose over the counter products like Spatone, Floradix, or supermarket Gentle Iron because they want to avoid side effects. These products are generally gentle, but doses vary widely.

The Dosage Gap: A prescription tablet generally gives you 65mg of iron per tablet.

• Spatone (Sachet): Typically contains only 5mg of iron.
• Floradix (Liquid): Typically contains around 7.5mg per 10ml dose.
• Supermarket “Gentle Iron”: Usually contains 14mg.

These lower-dose products may be suitable for maintenance or mild supplementation. They are generally not equivalent to prescription-strength iron used in the treatment of diagnosed iron-deficiency anaemia

Comparison Table: Know Your Dose

It can be confusing when the box says “200mg” or “300mg.” What matters is the Elemental Iron, the active amount your body actually gets.

Product / Iron Salt	Typical Strength	Elemental Iron (Approx.)	Pharmacist’s Verdict
Ferrous Sulfate	200mg Tablet	65mg	The standard. Strong and effective, but some people don’t tolerate it well
Ferrous Fumarate	210mg Tablet	68mg	Similar strength to sulfate. A common alternative to ferrous sulfate.
Ferrous Gluconate	300mg Tablet	35mg	The gentle tablet. Lower iron content, fewer side effects.
Sodium Feredetate	5ml Liquid	27.5mg	Good for tolerability, gentle on the stomach.
Ferrous Bisglycinate	Supplement	20-28mg	Best Bioavailability. Highly absorbable and very gentle, but more expensive.
OTC “Gentle Iron”	Tablet	14mg	Good for maintenance, but weak for treatment.
Floradix	10ml Liquid	7.5mg	Low dose. Tasty, but unlikely to cure anaemia quickly.
Spatone	1 Sachet	5mg	Very gentle but very low dose.

Iron Absorption: General Educational Information

Iron absorption can be influenced by timing, food, and other nutrients.

• Iron is absorbed more efficiently on an empty stomach
• Vitamin C can enhance iron absorption
• Taking iron with food may reduce absorption but can improve tolerability

These are general principles only.

Quick Summary

1. The Standard: Ferrous Sulphate is generally the first line.
2. Sodium Feredetate: Given if the sulfate or fumarate from is not tolerated. Generally, better tolerated.
3. Bisglycinate: Often better tolerated but usually not prescribed
4. Check the OTC Dose: If you buy products like Spatone, be aware they have very low doses (5mg) compared to prescription iron.

Medical & Safety Disclaimer

Educational Purpose Only – Not Medical Advice

The information provided here does not constitute a personal medical consultation, diagnosis, or prescription. Do not use this information to self-diagnose. If you suspect you have a medical problem, you must consult your General Practitioner or pharmacist.