Our L-Lysine formula is an essential amino acid that cannot be made by the body. Amino acids form the basis for protein, which helps construct and maintain the critical structures in the body.? Lysine can also help fight cold sores.? All Windmill supplements are manufactured in the United States in an FDA-inspected facility whose GMPs (Good Manufacturing Practices) are independently verified by qualified certification organizations. Free of artificial colors, flavors and preservatives, Windmill is a trusted name that has been providing America with quality supplements for over 40 years.