Lets talk about L-lysine.
There is a world of misinformation out there on this tricky little Amino Acid and often times it’s recommended by pet owners. I’ve heard people make claims it boosts the immune system, it’s an antiviral, it cures herpes or other upper respiratory infections etc. Unfortunately, pet owners are not alone as many vets aren’t up to date on the newest information we have regarding L-lysine and cats, so these pet owners are at a disadvantage, simply trusting their vets. The medical field of veterinary science is forever evolving and changing as we learn and discover more, so it is paramount for Veterinarians to continue their education.
So, what is it? What does it do? And why do people think it helps for Herpes?
As I said above, it’s an amino acid. Not an antiviral, not an antibiotic, not an immune system booster. It is simply not capable of working under any of those assumptions and does not function under those capacities in the slightest. It is thought to antagonize arginine in the cats system, and Herpes uses arginine to replicate, so it was anecdotally presumed that administering something that lowers the levels of arginine in the body would in term reduce the replication of the Herpes virus. Unfortunately this doesn’t work, and lowering arginine levels in a cat is highly undesirable as it’s essential for proper immune function and arginine deficiency can lead to fatal hyperammonemia.
A review of 17 studies in 2015 concluded that not only does L-lysine have zero benefit in the way of reducing Herpes replication or flare ups, but it in fact increased the severity of symptoms in some cats.
Dr.Addie, one of the leading experts in the world on FIP, vehemently recommends against its use in cats due to the negative effect it has on the immune system.
The newest edition of the Merck Vet Manual no longer recommends its use in cats for treating upper respiratory infections as well. It reads as follows;
“Previously, lifelong oral L-lysine (250-500 mg/day) was recommended to help prevent or reduce the severity of recurrent feline herpesvirus infections. However, recent work has shown that oral L-lysine can actually exacerbate feline herpesvirus infections.”
Stop recommending L-lysine. If your vet suggests it to you, question which recent study verified it to be beneficial, inquire about the excerpt from the Merck Manual, you are your pets best advocate so speak up for them, don’t be shy.