Hi Virgina,

Viralys (and its counterpart Enisyl paste) are lysine supplements often used in cats that have recurring upper respiratory infections that typically are thought to have an underlying viral condition.  As it is an amino acid and to some extent natural, there are essentially no side effects, interactions, or monitoring involved.  It is best used as a long-term supplement plus many cats I know enjoy it as a treat!

All the best.

Dr. Ryan Llera