Confused b/w choosing right type of iron for your body? Here’s the complete guide
Now-a-days there are present different forms of iron supplements in the market. Some suits your body and don’t cause any gastro side effects and some causes a number of gastrointestinal issues like constipation, abdominal pain, diarrhea, and nausea etc.
Having such symptoms after taking any supplement can make you leave that supplement immediately, that can make your body deficient of that supplement.
So, what to do in such a situation?????????
The answer is the shift to some other form/salt of that supplement like in the current case we have different forms of iron that is available in the market. So, if we are having side effects with one form of iron we can switch to the other form.
Here is a complete guide for the selection of the right type of iron supplement that suit your body and meet your body’s need without causing any side effect!!
Type of Iron Supplements in the Market:
First let’s look at which salt forms of iron are available in the market.
There are basically 2 natures of iron supplements which are are ferrous (Fe2+) salts and ferric (Fe3+) complexes. Other types include carbonyl iron and heme iron polypeptide
Types of Iron Supplements | Amount of elemental iron,* mg per tablet |
1. Ferrous Salts |
|
· Ferrous sulphate | 65 |
· Ferrous gluconate | 35 |
· Ferrous fumarate | 100 |
2. Ferric complexes |
|
· Ferrous bislgycinate | 50 |
· Ferric polysaccharide | 150 |
· Ferric polymaltose | 100 |
· Iron protein succinylate | 40 (may vary in different products & countries |
· Ferric citrate | 210 |
· Ferric maltol | 30 |
· Liposomal iron | 30 |
3. Other Forms |
|
· Carbonyl iron | 18 |
· Heme iron polypeptide | 12 |
Ferrous Salts:
Ferrous salts are the most common oral iron supplements that are prescribed due to the low cost and efficient recovery of iron deficiency. However due to the side effect profile that are sometimes replaced by the other forms of iron. Following are the most commonly available iron/ferrous salts in the market:
- Ferrous sulphate
- Ferrous fumarate
- Ferrous gluconate
Ferrous Sulfate (Iron (II) Sulfate):
Ferrous sulphate also known as iron sulfate is one of the most commonly used salt of iron that is widely available at a very low cost. It is highly prescribed iron supplements to treat the low level of iron in the body.
💊 Uses:
- It is considered as the first-line treatment for iron deficiency anemia (IDA).
- Iron sulfate is commonly used in pregnancy, menstruation-related anemia, and general IDA.
✅ Advantages:
Following are the top most advantages of ferrous sulphate:
- It is Inexpensive and widely available.
- Proven efficacy in raising haemoglobin and ferritin
⚠️ Disadvantages:
The main disadvantages of ferrous sulfate supplements are as follow:
- Gastrointestinal side effects are common:
- Nausea
- Epigastric discomfort
- Constipation
- Metallic taste
- Black stained teeths
- It can change the color of the stool to black, which is harmless but often afraid the patients.
- Patients often discontinue the supplements due to these gastrointestinal side effects.
⚕️Food interactions of ferrous sulfate:
- Avoid co-administration of dairy products like milk or yogurt etc with ferrous sulphate supplements. Take ferrous sulfate at least 2 hours before or after milk and other dairy products.
- Limit caffeine intake. Food and caffeine containing beverages may reduce iron absorption.
- Give a gap of at least 2 hours before or after calcium supplements.
- Don’t take it with antacids. Take ferrous sulfate at least 2 hours before or after antacids.
- Take with food. This may reduce gastric irritation. However, iron supplement performed better on empty stomach
- Take with foods containing vitamin C or vitamin c containing supplement can increase the absorption of the iron.
❌INTERACTION WITH OTHER MEDICATIONS:
This product can decrease the absorption of other drugs such as:
- bisphosphonates (for example, alendronate)
- levodopa
- penicillamine
- quinolone antibiotics(for example, ciprofloxacin, levofloxacin)
- thyroid medications (for example, levothyroxine)
- tetracycline antibiotics (for example, doxycycline, minocycline).
Ferrous Fumarate:
Ferrous fumarate is highly similar to the ferrous sulfate especially in the term of uses, side effects and interaction profile. However, it does have some advantages over ferrous sulfate which are mentioned as below:
✅ Advantages:
- High elemental iron content per dose.
- Requires fewer tablets compared to ferrous sulfate for the same iron dose.
- Cost-effective and available in generic formulations.
