URI & L-Lysine in Cats

Watch out! I have an upper respiratory infection and feel a sneeze coming on.
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Upper respiratory infections aren't uncommon in felines. If your kitty gets sick, you want him well as soon as possible. Will supplementing him with lysine help clear up his URI? Probably not. At least, that's the conclusion reached in controlled studies on the subject. Your results may vary.


The essential amino acid L-lysine, or just plain lysine, isn't produced in the body, but must be obtained from food or supplements. According to the University of Maryland Medical Center, studies in humans have found that lysine prevents cold sore and genital herpes outbreaks. Protein-rich foods containing lysine, including fish, chicken and meat products, are often used in cat food.

Upper Respiratory Infections

It's not hard to recognize URI symptoms. Your kitty starts sneezing, his eyes run, mucus comes out of his nose ... it's pretty much the same thing that happens if you get a URI. Caused by viruses, cats suffering from URIs might also develop mouth ulcers and a discharge severe enough to gunk up his eyes and close them. Cats can develop fevers and secondary bacterial infections. Basically, your kitty feels like those deposits in his litterbox. Your vet might prescribe antibiotics to treat the bacterial infection -- they don't help viral infections. If your cat is dehydrated because he won't eat or drink, the vet might administer an IV solution to perk him up.

Risk Factors

Although URIs are very contagious, your cat probably won't pick one up unless he's around another cat suffering from one. However, if you adopt a cat from a shelter, find a stray or take home a cat from an overcrowded feline living situation, URIs are a possibility. Kittens are especially vulnerable, because of their immature immune systems. While the normal URI runs its course in less than two weeks, the viruses involved with it -- FHV-1 or the calici virus -- stay with the cat for life. They may or may not ever bother him again, or he could become symptomatic in times of stress.


According to a study conducted by researchers at the University of California at Davis Veterinary Medical School and published in 2009, supplementing with lysine did not successfully control infectious URI in group of 261 cats in an animal shelter. In fact, the study concluded that,"It led to increases in disease severity and the incidence of detection of feline herpes virus (FHV-1) DNA in oropharyngeal or conjunctival mucosal swab specimens at certain time points." That means the researchers swabbed the cats' mouths or under their eyelids for specimens. In non-scientific language, the cats given lysine supplements actually had worse cases of URI than the cats that weren't supplemented.The title of another study, published in 2008, says it all: "Oral supplementation with L-lysine did not prevent upper respiratory infection in a shelter population of cats."

Mouth Ulcers

While lysine might not help kitty recover from a URI, there is evidence that it aids in healing mouth ulcers caused by FHV or the calici virus. Special veterinary versions of lysine are available for cats. Rather than trying to give a cat a pill, these come in paste form. You can pump out a specific dosage and wipe it on your cat's paw for him to lick off, or mix it in his food if he'll eat it. Many vets do recommend lysine for their feline patients suffering from URIs. Studies done in shelters do reflect a feline population far more stressed than your beloved kitty. Whether it helps or not, it's unlikely to hurt him.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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