Is Long-Term L-Lysine Safe for Cats?

Just wondering if it is safe for a cat to be on L-lysine for a long time or perhaps for the rest of her life?...

Dr. Eric Barchas  |  Nov 17th 2008

Just wondering if it is safe for a cat to be on
L-lysine for a long time or perhaps for the rest
of her life? I have tried to take her off it and
her runny eye and sneezing seems to come back, so
she really needs to be on this. I would rather
this than antibiotics that she has tried without

Thank you.

Tina B
Vancouver Island, BC, Canada

L-lysine is a naturally occurring amino acid. It inhibits the replication of herpes virus.

In cats, herpes virus is not sexually transmitted. It is a highly contagious and extremely common cause of upper respiratory infections, or URIs. URIs are marked by eye discharge, squinting, sneezing, and and sinus congestion.

Almost every cat on earth is infected with feline herpes virus. Infection is lifelong. Feline herpes virus does not spread to people.

Most cats are able to suppress herpes virus with their immune systems. However, some cats suffer chronic or recurrent URIs as a consequence of infection with herpes virus. These cats may benefit from dietary supplementation with L-lysine.

L-lysine is a natural part of proteins. Adverse effects from long-term administration of L-lysine are extremely unlikely. If you feel that your cat is benefiting from the amino acid, I see nothing wrong with giving it for long periods. It is certainly safer than long-term antibiotics. And, since antibiotics do not treat herpes virus, L-lysine may also be more effective.

My 14-year-old cat has been sneezing and sounding
nasally congested. His eyes are bright, appetite
good, coat good, etc. is there anything OTC I can
give him for this?

Gainesville, Florida

Your cat sounds like he has a URI. Although many different viruses and bacteria can cause URIs, feline herpes virus is one of the most common culprits. L-lysine may help your cat. It is available over the counter (OTC). The recommended dose depends on the size of the cat, so talk to your vet about using L-lysine for this problem.

If L-lysine doesn’t help your cat, you should work with your vet to look for other possible causes of sneezing and congestion such as bacterial sinus infections or foreign objects such as blades of grass in the sinuses.