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Lysine and Cats: Why It is Not Recommended

Lysine and Cats: Why It is Not Recommended in Cats with Feline Herpes Virus (FHV)I get asked a lot about lysine supplements for upper respiratory infections in cats.  Lysine and cats seem to come up quite often when discussing a sick cat, in a community cat colony or a home!

Many cat caretakers, shelters, sanctuaries, and vets have recommended lysine supplementation in cats who have Feline Herpes Virus (FHV), a type of feline upper respiratory infection.

I do NOT recommend it for the use of controlling FHV. Why? Because it doesn’t actually work and evidence suggests it makes things worse! Read on for my reasoning!

Disclaimer: I am not a veterinarian and this does not constitute veterinarian advice. Please contact your veterinarian for any health concerns you have for your cats. I simply use my experience and research to help educate cat lovers, feral cat caretakers, and rescuers.

Disclaimer:  This post contains affiliate links.  This simply means I will earn a small commission on qualifying sales at no cost to you.  Read Affiliate Disclosure for full details.  Thanks for supporting the kitties!

What is Lysine?

Lysine is an important amino acid that must be obtained through diet as neither your body nor your cat’s body will make its own lysine. It is used the biosynthesis in proteins. It is also important for normal growth and muscle turnover, and to build carnitine, a substance found in most of your cells!

Now, I’m not going to go TOO technical here, but a quick rundown of what it is might be useful for you.

A lack of lysine can also cause some health issues in humans (and cats!) like defective connective tissues, impaired fatty acid metabolism, and more. Too much lysine, caused by ineffective catabolism, and you can have neurological issues.

It’s a biological thing.

For the purpose of supplementing lysine to help with Feline Herpes Virus (as well as human’s herpes simplex virus (HSV)), it is SUPPOSED to work by limiting arginine, another amino acid. HSV (human herpes) is actually richer in arginine and poorer in lysine, and thus lysine supplementation was tried to help control HSV and later, FHV (feline herpes).

Let’s state this plainly:  Lysine is NOT a supplement for immune support.  It is supposed to be a supplement to fight off the feline herpes virus by reducing arginine.

To be clear, human herpes and feline herpes are NOT the same virus. But they are similar to each other.

Now arginine, in humans, is considered a semi-essential amino acid and can be synthesized by your healthy body. No need to supplement it.

However, cats CANNOT synthesize their own arginine. They MUST get this amino acid through their diet. It is considered an essential amino acid for them. It has been suggested that using lysine to reduce arginine (if it works) can be very dangerous for our feline friends.

Cats are HIGHLY sensitive to arginine deficiency! Arginine is very important to detoxify ammonia, which results from the breakdown of proteins. It also has an important function in the urea cycle. According to WikiVet, “feeding a diet that has no arginine but contains substantial levels of other amino acids can result in death within a few hours.”

In kittens, arginine deficiency can cause diarrhea, weight loss, food refusal, urinary issues, and more!

Tiny Orange Tabby Kitten Face

Does Lysine Actually Reduce Arginine?

Lysine does NOT have antiviral properties and will not improve a cat’s immune system, as I stated previously.  Even if it were effective on the feline herpes virus, it would not work on the various caliciviruses or feline chlamydia or other upper respiratory infection agents.

To put it simply, lysine and arginine use the same intracellular transporter system and thus too much of one may affect the metabolism of the other. Notice that I said MAY affect the other. It is a theory.

So far, I have not found any studies that actually state the arginine is reduced in medical studies. The levels of lysine in the blood increase, but that doesn’t mean levels of arginine decrease throughout the body.

Feline Herpes Virus (FHV)Sick Tabby Cat with Feline Herpes Virus

The feline herpes virus is one of two types of viruses that cause most of the upper respiratory infections in cats. It is not as common as calicivirus, but it does account for a large percentage.

Read more about feline upper respiratory infections here.

FHV and other upper respiratory infections cause sneezing, congestion, runny or inflamed eyes, coughing, or other symptoms like fever, pneumonia and in some cases, death.

