The goal of this clinical trial is to compare the effectiveness and tolerability of two different oral iron regimens in adults with iron deficiency anemia (IDA). The main questions it aims to answer are:

Is alternate-day oral iron supplementation as effective as once-daily dosing in improving hemoglobin levels?

What are the side effects associated with each dosing regimen?

Researchers will compare once-daily vs. alternate-day oral ferrous fumarate to evaluate whether alternate-day dosing is non-inferior in terms of hematologic response, with fewer adverse effects.

Participants will:

Be randomly assigned to take ferrous fumarate 200 mg once daily or 400 mg on alternate days for 8 weeks

Undergo blood tests and clinical assessments at baseline, Week 4, and Week 8

Report any side effects and bring remaining pills to evaluate medication adherence

This is a multicenter, randomized, open-label, non-inferiority trial conducted in adults aged 20 years or older with IDA.

Inclusion Criteria:

• Male or female patients aged ≥20 years diagnosed with iron deficiency anemia, defined as: hemoglobin (Hb) <13 g/dL in males or <12 g/dL in females, and ferritin <50 ng/mL or transferrin saturation (TSAT) <20%.
• No iron supplementation within the past 3 months.

Exclusion Criteria:

• Hemodynamic instability (e.g., acute bleeding or hypotension).
• Severe heart failure (New York Heart Association [NYHA] Class III-IV) or other active cardiac diseases.
• Active malignancy or history of cancer within the past 3 years (except non-melanoma skin cancer).
• Pregnancy or breastfeeding.
• Chronic liver disease including cirrhosis (Child-Pugh class B or C).
• Chronic kidney disease (estimated glomerular filtration rate [eGFR] <60 mL/min/1.73 m²).
• Clinically significant thalassemia or hemoglobinopathies.
• Ongoing infection or chronic inflammatory diseases (e.g., rheumatoid arthritis, inflammatory bowel disease).
• Malabsorption disorders (e.g., history of bariatric surgery).
• Red blood cell transfusion within the past 3 months.

Withdrawal Criteria

• Withdrawal of informed consent.
• Severe adverse events requiring permanent discontinuation of study medication.
• Investigator's judgment that continued participation poses a safety risk.
• Non-adherence to study medication (compliance < 75%).

Treatment Failure

- Increase in hemoglobin level of < 1 g/dL at Week 4 or Week 8 compared with baseline.

Individual participant data (IPD) will not be shared due to institutional policy and privacy concerns. Only aggregate data may be shared upon reasonable request.