Lysine is an amino acid found in many proteins. Some people believe that lysine supplements may help fight viral infections, such as the infection that causes cold sores. Studies have not proved one way or the other if this is helpful. But some researchers suggest taking lysine supplements and avoiding foods such as nuts, chocolate, and gelatin (foods rich in the amino acid arginine) to treat cold sores.¹

People with kidney or liver disease should not take lysine.

Most cold sores will heal on their own without prescription medications or complementary therapies.