What separates FHV from calicivirus is that once a cat has contracted FHV, that cat will be infected for life and have occasional reoccurrence of upper respiratory symptoms. Just like human herpes, sometimes the cat shows symptoms, sometimes they don’t, basically. They are also infected for their entire life and occasionally shedding the virus, thus are contagious to other cats.

Calicivirus on the other hand usually gets the cat sick one time, though they may end up infected for months, years, or their entire life.  Sometimes they may even shed the calicivirus and thus be contagious to other cats.

Just like other herpes viruses, the feline herpes virus is high in arginine. Thus, the theory that supplementing with lysine will reduce arginine and subsequently reduce herpes symptoms, how frequently it happens, and virus shedding, which can infect other cats.

Studies on Lysine and Cats

There are numerous studies that have actually proved that lysine supplementation does NOT prevent or help treat feline herpes virus.

Some studies have actually reported an INCREASE frequency of FHV episodes and virus shedding when cats are supplemented with lysine.

In case you’re wondering, it also not effective for preventing cold sores or other herpes symptoms in humans either!

There are many studies published that have proved that lysine supplementation is completely ineffective in FHV cats and/or INCREASED virus shedding and symptoms.

Here are a couple:

BMC Veterinary Research: Systematic Review

PubMed: Study of Effects of Dietary Lysine Supplementation on Infectious Organisms in Cats in a Shelter

PubMed: Effectiveness of Dietary Lysine Supplement in Cats with Enzootic Upper Respiratory Disease

In fact, only ONE study noted that it helped cats with conjunctivitis symptoms from the herpes virus, but that was a seriously small study of EIGHT (8) cats. That’s 4 cats treated with lysine and 4 cats in the control group to compare the two.

There’s a veterinarian article discussing both points of view about lysine, so you can make your own decision.

Though, if you’re still interested in trying lysine supplements for your cats, you can find some on Amazon or Chewy.

Viruses in a Lab

Do I Recommend Lysine Supplementation for FHV? No

Lysine has no antiviral properties. It cannot even be proven it limits arginine. If it DOES limit arginine, that could be dangerous in cats, as they do not produce their own. There have been studies of it proving it actually made symptoms and viral shedding worse!

The only reason lysine was recommended in the first place was based on a HUMAN study on the herpes simplex virus. And just to say, there is no evidence it reduces cold sores either.

I know vets, shelters, and rescues do recommend it. I don’t.

So no, I don’t use lysine supplements nor do I recommend them for people caring for cats with upper respiratory infections.

What Does Help a Cat’s Immune System?

Let’s be clear, lysine was only suggested for use in feline herpes virus NOT immune system response, despite the numerous products that claim it helps a cat’s immune systems.

The most important thing you can do to help a cat’s immune system is diet, to be honest! The better the nutrients a cat ingests, the better the cat’s overall health is, including the immune system.

In my outdoor cat food post, I recommend the best food you can afford for outdoor cats.  This is still true.  Bad food is still better than NO food, definitely.  That being said, the better the food, the healthier the cats!  So my first recommendation is to save the money you spend on lysine supplements and buy your cats better food!

Another suggestion is probiotics!  There has been some early evidence that probiotics help your overall immune system, not just your gut!  It is suggested that it does the exact same thing in cats!

Another suggestion is that arginine supplements actually INCREASE immune system responses in cats!  That’s the same amino acid that lysine is supposed to reduce!  (Though no evidence shows it does reduce arginine in cats). Another possibility is supplementing with salmon oil as the results are promising for that as well.

My last suggestion for boosting a cat’s immune system is reducing stress!  Stress is a key factor in the reoccurrence of the feline herpes virus as well!

Have you used lysine for FHV? Do you think it helped? Or not? Leave me a comment!


42 thoughts on “Lysine and Cats: Why It is Not Recommended”

  1. Hi Rochelle,

    I tried Lysine a few times and it was not as effective as I expected based on all the recommendations to use it. Now I don’t use it anymore. I stick to diluted apple cider vinegar on my cat’s fur since that is actually anti-viral and works wonders. If it is too bad I get antibiotics from my vet.

