L-lysine may treat and prevent cold sores, states Drugs.com. Although it is not a cure for the herpes simplex virus which causes cold sores, some studies suggest that taking L-lysine can prevent or reduce the duration and intensity of cold sores.
Cold sore development is dependent upon the amino acid L-arginine, states Drugs.com, and L-lysine may encourage the breakdown and reabsorption of L-arginine.
Because L-lysine is classified as an essential amino acid, it must be introduced through diet or through supplements as it is not created naturally in the body, states Everyday Health. L-lysine can be taken as a supplement.