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Is lysine for cat herpes safe, or is it harmful to their health?

Updated On September 23rd, 2025

Pet's info: Cat | Domestic Shorthair | Male | neutered | 4 years and 7 months old | 13 lbs

My cat was having sneezing fits due to the herpesvirus. My vet instructed me to give a 500mg lysine chew in the morning and a 500mg chew at night. I have been doing this since Monday and have noticed a significant improvement. However, I read online that it doesn’t work and is actually harmful to the cats. Is it true that its potentially detrimental to my cats health?

2 Answers

Most Helpful Answer

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Answered By Sara Farmer, DVM

Veterinarian

Published on August 22nd, 2018

Lysine supplementation for herpesvirus is controversial. The idea behind supplementation is that increasing lysine levels would decrease arginine (another amino acid) levels and since the herpesvirus needs a lot of arginine to replicate it would slow the virus down and improve clinical signs. Scientific studies have not shown any improvement in clinical signs when cats are supplemented with lysine. There was a review article published in 2015 that suggested that supplementing cats with lysine might be dangerous since it could lead to arginine deficiency in cats, but to my knowledge this has not been backed up by scientific evidence either. I personally don't recommend lysine because I have not had many success stories with it, however I also don't discourage people from using it.

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    Answered By Dr. Melanie, BVSc MS

    Veterinarian

    Published on

    Don't believe everything you read online! Things like that are often written by people who have no veterinary training at all, and don't know what they are talking about. There is no way your vet would have told you to give the lysine chew to Leo if it was detrimental to his health. It's fine to give to him. I hope this helps!

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