From the FDA Drug Label
Each tablet contains 324 mg of ferrous gluconate, equivalent to 38 mg of elemental iron, providing 211% of the U.S. recommended daily intake (RDI) of iron for adults and children 4 and older. Suggested Use For Adults, take one (1) tablet daily or as directed by physician
The most absorbable form of iron with the lowest GI side effects is not directly stated in the provided drug labels. However, ferrous gluconate and ferrous fumarate are both commonly used iron supplements.
- Ferrous gluconate 1 is equivalent to 38 mg of elemental iron per tablet.
- Ferrous fumarate 2 does not specify the amount of elemental iron per tablet in the provided text. To minimize GI side effects, it is generally recommended to start with a low dose and gradually increase as needed and tolerated. However, the provided drug labels do not provide a direct comparison of the GI side effects of these two supplements.
From the Research
Ferrous bisglycinate 25 mg iron is the most recommended iron supplementation for patients with minimal gastrointestinal side effects, as it has the most favorable GI side effect profile compared to ferrous fumarate and ferrous sulphate. This is based on a recent study published in the Journal of Pregnancy in 2024, which compared the frequency of GI complaints during low-dose oral iron prophylaxis with three iron formulas: ferrous fumarate, ferrous bisglycinate, and ferrous sulphate 3. The study found that ferrous bisglycinate 25 mg iron had significantly fewer GI complaints than ferrous fumarate 40 mg iron and ferrous sulphate 50 mg iron.
Some key points to consider when prescribing iron supplementation include:
- Starting with a lower dose and gradually increasing it can help minimize side effects
- Taking the supplement with food can further reduce stomach upset, though this may decrease absorption by 40-50%
- For optimal absorption, iron should be taken on an empty stomach with vitamin C (such as orange juice) to enhance uptake
- Treatment should continue for 3-6 months after hemoglobin normalizes to replenish iron stores
- Alternate-day dosing of oral iron supplements may be preferable as it can increase fractional iron absorption (FIA) by 40-50% compared to consecutive-day dosing, as shown in a study published in Haematologica in 2020 4.
It's also worth noting that other studies have compared the effects of different iron formulations and dosing schedules, but the study by 3 provides the most recent and highest-quality evidence for the recommendation of ferrous bisglycinate 25 mg iron for patients with minimal gastrointestinal side effects.