⚠️ Disadvantages:
- Higher iron content per tablet may worsen GI discomfort in sensitive patients.
FERROUS GLUCONATE:
- Ferrous gluconate is often recommended for elderly patients, children, or patients with GI disorders as it contains low iron content per tablet. It possesses following benefits which are as follow:
✅ Advantages:
- Better gastrointestinal tolerability than ferrous sulfate and fumarate.
- Lower incidence of constipation, nausea, and abdominal discomfort.
- Can be used in mild to moderate iron deficiency anemia or as a maintenance therapy after correction of iron levels.
⚠️ Disadvantages:
- As it contains Lower elemental iron content per tablet i.e. 35mg/tablet so, it requires more tablets to reach desired iron levels.
- Ferrous gluconate is also Less effective in severe anemia unless it is taken in higher doses.
- Like other ferrous salts, its absorption is decreased by food and antacids.
💡 Notes:
Often used when ferrous sulfate is not tolerated
⚕️Interaction profile is similar to the other ferrous salts.
⚕️IRON-FOOD AND IRON-MEDICINES INTERACTIONS ARE SAME IN ALL IRON/FERROUS SALTS!
Ferric Complexes/Iron complexes:
An iron complex/Ferric complex is a chemical compound where an iron atom is bonded to other molecules or ions (called ligands), forming a specific geometric structure having characteristic properties that effect their solubility, absorption and stability. It also modulate the side effect profile of the conventional form of iron supplements.
Following are the iron/ferric complexes that are available in the market:
- Iron bisglycinate
- Iron polysaccharide
- Iron polymaltose
- Iron protein succinylate
- Iron/ferric citrate
- Iron/Ferric maltol
Let’s discuss the pros and cons of each of them :
Ferrous/Iron bisglycinate (Chelated Ferrous Complex)
🔬 Composition:
Iron/ferrous bisglycinate is composed of Ferrous (Fe²⁺) salt bound to two glycine molecules in a chelate ring structure. chelated iron is protected from binding to dietary inhibitors like phytates (in grains), tannins (in tea), or calcium whose binding inhibits iron absorption. Thus chelated/complexes of iron have less drug interactions as compared to the normal iron/ferrous salts.
🩸 Absorption:
Its has at least two folds greater bioavailability than ferrous salts; absorbed via amino acid transporters, less affected by inhibitors like phytates
💊 Uses:
Iron bisglycinate is also among those iron forms that are widely present in multivitamin and other supplements. It is often recomended to treats iron deficiency anaemia in pregnancy, children, and GI-sensitive individuals
✅ Advantages:
Iron bisglycinate is gentle on the stomach, has fewer GI side effects and effective at lower doses .
⚠️ Disadvantages:
Mild GI effects possible (nausea, constipation); may interact with some medications. It is many folds expensive than the normal iron supplements containing iron/ferrous salts like ferrous sulphate, ferrous gluconate, and ferrous fumarate etc.
Ferric/Iron Polysaccharide Complex
🔬 Composition:
Iron polysaccharide is composed of ferric iron (Fe³⁺) encapsulated in a starch/dextran-based polysaccharide shell.
🩸 Absorption:
Iron polysaccharide shows slow absorption pattern, has enzyme-dependent release in the small intestine; moderate bioavailability (~30–40%) .
💊 Uses:
Iron polysaccharide is ideal for chronic anemia and usually chosen for better GI tolerance especially in individuals having gastrointestinal disorders
✅ Advantages:
Iron polysaccharide is gentle on the GI tract due to controlled iron release .
⚠️ Disadvantages:
Iron polysaccharide shows lower iron availability thus requires higher doses to meet needs and fulfil iron deficiency in the patient.
Ferric/Iron Polymaltose
🔬 Composition:
Iron polymaltose is composed of ferric hydroxide stabilized with polymaltose (carbohydrate) shell.
🩸 Absorption:
Iron polymaltose shows controlled release pattern in intestine thus reducing GI irritation. It has moderate absorption rate.
💊 Uses:
Iron polymaltose is suitable for patients who cannot tolerate ferrous salts. It is also available in syrup form for the treatment of iron deficiency in children.
✅ Advantages:
Iron polymaltose possess very low GI side effects.
⚠️ Disadvantages:
Iron polymaltose has lower bioavailability due to which it requires longer time for the recovery of iron level and consequently the treatment may take longer.
