Study Finds L-Lysine Does Not Decrease Symptoms of Feline Upper Respiratory Infections


Upper respiratory infections are common in cats, and the symptoms of these kitty colds – sneezing, runny nose, runny eyes, lack of appetite, fever – are very much the same as what we experience during a cold. In addition to conventional treatments such as antibiotics or antiviral drugs, L-Lysine supplementation is often recommended to treat symptoms and prevent a recurrence. According to a recent study, more than 90 % of veterinarians in cat hospitals recommend L-Lysine supplementation.

What causes upper respiratory infections?

Upper respiratory infections are caused by either a viral or bacterial infection. The two most common viruses that cause upper respiratory infections in cats are herpes and calici. Bacterial infections are most commonly caused by mycoplasma pneumoniae, bordatella bronchiseptica, and chlamydia psittaci bacteria.

Study finds L-Lysine supplementation is ineffective and potentially harmful

A recent study looked at infections caused by herpes virus 1, and found that L-Lysine supplementation was not effective in preventing or treating herpes infections in cats. L-Lysine supplementation also didn’t decrease the development of clinical signs, nor did it aid in treating symptoms.

L-Lysine does not have antiviral properties, but researchers found that it does lower arginine levels. Arginine is an essential amino acid that is involved in a number of different functions, including wound healing, helping the kidneys filter waste products, and maintaining immune and hormone function. Cats cannot synthesize this amino acid themselves, and arginine deficiency can result in hyperammonemia (a metabolic disturbance characterized by an excess of ammonia in the blood,) which can be fatal.

Finally, and most importantly, several clinical studies with cats have shown that L-lysine is not only not effective for the prevention or the treatment of feline herpesvirus 1 infection, some even reported increased infection frequency and disease severity in cats receiving L-Lysine supplementation.

Should you stop L-Lysine supplementation?

The study’s conclusion recommends an immediate stop of L-Lysine supplementation because of the complete lack of any scientific evidence for its efficacy. Fern Crist, DVM, a former board member of the American Association of Feline Practitioners, says she can’t count the number of cats she’s put on L-Lysine over the more than 30 years she’s been practicing, but says that, based on these findings, “I’m inclined to stop using L-Lysine, at least for the time being, and wait for more information.” Dr. Andrea Tasi, a feline veterinarian and owner of Just Cats Naturally, doesn’t recommend L-Lysine anymore. “Over time I came to see it didn’t do much for most cats,” she says.

You can read the full text of the study here.

32 Comments on Study Finds L-Lysine Does Not Decrease Symptoms of Feline Upper Respiratory Infections

  1. Virginia Dominguez
    March 12, 2017 at 10:42 am (2 months ago)

    My cat developed a serious eye infection in one of his eyes and was prescribed a lengthy course of antibiotics. The infection would reoccur with discharge s well. I started him on l lysine 2x day for possibly 6 Mos.. I am happy to say that he has recovered completely and is symptom free since then. I know that l lysine does work.

  2. Kip
    February 28, 2017 at 11:51 pm (2 months ago)

    My pound Cat has been on L-Lysine since she was a kitten and diagnosed with Feline Herpes, at that time both her normal Vet and her Specialty Vet had advised us to use it. As long as she is on it her eyes are bright and clear when we forget to order more and run out her eyes start getting goopy. After reading some of these reply’s I will keep my cat on L-Lysine because I personally see the positive results.

  3. Sayyad
    January 25, 2017 at 6:22 pm (3 months ago)

    They said stop using Lysine OK but what else to use
    Is there an over the counter thing that works

  4. Lynnette
    January 16, 2017 at 6:23 pm (3 months ago)

    I’ve been using L Lysine (gel & treats) for 18 months on my rescue with herpes. His sneezing (prev 20-30 at a time) has almost stopped completely and he no longer sleeps the entire day away. If I miss a dose or two, here come those sneezes! His infections are much more controllable now.

    • Beverly
      January 17, 2017 at 12:10 pm (3 months ago)

      I have two cat rescues that I use L-lysine for. Paste from the vet and chews from Global Pets and or Pet Value. Symptoms are under control while using the lysine. However, if I happen to run out or miss some doses, symptoms come back. One is worse than the other. I would really worry if I did not have this to give to them. I feed high quality wet food, and try to keep everything natural. My home is very green.

