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.