NOW - L-Lysine - 250 Capsule(s) - NPN: 80002648 -- L-Lysine is an essential amino acid that must be obtained through the diet or through supplementation.* Lysine is necessary for the production of all proteins in the body, and is required for the maintenance of the structural proteins collagen and elastin, which form all connective tissue such as skin, tendon, and bone.* L-Lysine is also a precursor to L-carnitine, which is needed for fat metabolism and energy production.* In addition, L-Lysine may help to support a healthy immune system and proper cardiovascular functionLysine is an amino acid (building block of protein). People use it to make medicine.Lysine is used for preventing and treating cold sores (caused by the virus called herpes simplex labialis). It is taken by mouth or applied directly to the skin for this use.Lysine is also taken by mouth to improve athletic performance.