Lysine is an essential amino acid. Like all amino acids it functions as a building block for proteins. Proteins are essential for the formation of cells and are also involved in the biochemical structure of hormones, enzymes, neurotransmitters and antibodies.

Lysine is abundant in animal based foodstuffs such as red meat but found in much lower quantities in most vegetables. Hence, low dietary intakes are frequently seen in vegetarians.

Studies suggest that lysine may be helpful in controlling herpes simplex-related infections, which is the virus that causes cold sores.