Iron Protein Succinylate (IPS)
🔬 Composition:
Iron protein succinylate is composed of ferric iron bound to succinylated milk-derived protein (casein). This process of succinylation modifies the protein to make it more soluble in less acidic environment of small intestine, rather than stomach.
🩸 Absorption:
Iron protein succinylate is resistant to stomach acid, soluble in small intestine; absorbed as Fe³⁺ → Fe²⁺ via DMT1 (Divalent metal transporter 1, a transporter protein that is involved in the transport of iron and other divalent metal ions within the cell. It is found in intestine, liver, and brain.)
💊 Uses:
Iron protein succinylate is used in GI-sensitive patients, such as those with ulcers or elderly individuals.
✅ Advantages:
Minimal gastric irritation; well tolerated as less free iron is released in stomach which minimizes the irritation to the stomach lining as free iron in the stomach can produce free reactive oxygen specie leading to inflammation.
⚠️ Disadvantages:
Iron protein succinylate has moderate absorption and is less widely available.
Ferric/Iron Citrate
🔬 Composition:
Iron citrate is formed by the complexation of Ferric iron with citrate.
🩸 Absorption:
Iron citrate has moderate absorption. It is also used intravenously in CKD to reduce phosphate . In the acidic pH of stomach, ferric ion dissociates from iron citrate/ferric citrate and forms complexes with phosphate anions creating insoluble precipitates, which don’t get absorbed in the bloodstream and thus eliminates from the body. Some ferric ions also get reduced to Fe²⁺ and are absorbed via divalent metal transporter 1 (DMT1).
💊 Uses:
Iron/ferric citrate is used in the treatment of iron deficiency anemia in CKD and as a phosphate binder. It is recommended to take iron/ferric citrate along with food.
✅ Advantages:
Iron citrate has dual action i.e. reduces phosphate level and can improve iron status.
⚠️ Disadvantages:
GI side effects possible; dosing may be limited by phosphate control
Ferric/Iron Maltol
🔬 Composition:
Iron/ferric maltol is composed of Ferric (Fe³⁺) ion bound to maltol (3-hydroxy-2-methyl-4-pyrone) which is a naturally occuring molecule often used as a flavor enhancer.
🩸 Absorption:
Stable complex of iron maltol enhances solubility and intestinal absorption However, iron gets dissociated from the maltol complex prior to absorption, while free maltol is absorbed separately, metabolized, and excreted in
urine.
💊 Uses:
Iron maltol is approved for the treatment of iron-deficiency anemia. It is recommended to take it on empty stomach at least 1 hour before or 2
hours after meals. It can be used during inactive IBD (inflammatory bowel disease) (i.e. patient is not currently having IBD symptoms) and CKD (Chronic kidney disease)
✅ Advantages:
Iron maltol has comparatively better tolerability.
⚠️ Disadvantages:
Iron maltol can cause GI upset (flatulence, diarrhea), can flare the symptoms of active IBD (IBD flare.) and it is contraindicated with iron overload. Iron maltol is more expensive than other iron forms .
Liposomal Iron
🔬 Composition:
Iron (often ferric pyrophosphate or ferrous bisglycinate) encapsulated in phospholipid liposomes forms liposomal iron. The phospholipid shell merges with the intestinal cell membrane (enterocytes) through endocytosis, delivering iron directly inside the cells.
🩸 Absorption:
Liposomal iron has high (up to 90%) absorption rate occurring via endocytosis and bypasses DMT1 and is acid-independent thus effective in the patients with impaired iron absorption (chronic inflammation) or gastric issues. Liposomes inhibits the oxidation and degradation of the iron contents in the core & helps in targeted delivery of the iron.
Through “Trojan Horse-like” mechanism, the liposomes are absorbed directly in the intestinal lumen by the microfold cells (M cells) of the small intestine, which is infact the part of the lymphatic system. Subsequently, the liposomes are incorporated in macrophages through the process of endocytosis and through the lymphatic system reaches hepatocytes. Upon entering the hepatocytes, the liposomes are opened by lysosomal enzymes, as a result of this, iron is released and becomes available for the utilization.
💊 Uses:
liposomal iron is Indicated for patients intolerant to conventional iron, with absorption issues or on acid suppressants.
✅ Advantages:
liposomal iron shows higher and faster absorption, minimal GI side effects, acid resistance, and ease of use . Not affected by the dietary inhibitors like phytates unlike other conventional forms of iron. Also available in oro-dispersable sachets
⚠️ Disadvantages:
Liposomal iron is more expensive than the conventional form of iron and it has fewer long-term studies.
