Person Writing Fe Periodic


Ferralet-90 is a prescription-only iron product that contains two different types of iron:

  • Ferrous gluconate
  • Carbonyl iron

Ferrous sulfate is available over the counter and is the most commonly used form for supplementation.

The main points of differentiation between iron products are:

  • Percentage of elemental iron
  • Absorption rate
  • Tolerability
  • Cost

Below, I go into more detail regarding the comparison between Ferralet-90 and ferrous sulfate supplements, but as a general summary:

  • Ferralet-90 has both immediate-release and extended-release properties while ferrous sulfate is an immediate release product.
  • Per dose, Ferralet-90 will provide more iron than most ferrous sulfate products.
  • Studies indicate that both ferrous gluconate and carbonyl iron (both in Ferralet-90) may be better tolerated in terms of side effects than ferrous sulfate.
  • Ferrous sulfate products are, in most cases, significantly less expensive than Ferralet-90.
  • In addition to iron, Ferralet-90 contains additional ingredients, such as vitamin C and docusate (stool softener)

The side effect you mention experiencing (dizziness) typically is not associated with iron supplementation. Most commonly, adverse GI effects (e.g. nausea, vomiting, cramping) are most prevalent.

Dizziness may indicate you are actually not getting enough iron. You should be sure to contact your doctor and discuss the effects you are experiencing so you can be properly evaluated.

Section Summary
Ferrous sulfate is the most common form of supplemental iron available over the counter (OTC). Ferralet-90 is a prescription only product containing two forms of iron (ferrous gluconate and carbonyl iron) as well as additional ingredients. It may be better tolerated than ferrous sulfate but is more expensive.

Elemental Iron

Ferrous Sulfate

Ferrous sulfate contains 20% elemental iron by weight, which can lead to a misunderstanding regarding how some products are labeled.

A ferrous sulfate product that is labeled as '325 mg ferrous sulfate' actually contains 65 mg of elemental iron.


Ferralet-90 has two forms of iron:

  • Ferrous gluconate
  • Carbonyl iron

Ferrous gluconate contains 12% elemental iron by weight, which is less than ferrous sulfate.

Carbonyl iron is not an iron salt (e.g. the 'sulfate' in ferrous sulfate is the salt) but actually iron microparticles.

Carbonyl iron is 100% elemental iron as it is not an iron salt.

Section Summary
Ferralet-90 contains ferrous gluconate (12% elemental iron) for immediate release and carbonyl iron (100% elemental iron) that is sustained release. Ferrous sulfate contain 20% elemental iron.


Ferrous sulfate and ferrous gluconate are considered 'fast absorbing' iron products, but studies indicate that ferrous gluconate generally has slightly slower absorption. This may lend it to being better tolerated.

Nevertheless, the ferrous gluconate contained in Ferralet-90 is the 'fast absorbing' iron in the product.

Carbonyl iron is slow-absorbing as the gastric acid in our stomach must convert it (elemental iron) to the hydrochloride salt prior to absorption in the stomach. Therefore, the absorption rate of carbonyl iron is relatively slow and limited by gastric acid production.

Section Summary
Ferrous sulfate is immediate release and quickly absorbed while Ferralet-90 has both an immediate release and slow-release properties (from carbonyl iron).


Most studies indicate that the forms of iron in Ferralet-90 are better tolerated than ferrous sulfate. This may be due to the slower absorption or the fact that it includes ferrous gluconate, which contains less elemental iron than ferrous sulfate.

Carbonyl iron seems to be very well-tolerated and has a good safety profile, even at high doses. In fact, carbonyl iron may be less likely to cause iron overdoses due to its slow absorption.

Section Summary
Studies indicate that ferrous gluconate and carbonyl iron may be better tolerated than ferrous sulfate.


Ferrous sulfate and ferrous gluconate are most commonly recommended to treat iron-deficient anemia due to the low cost and well-established effectiveness. The cost typically ranges from $0.05-0.10 per day.

The cost of Ferralet-90 will vary depending on whether or not your insurance covers it (it is available by prescription only). Without insurance, it will cost around $70 for a 30 day supply (~$2.30 per day).

Section Summary
Ferrous sulfate is the least expensive iron product. The price of Ferralet-90, a prescription only product, will vary based on your insurance plan.

Additional Information

In addition to the two different forms on iron contained in Ferralet-90, it also contains:

  • Folic acid
  • Vitamin C
  • Vitamin B12
  • Docusate (stool softener)

Vitamin C is added to some products to enhance iron absorption. Studies indicate that vitamin C can increase absorption of 30 mg of elemental iron by about 10%.

The most common side effects of iron supplementation include:

  • Nausea
  • Vomiting
  • Diarrhea
  • Constipation
  • Dark stools
  • Changes in taste (liquid preparations)

Iron should be initially be taken on an empty stomach to maximize absorption. However, if you are having difficulty tolerating it, food may reduce gastrointestinal discomfort.

If food isn't helping you better tolerate iron, you can consider:

  • Trying a product with less elemental iron or slower absorption.
  • Taking smaller, less frequent doses.

Going back to the dizziness you are experiencing, it could be from the iron product you are taking (although the prescribing information for Ferralet-90 doesn't list it as a known side effect), but also may be due to other factors (such as low iron levels not properly being treated)

Your best bet is to discuss your therapy with your doctor so you can be evaluated and see whether or not your medication should be adjusted.

If the Ferralet-90 was too expensive, there are certainly other options, but they may have to be dosed in a different way from which you are currently taking it.

  1. Diagnosis and management of iron deficiency anemia in the 21st century. PubMed
  2. Carbonyl iron therapy for iron deficiency anemia. PubMed
  3. Comparison Study of Oral Iron Preparations Using a Human Intestinal Model. PubMed
  4. Iron-Deficiency Anemia. NEJM
  5. Oral Iron for Anemia: A Review of the Clinical Effectiveness, Cost-effectiveness and Guidelines. PubMed
  6. Comparative assessment of the bioavailability, efficacy and safety of a modified-release (MR) carbonyl iron tablet and oral conventional iron preparation in adult Indian patients with nutritional iron deficiency anaemia. PubMed
  7. High-dose carbonyl iron for iron deficiency anemia: a randomized double-blind trial. American Journal of Clinical Nutrition
  8. Bioavailability of carbonyl iron: a randomized, double-blind study. PubMed
  9. Clinical inquiries. Are any oral iron formulations better tolerated than ferrous sulfate. PubMed
  10. Diagnosis and management of iron deficiency anemia in the 21st century. American Journal of Clinical Nutrition