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?...


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.

2 thoughts on “Is Long-Term L-Lysine Safe for Cats?”

  1. As a reply to if it’s okay to give cats Lysine for life.. I’m just wondering if it is capable of causing a deficiency of arginine and if so, what are dome signs and symptoms to watch out for? I myself give my cat Lysine daily and she just seems to sleep most the day and night. She’s only 1 year and 4 months young, so I find this odd. I try to play with her and keep her stimulated, but she’s just not fazed by much. She’ll play for a little bit and lay back down. She is FIV positive, so maybe that could be the cause of her excessive sleep? She also has days where she eats okay and other days that she won’t eat anything at all, but will still drink water. Lately, she has been been throwing up, just solid food, maybe once or twice a week. She’s a very slow eater and I only feed her the best foods, wet and dry, that are grain free and meat is 1st on the ingredient list. Blue Buffalo to be exact. Could the long term usage of Lysine be contributing to some of these symptoms. I myself take Lysine for anxiety and it makes me tired, lowers my blood pressure to where I get dizzy if I stand too quick, so could this be whats happening to my cat? Thank you for your time! Love your articles!

    1. Melissa W. It most definitely can cause a deficiency of arginine which cats need they could die without it they get very sick and can’t eliminate toxins and get ammonia toxicity I found this all out the day I started my cat on l lysine but what I got out of the research is it’s ok to give short term but not long term because of lowering arginine. My cat always has watery eyes and sneezing we got her off the street after 2 different vets and antibiotics and eye ointments she still had it she doesn’t have the feline diseases that cause it according to tests it must be allergies so I am trying l lysine treats for a week to 2 weeks to help her immune system hopefully then I plan on stopping.Hopefully the person who wrote this article sheds some insight on this.

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