If your cat has been diagnosed with feline herpes virus (FHV), you’ve probably heard of L-lysine as a go-to supplement. For years, it was commonly recommended by vets and pet professionals alike, often handed out as a fix for nearly any upper respiratory issue.
I’ll be honest, when I started working professionally with cats many years ago, I used L-lysine too. It was just what we did. But after diving deep into the research, listening to emerging evidence, and seeing real-world results in cats I have worked with, I’ve completely changed my stance.
Here’s why:
The Research on Lysine Is Conflicting
There have been studies done on L-lysine’s effects on feline herpes virus but the results are inconclusive. Some show mild benefits and others show zero effect at all. That alone is enough to raise eyebrows, but that’s not the only concern.
The Hidden Dangers of Lysine
One of the biggest risks of L-lysine is that it can interfere with another critical amino acid in your cat’s body: arginine.
And that’s a big deal.
Arginine is essential for healthy heart function, and for Sphynx cats who are already genetically predisposed to heart issues like HCM, this imbalance can become dangerous.
L-lysine in high doses has also been shown to cause issues in:
Pregnant cats and kittens
Cats with liver or kidney disease
What To Do Instead
First, always confirm a diagnosis. If your cat is showing symptoms of upper respiratory illness, ask your vet to run a Feline Upper Respiratory PCR Panel. This will identify whether you’re dealing with feline herpes virus, or any number of other viruses with similar symptoms, or even a bacterial infection. These would all need to be treated differently depending on the actual source of infection.
And if your cat does test positive for feline herpes virus?
Don’t reach for L-lysine.
Instead, send contact me at info@renewedpet.com and I will share the supplement I DO recommend - one that’s all-natural, safe, and actually supports the immune system in a way that helps cats heal from FHV.