    • Barbara
      January 21, 2017 at 9:38 am (3 months ago)

      I’m glad to hear this, because my cat was sneezing so much he had nose bleeds and taking L-Lysine stopped these symptoms and I have recommended it to others.

      • Sayyad
        January 25, 2017 at 6:23 pm (3 months ago)

        So you mean Lysine workes

  5. Jan
    January 16, 2017 at 1:27 pm (3 months ago)

    Instead of L-Lysine, can Nettle-Eyebright or Lung Gold be used for the same treatment?

    • Ingrid
      January 16, 2017 at 2:53 pm (3 months ago)

      I’m not familiar with those products, Jan.

    • Sayyad
      January 25, 2017 at 6:24 pm (3 months ago)

      Is that usable also

  6. Anya
    December 12, 2016 at 8:14 pm (5 months ago)

    Thanks for sharing, a decrease in arginine is detrimental to a cat’s health. My vet also told me that he no longer suggests people use this for their kitties, as it’s not effective and may cause kidney distress.

    As for the folks ripping into scientists, most are very good people that are using the scientific method to back-up the claims that so many have been making without conclusive evidence. There are reviewers that scrutinize every word and method, so being one myself, I know the rigor these people go through, no need to bash them.

    Lysine does not work the same way in humans and lysine actually does help with HSVI in humans, but being that it depletes arginine in cats and causes kidney distress, there’s no way my guys will get it ever again.

  7. Bob Chapel
    June 7, 2016 at 11:42 pm (11 months ago)

    It is disquieting to me that so many ” researchers” are turning to retrospective studies ( I suspect as an easier way to meet their professional publishing requirements) which often do little to enlighten…seldom add anything to the body of knowledge and, in general, cause a lot of consternation among people who were happily using products that they felt WERE helping for years. I would SO prefer that more time and effort were put into NEW studies of these ( purportedly) time tested disease aids to examine ANEW if the claims are born out…. One always has to wonder if the individuals who did these retrospectives were judicious in their choice of articles or had a ” bone to pick” themselves….. I have nothing positive or negative to say about L-Lysine… I use it currently with my 3 FeLV+ youngsters as part of a VERY comprehensive regime of supplements…. Hard to say if it is working because I would only know if I stopped….waited for symptoms and then started again…… Many of us use supplements simply to feel some sense of control….as though we are DOING something….hoping that MAYBE it will do some good… It would be, of course, nice to have more definitive information

    • Anya
      December 12, 2016 at 8:17 pm (5 months ago)

      Taking science seriously when researchers use sound methods to show that something doesn’t work doesn’t mean they are attacking you personally or your vet. They simply said what they found and how they found it. Arginine depletion is rough on cats and when “researchers” try to enlighten others, I promise they do it because they are concerned with folks using an amino acid as a cure all when it is doing more harm than good.
      Many vets are now advising clients to back off of lysine, as renal failure is a bit more devastating than sneezing.

  8. Kara
    March 22, 2016 at 12:27 pm (1 year ago)

    I have a cat with herpes and for years I’ve kept it under control with
    VETOQUINOL Enisyl-F Lysine Treats but they’ve changed the formula and he won’t touch it now. Apparently LOTS of other people are complaining about the same thing. I don’t see my vet til next week for annual exam and bloodwork. What can someone recommend in place of this? He loved the old formula. If I use powder, I’m afraid the other cats will get some and my DVM says NO other cats should have the Lysine. Thanks in advance for anyone’s recommendations.

    • Nancy
      March 24, 2016 at 4:21 am (1 year ago)

      I put the powder in a can of wet food, and feed the cat that needs it in another room.

  9. Nelda
    January 18, 2016 at 1:59 pm (1 year ago)

    I have read this study and it DOES NOT prove that lysine is ineffective or harmful for cats. You have an obligation to your readers to get a professional to evaluate this study. And it needs to be someone who knows how to interpret this specific type of study. One of the main problems with this study is that it was a retrospective analysis of multiple previously published research studies. This type of study can never PROVE anything. Secondly, the authors included old studies of lysine use in humans, dogs, and laboratory test tubes. Really?!?!? By doing this, the authors have violated one of the main rules for conducting these types of studies that look back at what other researchers have previously published. In fact, this study was so poorly conducted that no conclusions can be drawn from it at all, let alone making recommendations about how to treat our kitties.