OTHER FORMS OF IRON:
Other forms of iron includes the following:
- Carbonyl iron
- Heme Iron Polypeptide (HIP)
So, let’s discuss what specialties do they possess:
Carbonyl Iron
🔬 Composition:
Highly pure elemental iron (~98–100%) formed via thermal decomposition of iron pentacarbonyl.
🩸 Absorption:
Carbonyl iron is slowly dissolved in acid in order to convert to ferrous ion and has moderate bioavailability (~30–40%) .
💊 Uses:
Carbonyl iron is used to treats and prevents iron deficiency in individuals sensitive to GI side effects as it dissolves slowly so, it delivers iron at a slow rate and thus causes minimal side effects.
✅ Advantages:
Carbonyl iron has low GI irritation comparatively and also possess lower overdose risk.
⚠️ Disadvantages:
Carbonyl iron has slow absorption pattern due to which it is less effective in the treatment of severe anemia.
Heme Iron Polypeptide (HIP)
🔬 Composition:
Heme iron polypeptide is derived from hemoglobin (heme-bound iron) in animal sources. Heme iron is naturally present in animal products like meat, fish, and poultry, is more readily absorbed by the body However, Non-heme iron is present in plant-based foods and fortified foods and is absorbed less efficiently.
Absorption of non-heme iron is affected by other components present in the diet like vitamin C (which enhances absorption) and calcium (which can inhibit absorption)
🩸 Absorption:
Heme iron polypeptide is absorbed intact via heme transporters and is converted to Fe²⁺ inside intestinal cells. It is highly independent of GI pH.
💊 Uses:
Heme iron polypeptide is used when conventional iron is not tolerated or poorly absorbed. Show to be effective in correcting iron deficiency in patients with CKD however, is inferior to the intravenous iron therapy in CKD patients
✅ Advantages:
Heme iron polypeptide causes less GI irritation and works even with dietary inhibitors.
⚠️ Disadvantages:
Heme iron polypeptide is more expensive than the conventional iron supplements. It is derived from animal source due to which it not suitable for vegetarians/vegans. Less evidence compared to standard forms
Final Message!
So, as we see that there are different type of iron that are available in market. Ferrous salts have good efficacy and absorption but also causes gastrointestinal side effects, while most of ferric complexes have less gastro side effects but are slow in restoring iron level in body and require longer treatment duration.
Doctor’s perspective:
“Doctors often recommend ferrous salts like ferrous sulfate, ferrous gluconate or ferrous fumarate due to their high efficacy and absorption as well as low price, However if the patient couldn’t tolerate the gastrointestinal side effects and is not suffering from severe anemia as well then they go for ferric complexes or other forms of iron.”
As a result of all this discussion we need to look for the patient’s body need, the side effect profile of the iron form that we are going to use, how rapid we want out patient’s iron level to restore to the optimal level and personal preferences as well, before choosing any form of iron.
References:
Pantopoulos, K. (2024). Oral iron supplementation: New formulations, old questions. Haematologica. Advance online publication. https://doi.org/10.3324/haematol.2024.284967
DrugBank. (n.d.). Ferrous sulfate anhydrous (DB13257). DrugBank. Retrieved July 5, 2025, from https://go.drugbank.com/drugs/DB13257
Fischer, J. A. J., Cherian, A. M., Bone, J. N., & Karakochuk, C. D. (2023). The effects of oral ferrous bisglycinate supplementation on hemoglobin, ferritin, and gastrointestinal adverse events: A systematic review and meta-analysis. Nutrition Reviews. Advance online publication. https://doi.org/10.1093/nutrit/nuac106
Maladkar, M., Sankar, S., & Yadav, A. (2020). A novel approach for iron deficiency anaemia with liposomal iron: Concept to clinic. Journal of Biosciences and Medicines, 8(9), 27–41. https://doi.org/10.4236/jbm.2020.89003
Gordeuk, V. R., Brittenham, G. M., McLaren, C. E., Hughes, M. A., & Keating, L. J. (1986). Carbonyl iron therapy for iron deficiency anemia. Blood, 67(3), 745–752. https://doi.org/10.1182/blood.V67.3.745.745
Disclaimer:
This comparison is for informational and educational purposes only. It does not substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting any iron supplementation.
