Updated June 2022
It's tricky to iron out differences among oral iron supplements. Efficacy and tolerability are similar at equal doses of elemental iron. But the percent of elemental iron varies between products.
For the treatment of iron deficiency, expect most patients to need 100-200 mg/day elemental iron - exact needs will depend on several factors such as age, biological sex, pregnancy or breast-feeding status, and menopausal status. Suggest ferrous sulfate or fumarate. These typically have 65-100 mg of elemental iron per tablet, compared with only about 35 mg in a ferrous gluconate tablet.
Products containing more elemental iron tend to cause more GI upset and constipation. Suggest starting with just one tablet daily and titrating up to twice daily over a week or two as tolerated. Alternate-day dosing can also be considered as an option. Taking ferrous sulfate 60 mg on alternate days in single doses appears to improve iron absorption when compared with taking 60 mg once daily. But for patients with severe iron deficiency anemia, twice daily dosing may result in a faster response. Also explain that iron is best absorbed on an empty stomach, but it's okay to take it with food if GI upset occurs.
Vitamin C slightly increases iron absorption, but most combination products don't have enough vitamin C to make a difference. Don't feel compelled to recommend other forms of iron. Explain that slow-release or enteric-coated iron products may not be absorbed as well because they dissolve later in the GI tract. And point out that there's no proven advantage to using more costly forms, such as polysaccharide-iron complex (Ferrex 150, etc), carbonyl iron (ICAR), or heme iron polypeptide (Proferrin ES, etc).
Check our Commercial Products Database for details on specific iron supplements.
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