Maximum Daily Dose of Ferrous Sulfate
The maximum recommended daily dose of oral ferrous sulfate for adults is 200 mg of elemental iron per day, though most contemporary guidelines converge on 100 mg elemental iron daily as the optimal balance of efficacy and safety. 1
Standard Dosing Recommendations
For routine treatment of iron-deficiency anemia, 50–100 mg elemental iron once daily is the evidence-based standard, which translates to one 200 mg ferrous sulfate tablet (containing 65 mg elemental iron) taken once daily. 2, 1
Prescribing more than 100 mg elemental iron per day provides no additional benefit and may increase the risk of adverse effects, especially in patients with inflammatory conditions. 1
The upper limit cited across multiple guidelines is 100–200 mg elemental iron per day, with 200 mg representing the absolute maximum rather than a routine target. 1
Physiological Rationale for Dose Limits
Oral iron doses ≥60 mg trigger an acute rise in hepcidin that persists for approximately 24 hours, reducing the fractional absorption of any subsequent iron dose by 35–45%. 2, 1, 3
This hepcidin-mediated blockade creates a physiological ceiling that makes higher daily doses counterproductive—taking multiple doses per day increases side effects without improving absorption. 2, 1
Unabsorbed iron remaining in the gastrointestinal tract produces dose-dependent side effects such as nausea, constipation, diarrhea, and abdominal discomfort. 1
Practical Dosing in Ferrous Sulfate Tablets
A standard ferrous sulfate 200 mg tablet contains 65 mg elemental iron. 2, 3
To achieve 100 mg elemental iron daily, patients would take two 200 mg ferrous sulfate tablets once daily (providing 130 mg elemental iron). 1
To reach the 200 mg elemental iron maximum, patients would need three 200 mg ferrous sulfate tablets once daily (providing 195 mg elemental iron). 1
Special Population Considerations
Severe Iron-Deficiency Anemia
In patients with severe anemia (hemoglobin ≈7 g/dL) and depleted iron stores (ferritin ≈19 ng/mL), the higher end of the dosing range (≈200 mg elemental iron daily) is recommended to achieve rapid repletion. 1
This translates to three ferrous sulfate 325 mg tablets once daily (providing roughly 195 mg elemental iron). 1
Chronic Kidney Disease
In non-dialysis CKD patients, a minimum of 200 mg elemental iron daily is recommended, typically administered in two to three divided doses. 1
This represents an exception to the once-daily dosing rule and reflects the unique iron metabolism challenges in CKD. 1
Inflammatory Bowel Disease
Patients with IBD should receive no more than 100 mg elemental iron per day, and only when the disease is clinically inactive. 1
During active intestinal inflammation, oral iron absorption is markedly impaired and may exacerbate disease activity; intravenous iron is recommended as first-line therapy. 1
Safety Thresholds and When to Stop
Iron supplementation should be withheld when transferrin saturation exceeds 50% or serum ferritin exceeds 800 µg/L, as further supplementation offers no therapeutic benefit and raises the risk of iron overload. 1
Oral iron therapy should be discontinued when ferritin levels are normal or elevated, because continued supplementation may be harmful. 1
Common Pitfalls to Avoid
Do not prescribe ferrous sulfate 200 mg three times daily (the outdated traditional regimen)—this provides 195 mg elemental iron but increases gastrointestinal side effects by 2.32-fold compared to placebo without improving absorption. 2, 4, 5
Do not assume that higher doses will produce faster hemoglobin recovery—once-daily dosing of 50–100 mg elemental iron produces similar overall absorption to divided higher doses due to hepcidin elevation. 2, 1
If daily dosing causes intolerable side effects, switch to alternate-day dosing (every other day) with 100–200 mg elemental iron, which markedly improves fractional absorption and reduces gastrointestinal symptoms while maintaining efficacy. 2, 1, 3