    I also give my cats an immunity boosting herbal supplement that gets mixed into their wet food. I am always trying to figure out if I should be giving them extra vitamins, probiotics etc. Right now I am trying a mixture of very high quality cat food with all that mixed in with medium grade cat food and some extra supplements. The food has a mushroom extract that is supposed to work wonders for immunity…but it costs a fortune, hence the mixing it together.

    Thanks for this great information on Lysine for cats. I have to say however, Lysine does seem to take down a cold sore right away for me and my husband. I always assumed it is a different virus in cats however and just doesn’t work on them the same way. In any case, it is great to get more information on Lysine in cats.

    1. Hi, Jessica!

      The human herpesvirus and the cat herpes viruses are different viruses, just similar to each other and the way they behave, I believe. Regarding the human herpes virus responding to lysine, all studies on it have been ‘inconclusive’ from my understanding. The studies that suggest it is effective have never been done in a controlled setting, so they can’t prove it was lysine that helped it.

      The one study I wanted to share with you isn’t working on pubmed right now, but the article about it on the Harvard Medical School site is useful too.

      That’s not to say it doesn’t work! They just have no evidence it does except for a couple of studies that weren’t controlled. Other studies indicate it isn’t effective at all. So more work needs to be done!

      But because of those studies that suggested lysine was effective on human herpes simplex virus is how it started getting recommended on the cat herpes virus. Crazy, right?

      Anyway, glad to see another person who does their research on cat supplements! Thanks, Jessica!

  2. I have read other research and posts that support your claim that lysine is ineffective for treating FHV in cats. I haven’t seen any positive reviews for arginine supplements either. My vet isn’t a big proponent of most animal supplements, he syas they just pee them out without any real affect. I think your recommendation of controlling a proper diet is the best course of action to address the issue. 

      1. Rochelle,

        Sorry, but my experience is very much the opposite!!

        I adopted an orange tabby who developed a condition that could not be diagnosed. The condition was one eye was closed!!! My vet could not treat it and in exasperation suggested we could just remove the eye!!!! But he did refer me to a feline specialist in optical problems. HE didn’t know what to do. At this juncture, I spent close to $900 in vet bills. As a last resort, I tried Lysine. It worked, curing the condition within 10 days!!! So I’m sorry. When I think I was tempted to remove this lovable feline’s eye ( who already had his teeth removed when I adopted him), I cringe. So I say thank God for Lysine. You could be giving other cats and cats owners information that could actually hurt our furry pets.

        1. Hi! Thanks for visiting. However, I’m not giving incorrect information. I’ve cited many studies, linking to them, and other veterinary articles that give evidence lysine had no effect or in one study, made symptoms worse. One anecdotal case of it ‘curing’ a mysterious eye problem doesn’t mean lysine helped. It could have been anything as your cat could have been given other medication, could have had a severe eye irritation that cleared up as soon as the foreign body was removed, or any other such thing could have happened. Only in blind test studies where there is a control group (a group given a placebo so that you can compare the results of the study from the group given the lysine versus the ones given a placebo). Nearly all feline illnesses can get better or worse on their own with no interference from people, which is why they have a control group.

          I’m curious, Lysine is only a supplement. It’s only suggested for the feline herpes virus which is an upper respiratory infection. It wouldn’t work on an unknown eye condition even unless it was runny or swollen shut from the feline herpes virus, IF it worked as people claim. And no vet I know would remove an eye unless that eye was damaged irreparably and useless, making an eye removal an improvement for the CAT. No vet I know would remove an eye from an upper respiratory infection unless that eye had completely ruptured. Not even for an unknown cause.

          Now, whatever caused your cat’s eye to close was never diagnosed. It could have actually been something that lysine actually helped, for whatever reason, and not a feline upper respiratory infection at all. IF that’s what caused the condition to get better. If that’s the case, my statements still stand. I don’t recommend lysine for upper respiratory infections. That doesn’t make lysine supplementation worthless. Maybe your cat was lysine deficient. I don’t know. But nothing you said proves it works on feline upper respiratory infections or the feline herpes virus. Just that you think it helped your cat’s mysterious eye problem.

