Ferrous Sulfate Vs. Ferrous Gluconate: What Is The Difference?

Thank you for reaching out to us! You're right that there are a variety of iron supplements available over the counter, and we're happy to help talk about the difference between the two you mentioned in your question.

Ferrous gluconate and ferrous sulfate are the two most commonly used iron supplements. They both have similar efficacy and tolerability when used at equal doses of elemental iron. You really can't go wrong with either one.

The primary thing to be aware of between these two iron products is that they differ in the percentage of elemental iron they contain. This is especially important if your doctor has instructed you to take a certain amount of iron per day.

You really want to look at the amount of elemental iron a product contains as the milligram amount of elemental iron contained in iron supplements is significantly less than the mg amount of the entire compound.

For example, the most common strength of ferrous sulfate is 325 mg per tablet. However, that 325 mg refers to the entire 'ferrous sulfate' compound. The actual amount of elemental iron is 65 mg (which should be signified on the label of the product). I talk about this more in the next section.

Comparison

Ferrous Gluconate

Ferrous gluconate is the second most commonly used over-the-counter iron supplement, behind ferrous sulfate. Ferrous gluconate contains 12% elemental iron by weight. Below, is the label for Mason Ferrous Gluconate tablets:

You can see on the label that this product contains ferrous gluconate 240 mg, yielding only 27 mg of elemental iron.

Ferrous Sulfate

Ferrous sulfate contains a higher percentage of elemental iron than ferrous gluconate. It contains approximately 20% elemental iron by weight. To illustrate this, below is a picture of the label for Mason Ferrous Sulfate:

This product contains ferrous sulfate 325 mg, yielding 65 mg of elemental iron (about 20% elemental iron by weight).

When comparing ferrous gluconate and ferrous sulfate supplements, it is important to look at the drug label and identify exactly how much elemental iron is contained in them. As an example, you would need to take 2.4 tablets of 240 mg ferrous gluconate to equal the amount of elemental iron (65 mg) contained in 1 tablet of ferrous sulfate.

Additional Information

In terms of dosing, you ideally want to take iron supplements on an empty stomach to maximize absorption as food greatly decreases the amount of iron our bodies absorb. However, iron can be very difficult to tolerate and commonly causes nausea, vomiting, and stomach cramps. If this happens, a little bit of food (e.g. crackers) can help.

Since ferrous gluconate contains less elemental iron, it tends to cause less gastrointestinal discomfort. If you cannot tolerate ferrous sulfate, one option is to dose ferrous gluconate two to three times daily (about 6 to 8 hours apart) to get to your supplemental iron dose.

Aside from the difference in the percentage of elemental iron, there are no significant differences between ferrous sulfate and gluconate. Most studies indicate similar effectiveness in raising iron levels and similar tolerability (when dosed in equal amounts of elemental iron).