L-Lysine is widely used in animal feed to balance amino acid composition, especially in poultry and swine diets, promoting optimal growth and protein synthesis. It is added to vegetarian and protein-deficient diets to ensure adequate essential amino acid intake. In pharmaceuticals, L-Lysine is used in nutritional supplements and intravenous feeding solutions to support tissue repair and immune function. It has also been studied for its role in managing herpes simplex virus infections, as it may help reduce the frequency and severity of outbreaks by interfering with arginine metabolism, which the virus needs to replicate. Additionally, L-Lysine serves as a building block in the production of antibiotics, such as cephalosporins, and is used in some biodegradable polymers for medical and industrial applications.

Furthermore, studies suggest that L-Lysine may aid in calcium absorption and contribute to bone health, particularly in older adults at risk of osteoporosis.