Hydroxyurea is a drug that can induce fetal hemoglobin expression, which inhibits the polymerization of sickle hemoglobin and reduces the pathophysiological effects of sickle cell disease. It works by acting as a DNA methyltransferase inhibitor and affecting globin gene regulation through microRNAs to reactivate fetal hemoglobin expression, which is an important therapeutic strategy for patients with hemoglobin disorders like sickle cell disease.