          I’m more concerned with your vet. I suggest you get a new one if they were wanting to remove an eye for an undiagnosed issue for no good reason.

  3. Hi, I just finished reading some very good points here I think it’s probably the same with pharmaceutical companies for humans they are more interested in making money than people’s health.  That’s probably why they recommend Lysine because of the financial element.   I don’t have a cat myself but I do think this is some very good knowledge your sharing here that could help a lot of people.

      1. Hey Lexie: Your spelling is perfect – better than a LOT of grownups. Good for you for getting info on your own!

  4. I’ve heard a little bit about lysine in cats but to be honest nothing so comprehensive as this, so I appreciate your knowledge on the subject. Sometimes it can be difficult to care for cats especially if you have multiple cats. To be honest it seems sometimes that hospitals and vets are more of a business than a place of healing. It’s straightforwardness such as your post here that will not only help people care for their cats, but also keep the hospitals and vets honest. You’ve convinced me that lysine is not a good choice for fighting the cat’s FHV infection, and that a healthy diet is the best option. My cat friends will love your post, thanks!

      1. Sorry to use the reply like this, but could not find where I could comment directly. This study tested all combinations of lactoferrin, lysine, and antibiotics. “The aim of the present study was to verify the efficacy of lysine alone and of the association lysine-lactoferrin against FHV-1 in cats. …These data suggest that the association lysine-lactoferrin could be a first choice in FHV-1 infected cats for reducing clinical signs and viral shedding.” https://www.researchgate.net/publication/287592386_Evaluation_of_lysine_and_lysine-lactoferrin_association_in_cats_infected_by_feline_herpesviras-1?enrichId=rgreq-97a6d05d23c7cf9d42adebebf8205c0d-XXX&enrichSource=Y292ZXJQYWdlOzI4NzU5MjM4NjtBUzozNzUyOTQwNTA0ODgzMjBAMTQ2NjQ4ODQ4MjIxMA%3D%3D&el=1_x_2&_esc=publicationCoverPdf

        1. Unfortunately, that study does NOT have a control group.

          Here’s the problem with the study. Obviously the group treated with Clavamox ALL got better. The OTHER 4 groups were all treated with some lysine type product. There was NOT a control group that was given NOTHING.

          All this study proves is that 100% of the cats in the Clavamox group got better, while lysine was LESS effective. They just ‘phrased’ it as lysine “COULD BE” be an effective first line of treatment for feline herpes and viral shedding. What? They don’t prove anything except that Clavamox works better.

          See, we need a group that wasn’t given ANY treatment to determine the percentage of cats that recover WITHOUT TREATMENT. Do you know how many cats recover from a herpes outbreak without treatment? That’s what you want to determine. You don’t want to prove Clavamox works better. You want to determine if Lysine works better than NO treatment.

          So don’t prove that Clavamox works better. I want you to prove Lysine cats improved in better numbers than the control group of with a placebo or no treatment.

  5. So you’re the Barn Cat Lady. I love ti. Do you live on a farm and how many cats do you have?

    My Mother’s father had a successful dairy farm in the Stoney Rises of western Victoria, Australia. When I was a kid we usually got their once a year. I loved that place there were all kinds of animals including cats. ferrets rabbits chooks dogs cows and snakes. Carrying a length of fencing wire was a must to kill snakes, but I only ever saw a couple.

    I liked the way you explained lysine that was my first question. I knew a vegetarian couple while I was at university. Vegetarianism was almost a religion for them.  From time to time they would mention how their lyfe style didn’t require the killing of animals. I always thought it was ironic that they had a cat which as you indicated needed protein that humans didn’t. So the cat ate meat. Does a cat have to eat meat?

    I like what you said about diet. I agree the immune system requires an extensive range of minerals. And in addition to a good diet, we all need less stress.

