SCD is an inherited blood disorder. Symptoms include anemia, infections, organ damage, and intense episodes of pain that are called "sickle cell crises." SCD is caused by an abnormal type of hemoglobin, which is a protein inside red blood cells that carries oxygen. In people with SCD, the abnormal hemoglobin distorts the shape of the red blood cells. This causes the red blood cells to clump together, decreasing blood flow and oxygen delivery to the body's tissues. The reduced levels of oxygen can lead to sickle cell crises and tissue damage. Hemolysis, the destruction of red blood cells, is also a hallmark of SCD. During hemolysis, hemoglobin is released into the bloodstream, where it removes nitric oxide (NO), a natural chemical in the body that expands blood vessels. Arginase, another protein released during hemolysis, removes arginine from the bloodstream, which can also lead to decreased NO levels. The lack of NO constricts blood vessels, further contributing to painful sickle cell crises. Arginine supplementation may increase healthy hemoglobin and NO production and, in turn, prevent or reduce sickle cell crises. The purpose of this study is to evaluate the effectiveness of arginine at increasing NO levels, improving red blood cell function, and reducing hospitalizations and pain medication use in people with SCD.