What Are the Uses of Lysine for Cats?

Dan Harkins

Many humans view the amino acid lysine as a useful supplement to strengthen the absorbency of supplemental calcium and to reduce the frequency of herpes simplex outbreaks. For cat owners, this protein component is also a respected treatment for quelling herpes outbreaks, though the symptoms are quite different for felines than humans. Lysine is also different for cats than for humans in that cats require a much smaller dosage. Widely sold by the brand name Viralys®, lysine is most often administered to cats as a pill or as a powder that can be camouflaged in a cat's food.

The structure of lysine.
The structure of lysine.

Feline herpes reveals itself as an respiratory infection for cats. Flu-like symptoms are most prevalent, including wheezing, cold sores, sneezing, fever and lethargy. Another prevalent symptom is a condition called conjunctivitis, which causes the eyes to swell and emit discharge. Though related to the human versions on the cellular level, this type of herpes cannot be transmitted to humans or other types of household pets.

Lysine may be available in pill form.
Lysine may be available in pill form.

Lysine for cats has a different dosage than for humans, too. Both mammals produce a certain amount that decline with age. According to the University of Maryland Medical Center, humans regularly take as much as 9,000 mg daily to end a herpes outbreak, though 1,000 mg a day is a customary daily supplement. Lysine for cats is recommended at a daily dosage of no more than 500 mg, with half that for kittens. Though the symptoms of the feline herpes will often recede with treatment within a week, various outbreaks should be expected throughout a cat's life, similar to the human versions.

According to one lysine distributor, lysine for cats often accompanies other treatments. To ease the discomfort of the conjunctivitis and to aid in healing, veterinarians often recommend an eye ointment containing an anti-bacterial agent, such as tetracycline. Several other drugs might be administered by injection to ease inflammation or reduce the recurrence of outbreaks.

Aside from the lysine for cats that come in powder or pill form, which require special tactics to make a cat swallow them, some pet owners also turn to other more homeopathic types of supplements to help relieve the strain of the respiratory congestion. According to the Holisticat Web site, several herbs like olive leaf, propolis and grapefruit seeds have long been used to relieve congestion in humans and their pets alike. The Web site also maintains that other supplements might be effective in controlling feline respiratory infections, from lactoferrin to the colostrum of cows.

Cats require a much smaller dosage of Lysine than humans.
Cats require a much smaller dosage of Lysine than humans.

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Hello - I own a pet supply store and have seen no improvement in symptoms for cats with herpes virus with Lysine supplementation, though immune support has shown us almost immediate improvement in symptoms such as respiratory and eye issues. So, I did some digging, and saw this fairly recent paper suggesting that Lysine is ineffective in cats for FHV-1 and in fact may be detrimental or even dangerous. Thought I'd pass it along in case your vets hadn't seen it yet. Can's post a web address in this site's comments, but the title is "Lysine supplementation is not effective for the prevention or treatment of feline herpesvirus 1 infection in cats: a systematic review" BMC Vet Res. 2015; 11: 284.

Published online 2015 Nov 16. doi: 10.1186/s12917-015-0594-3

In the abstract it says: "There is evidence at multiple levels that lysine supplementation is not effective for the prevention or treatment of feline herpesvirus 1 infection in cats. Lysine does not have any antiviral properties, but is believed to act by lowering arginine levels. However, lysine does not antagonize arginine in cats, and evidence that low intracellular arginine concentrations would inhibit viral replication is lacking. Furthermore, lowering arginine levels is highly undesirable since cats cannot synthesize this amino acid themselves. Arginine deficiency will result in hyperammonemia, which may be fatal. In vitro studies with feline herpesvirus 1 showed that lysine has no effect on the replication kinetics of the virus. Finally, and most importantly, several clinical studies with cats have shown that lysine is not effective for the prevention or the treatment of feline herpesvirus 1 infection, and some even reported increased infection frequency and disease severity in cats receiving lysine supplementation."


@ysmina-- At the shelter I volunteer at, we give all the cats lysine supplements in their food. It will definitely help a malnourished cat improve her immune system. It's also very helpful for cats that get allergies and upper respiratory infections.

We have lysine in bulk, powder for and we just add some to their food and mix it up. You can definitely get the lysine made for humans, just make sure to lower the dose a bit. I think 500mg a day is a good dose during infections. You should confirm this with your vet though.


@ankara-- Did you give your cat regular l-lysine capsules made for human use? Or are there ones made for feline?

I just adopted a malnourished kitten from the shelter. She has been getting sick often, do you think l-lysine will help?


My cat had non-stop watering eyes for two weeks. The vet had given an antibiotic eye drop which helped a little bit, but the problem did not resolve. So I took her back and this time the vet told me about feline herpes and suggested lysine supplements.

I had heard about lysine supplements for cold sores, but I had no idea that cats can have herpes and that lysine is also good for them.

I gave my cat lysine supplements every day and I also continued with the eye drops. In a week, her eyes stopped watering. Lysine is a very good treatment for feline herpes.

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