    1. Hi! I actually own 3 cats, I have another 3 cats who live in the barn I care for, AND I have 10 foster cats and kittens!!

      You are absolutely right that cats must have meat. They cannot survive on a vegan or vegetarian diet. If they have a cat, they would have to be buying meat. This is partially why I haven’t gone vegan (although health is the main reason!). It seems a bit hypocritical to me if I went vegan to stop supporting the meat industry, then still purchase cat food.

      Thanks for your excellent comment!

      1. Hi –
        I don’t think it’s hypocritical to care for a cat (or multiple cats) and be vegetarian or vegan. Cats are OBLIGATE carnivores–they MUST eat meat. That’s how they’re designed.
        Humans have a CHOICE. That’s how we’re designed. (Sometimes I think we have TOO MANY choices, and that’s actually a design flaw!)
        But a vegetarian or vegan who chooses that diet for health reasons should understand that, for HEALTH REASONS, they have to feed their cat/s meat.
        A vegetarian or vegan who chooses that diet for non-health reasons should understand that, for HEALTH REASONS, they have to feed their cat/s meat. But they can choose WHAT KIND of meat product/s to give their cat. They can choose only organic, or only humanely raised, etc.
        And, of course, another reason we would feed our cat/s meat products–because we love them!

        1. Hi! You’re right that a cat needs meat and there’s no choice about it!

          I believe I said I’d feel hypocritical and here’s my reasoning.

          If you go vegan for health reasons or because you yourself can’t eat animals, then that’s perfectly fine when you own a cat, who has to eat meat in his or her food.

          If you go vegan because you are morally opposed to the meat industry for animal rights reasons or because of environmental reasons, but then adopt a cat, who forces you to buy cat food with meat in it, which in turn supports the very industry you are against. See what I mean? It’s hypocritical. But if you’re aware of the hypocrisy when you go vegan, then that’s cool too!

          I can’t go vegan for health reasons myself, but if I went vegan, it’d be because of the animals and the environment. Then I’d feel hypocritical. Vegan and vegetarian diets often require some supplementation and both diets have been linked to depression, although they aren’t sure if the diet caused the depression or if depressed people are more likely to go plant-based. I simply chose the least cruel options I can, eat as little meat as possible, and supplement what my doctor recommends. But at least I don’t feel badly about having cats who need to eat meat!

          I’ll have to double-check to see if I explained that as well as I did here.

          Thanks for stopping by!

          1. Greetings!
            I’m a vegetarian and I make raw food for my two cats. I grind the meat myself (16 pounds every two weeks, they’re Maine Coons) and include a nutritional completer, heart, liver and salmon oil. I don’t feel conflicted or hypocritical at all because cats are obligate carnivores and will die without meat. For me, I can live healthy without meat. Hope this helps anyone thinking about feeding meat to pets and their humans being vegetarians. 🙂

          2. I just clarified my comment up there. I didn’t mean that all vegans or vegetarians are hypocritical. But the gentleman mentioned they were treating veganism as a religion and how their lifestyle doesn’t depend upon the killing of animals, but they have a cat… THAT is hypocritical. If someone doesn’t want to eat meat or kill animals to consume themselves, but love cats and understand they need meat, awesome. I’m mostly veggie myself, but I have a horrible vitamin deficiency on a regular diet so already have to supplement already and my doctor vetoed vegetarianism or veganism for me completely unless I go veggie with fish (which I don’t like eating fish, so that’s completely not an option). I have no choice. If I went completely veggie, I’d do it so no animal had to die for me to eat, but I’d understand that by choosing to have a cat, I was still supporting the killing of animals for food. Just supporting the killing of them for cat food. But they definitely can’t run around bragging about their lifestyle not hurting any animals if they have an animal they have to feed meat.

            That’s all I meant by that particular comment. It’s for those that are condemning people as immoral for being unable to go vegan, while at the same time, they have to buy meat for their cats.

            Or they try turning their cat vegan, which isn’t good.

          1. I didn’t call vegans hypocrites. I said “I” felt like a hypocrite because I save cats and was forced to support meat production because I love cats, etc. And it’s responses like this is why I don’t like speaking to some vegans.

