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Ferrous Sulfate Dosage: Guidelines for Adults and Children

Last reviewed: December 2025

Overview

Ferrous sulfate dosing depends on whether you’re treating iron deficiency anemia or preventing iron deficiency. The amount of elemental iron—not the total tablet weight—is what matters for dosing.

A standard 325 mg ferrous sulfate tablet contains approximately 65 mg of elemental iron. This distinction is important when comparing different iron supplements.

Standard Dosages

Adults (Treatment of Iron Deficiency Anemia)

Typical therapeutic dose:

  • 325 mg (65 mg elemental iron) 2-3 times daily
  • Total: 130-195 mg elemental iron per day
  • Take on empty stomach when tolerable

If GI side effects occur:

  • Start with 325 mg once daily
  • Gradually increase over 1-2 weeks
  • Take with food if needed (reduces absorption by ~40%)

Adults (Prevention)

General prevention:

  • 325 mg (65 mg elemental iron) once daily

Pregnancy:

  • 27-30 mg elemental iron daily (often in prenatal vitamins)
  • Higher doses if anemia is present

Children

Infants (treatment):

  • 3-6 mg/kg/day elemental iron in 2-3 divided doses
  • Use liquid formulation

Children 1-12 years (treatment):

  • 3-6 mg/kg/day elemental iron
  • Maximum: 195 mg elemental iron per day

Adolescents:

  • Adult dosing appropriate for most

Administration Guidelines

Optimal absorption:

  • Take on empty stomach (1 hour before or 2 hours after meals)
  • Take with vitamin C (orange juice, supplement) to enhance absorption
  • Avoid taking with milk, coffee, tea, or calcium supplements

Timing considerations:

  • Space doses evenly throughout the day
  • Take at least 2 hours apart from:
    • Antacids
    • Proton pump inhibitors
    • Tetracycline antibiotics
    • Quinolone antibiotics
    • Levothyroxine
    • Calcium supplements

Liquid formulations:

  • Use dropper or measuring device provided
  • Mix with water or juice to prevent tooth staining
  • Use a straw and rinse mouth afterward

Extended-Release Products

Products like Slow FE may be taken once daily:

  • 160 mg ferrous sulfate (50 mg elemental iron)
  • Take with water, with or without food
  • Do not crush or chew extended-release tablets

Special Populations

Pregnancy:

  • Follow prenatal vitamin recommendations
  • Additional supplementation only if diagnosed with deficiency
  • Iron needs increase throughout pregnancy

Elderly:

  • Standard adult dosing
  • May need lower doses due to increased sensitivity to side effects
  • Consider checking for underlying causes of deficiency

Kidney disease:

  • May need dose adjustment
  • Often use IV iron instead for dialysis patients
  • Consult nephrologist

Malabsorption conditions:

  • May need higher doses
  • Consider liquid form
  • IV iron may be necessary

Missed Dose

  • Take as soon as remembered
  • If close to next dose, skip the missed dose
  • Do not double doses
  • Continue regular schedule

Overdose Warning

Iron overdose is serious and potentially fatal, especially in children:

Symptoms of overdose:

  • Severe nausea and vomiting
  • Bloody diarrhea
  • Abdominal pain
  • Shock

If overdose suspected:

  • Call Poison Control immediately: 1-800-222-1222
  • Seek emergency medical care
  • Keep iron supplements in child-resistant containers

Sources

  • FDA-approved labeling for ferrous sulfate products
  • American Society of Hematology guidelines
  • National Institutes of Health Office of Dietary Supplements
  • Clinical pharmacology references
Last reviewed: December 2025