Felisyl is a soft chew supplement that contains the amino acid L-Lysine for use in cats and kittens for conditions responsive to L-Lysine. L-Lysine is an essential amino acid, which means that your pet's body needs it, but can't produce it, so this supplement is a perfect choice to provide that necessity. L-Lysine HCL Immune System Support for Cats helps keep your cat healthy by supporting the immune system naturally so that it can function normally and produce antibodies. Felisyl L-Lysine HCL Immune System Support Soft Chews for Cats also helps maintain healthy tissue, supports respiratory health, and may even help with your cat's vision. The L-Lysine is in a chicken liver flavored soft chew making it easy to give to your cat.