            I’m vegetarian, BTW. And I actually failed at being vegan due to health issues as I got seriously ill when I tried after about a year. Once I started adding dairy and eggs, I did much better. Not EVERYONE can go vegan, as nice it would be. There are actual genetic differences where some people can properly get nutrients out of an all-plant diet and some people cannot, because these people lack certain enzymes needed to break down certain nutrients into other nutrients. It’s like being lactose intolerant. Some humans can break down lactose easily, despite not being infants. It’s an evolutionary thing humans started developing after they started drinking cow milk. But not ALL humans can tolerate lactose after they’re weaned from mom.

            Some humans can, and some cannot. And my doctor and I learned I did not do well, even WITH a ton of supplements.

            But I did not say vegans were hypocrites. I said that *I* FELT like a hypocrite. Sigh. Many vegans suffer pangs because they feed their cats meat. It is NOT just me.

  6. Perhaps the science does not know why it helps in some cats (note: obviously not ALL cats, based on what virus is causing the URI or your cat’s individual immune system) — evidence anedotally supports that for many cats it does help. Science is always evolving and changing based on new discoveries. Working in a vet office I can say many cats benifit greatly from Lysine, clearing up URI. Two of my cats in fact could not do without it — within a week they will have sever eye issues and will be sneezing out awful snot if they do not have it. Why does it work? No idea. But they need it.

    1. You’re right. Science and evidence is always evolving based on new evidence all the time. The problem arises from doing studies on cats on lysine versus cats on a placebo. Now cats can’t be fooled by the placebo effect, but a lot of the time, URIs will self resolve on their own as they’re viruses and require the cat’s own immune system to fight off. So we can’t know if the anecdotal evidence is actually due to the lysine or due to the cat’s own immune system. Some cats will definitely get better on it, simply because they would have gotten better without it. That’s why anecdotal evidence isn’t actually considered proof. Especially as the studies I’ve seen have all indicated that lysine performs on par with the placebo test, meaning no increase in resolving symptoms. Admittedly, there’s only one study that suggests it made symptoms worse. AND they’re studying lysine on feline herpes, not on every other type of URI there is out there. And scientific studies on cats are lacking in a lot of ways,so it may be we will find out lysine works on in some unseen way on certain things.

      It’s like ringworm and some rescues and vets are suggesting that the treatment isn’t actually working any faster than a cat who isn’t treated since ringworm almost always self-resolves in cats, no treatment required. Which is a good thing with the barn cats, I can’t imagine trying to bathe them in lime sulfur dips or with anti-fungal shampoo. But there seems to be heavy evidence that treatment is not any more effective and it’s simply the cat’s immune system.

      We don’t know. I know just as many people who agree it didn’t work as swear that it did, and the studies I’ve found agree that it isn’t any more effective than placebo, so that’s why I don’t use it.

      It is up to each individual and their vet to decide for themselves to use it or not to use it, of course.

  7. We adopted a kitten that was diagnosed as having FHV or a URI. She would sneeze awful snot rockets, and her left eye would get all gunky. I tried lysine and another immune booster I read about (forget now what it was) and neither seemed to help much.
    However, I went back to the lysine (I forget why now) and have been giving it to her in her nightly wet food snack and it has since cleared up (for about the past year). She’s become a very picky eater and for awhile I was having a hard time getting her to eat it on a daily basis & her eye did indeed get worse when she wasn’t taking it.
    We have a big 22# long-haired cat (Norwegian Forest cat we think) who often has problems with diarrhea (which makes it so hard for him to stay on top of grooming himself – it’s gross). I’ve tried getting him to eat pumpkin, and coconut oil, to help supplement his diet (didn’t work – he wouldn’t eat it). Got the idea to also feed him the lysine if it’s supposed to enhance immune support. So he too has been eating it for the past 6-9 months and has not had ANY diarrhea issues! This has been a godsend!
    I just got online to see if they can eat it daily, or if now that their problems have cleared up, I should maybe be dialing it back a bit to maybe only 4 or 5 days a week… As I know some things you don’t want to take long term.