    • Roki
      June 25, 2016 at 9:40 am (10 months ago)

      Hear, hear. Not convinced by “reviews” of results of old, poorly conducted tests. One thing that did stick out was that *maybe* it’s not so good for kittens (presumably since their immune system isn’t fully developed?). Also, stress levels seemed to have a negative impact on all levels & increased the clinical signs. But we knew that, didn’t we…

  10. Jennifer
    January 18, 2016 at 12:45 pm (1 year ago)

    I have an 11 year old cat with feline herpes. My old vet recommended l-lysine and I had him on it per her instructions. We moved and my new vet actually recommends Forti-Flora which is a feline probiotic. I also have a tube of Teramycin for his eyes when he has a flare up. Both products can be purchased online. (My vet had prescribed the Teramycin for him previously).

  11. Beverly Oziel
    January 11, 2016 at 8:09 pm (1 year ago)

    I have two cat rescues that I give l-lysine treats to daily, it keeps both of there symptoms under control. If I forget to buy the treats and they miss out, there symptoms come back. Now I’m concerned about the side effects.

    • Ingrid
      January 12, 2016 at 5:41 am (1 year ago)

      I would discuss your concerns with your vet, Beverly.

  12. Maureen
    January 11, 2016 at 7:41 pm (1 year ago)

    This study can say whatever it wants. I have a cat with Feline Herpes, every day I put 1/4 teaspoon Now brand Lysine in his breakfast and again at dinner. When I forget ( I rarely have) his eye gets blinky and the sneezing begins. I also had a cat who came to me FIV positive, he also had Herpes and his eye ran constantly he was chronically congested. That darn Lysine made a huge difference.

  13. Maria Gambel
    January 11, 2016 at 7:23 pm (1 year ago)

    Could you please give a link to the study? Thank you.

    • Ingrid
      January 12, 2016 at 5:44 am (1 year ago)

      The link is in the last line of the article, Maria.

  14. Heather - CatMom to Lord BearCat
    January 11, 2016 at 8:29 am (1 year ago)

    Per my vet’s direction, I give my cat L-Lysine twice daily since he has FIV (but shows no symptoms). I guess I need to research this a bit more. Thanks!

  15. Janine
    January 11, 2016 at 7:38 am (1 year ago)

    I’ve heard a lot of people who claimed to have success using L-Lysine. Even my vet recommended it for one of my cats who is always sick with respiratory infections. But he refused to have anything to do with it, so I stopped trying to give it to him.

  16. Sue Brandes
    January 11, 2016 at 7:21 am (1 year ago)

    I use the L-lysine treats for my cat that has Herpes and it has helped him not have any outbreaks. Was using the paste for my cat that is prone to colds and it never did anything for him.

  17. Nancy
    January 11, 2016 at 4:31 am (1 year ago)

    Oh, great, I have a large container of it, I’ve been giving it to 2 foster cats who have reoccurring colds (they have already been on antibiotics). I see the study was about the herpes virus, but what about lessening the length of colds (like taking vitamin C or Cold ease for humans?

    • Ingrid
      January 11, 2016 at 5:43 am (1 year ago)

      I’m not aware of any studies that L-Lysine reduces the length of colds in cats, and given the evidence that it actually increased severity and frequency of disease in some cats, I would not expect it to do any good.

      • Nadine
        January 11, 2016 at 10:45 pm (1 year ago)

        My cat was prescribed Tobramycin Ophthalmic solution eye drops and L-Lysine chews for a runny discharge from both eyes. She is better since the treatment. Was the Lysine not necessary? I will share this with my vet. Thank you!!!

        • Nancy
          January 12, 2016 at 1:02 am (1 year ago)

          Our rescue has used Terramyacin Ointment for years and years for cats and kittens with eye infections or “drippy eyes”. However, some vets we have consulted suggested plain saline instead. However, that’s heard to get into their noses. Another suggested we get a product for children called “Little Noses”, too.

  18. Cathy
    January 11, 2016 at 3:38 am (1 year ago)

    Agree; it hasn’t helped my rescue kitty, who has the herpes infection, in over 2 years. I’m sharing the article w/my DVM. Thank you, Ingrid!

  19. Joyce
    January 11, 2016 at 1:09 am (1 year ago)

    Thanks for that Ingrid!! One of my AZ kids was prescribed l-lysine for cold symptoms a few years ago. I don’t really recall it making anything better, and thank goodness it didn’t do any harm that we know of. However, if it happened again, I would’ve just done as the doctor order had I not seen this. As always, much appreciated!!


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