l-Arginine supports nitric oxide formation, important for healthy dilation of blood vessels, circulation, and blood flow. In trials, l-arginine has demonstrated the potential to support endothelial function in blood vessels, platelet function, exercise tolerance, and sexual function. Because of its effect on nitric oxide production, l-arginine is theoretically best avoided by individuals with migraines, depression, autoimmune disorders, and kidney or liver disease. l-Arginine is contraindicated for individuals with the herpes virus.