Alternate-Day vs. Once-Daily Oral Iron Supplementation in Iron Deficiency Anemia (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 * The participant requests to withdraw from the research study. * Hemoglobin level decreases by 1 g/dL or more compared to baseline at Week 4 or Week 8. * Blood hemoglobin level increases by less than 1 g/dL following the evaluation at Week 4 or Week 8, which is considered treatment failure. * Occurrence of severe complications, such as symptomatic anemia or circulatory collapse, requiring intravenous iron therapy or blood transfusion. * Occurrence of severe adverse events that render the participant unable to tolerate oral iron, even after dose reduction. Treatment Failure \- Increase in hemoglobin level of \< 1 g/dL at Week 4 or Week 8 compared with baseline.