    1. Ah, but was it the lysine that helped or was it something else? We can never know if something self-resolved on their own, the lysine did something, or if it was a different thing we tried. That’s why I always look at scientific studies. They compare the results of giving lysine to one group and giving a placebo to another group. The placebo group is the control group. Some animals will improve in the placebo group, but if something works, it needs to do better than the placebo group. Lysine doesn’t perform better than the placebo.

      That said, I have no idea if it is a good idea long-term or not. There actually isn’t a lot of research on it in cats, except the two or three studies that indicate it doesn’t work any better than placebo/no treatment. In one study, it even made symptoms worse. But there isn’t a study on long-term effects that I’ve found.

  8. Thank you for this new-to-me angle on lysine. I was about to give it to my kitty but now I’m going to read more and consider carefully. I do feel obliged to comment on two things: I have had absolutely miraculous results using lysine with my own cold sores (I’m a human, btw), and I astonished my dermatologist with the amazing improvement it accomplished in my shingles. Now he recommends it. It’s inexpensive and harmless for humans at normal doses for a short time, so I truly believe it’s worth trying with any human herpes problem. Secondly, I have been vegan for a several years, vegetarian for almost fifty, and I am not at all depressed or unhealthy, nor are any of the many vegans I know. My cardiologist is blown away at my perfect blood pressure at age 70. I wish I could avoid supporting the meat industry in any way, but having rescued many obligate carnivores in my life (and think of them as my closest friends) I don’t feel I have a choice. I don’t feel that this is hypocrisy, just an unfortunate necessity. I would love to see a pet food company produce a food line that is not only organic but as humanely produced as possible instead of factory-farmed. Thanks!

    1. Hi, Sandy,

      I have no idea if lysine would help with Shingles issues or not, that’s one thing I didn’t research. But here’s the problem with anecdotal evidence. It’s not done in a controlled study where one group of people/cats is monitored taking ONLY lysine for herpes symptoms while another group is given a fake lysine. Then they compare the two groups. Because even in the FAKE group, some people WILL get better. But does taking real lysine actually IMPROVE the results more than the fake group?

      In anectotal evidence as when people swear something happens, they tend to associate one thing with getting better. But we don’t know if it was THAT that helped, the body’s immune system, or even something else they took finally started working. We have no idea. And in people, people can be fooled by the placebo effect. Basically, if someone THINKS they are getting real medicine, they actually FEEL better, even if they were given sugar pills. That’s why they test improvement rates against placebo groups. It helps create a baseline on the average number of cats/people who get symptom improvement with NO medicine versus a group given a medicine. Did more people get better then? Or did the same number of people get better? So I put little stock in people’s experience with it. I’m always reminded about people who SWEAR they got the flu after the flu shot. What’s funny is most of the time, they got sick before the flu shot was even given and they experienced symptoms immediately after the shot. But did the flu vaccine actually give them the flu? Not according to all known vaccine studies. Not a single person caught the flu from the flu shot during clinical trials. But some people SWEAR it happens.

      It’s why I look at the percentage of people who improve with a medicine vs. the group that weren’t given the treatment. Because some cats/people will improve with NO treatment at all and we can’t say for sure whether it was lysine or the immune system that actually helped.

      As for the vegan thing, that’s just how I feel. I also have severe deficiencies on some things even ON a normal diet and have to carefully supplement as it is. My doctor warned me not to go vegan. Some people absolutely CAN and do thrive that way. I just can’t. I do however try using more humane options than factory farming. Free-range chicken eggs and I’ve limited my meat. And many cat food companies will do the same, but it can get pricey. And when you care for dozens of cats, they might not be able to afford ethical cat food. So it’s a toss-up. *I* just feel a little hypocritical that I feed my cats meat by necessity and can’t afford more humane options for them without going completely broke and that I myself can’t thrive on a vegan diet. But anyone that tries reducing the cruelty of their food intake is helping, too, whether by going vegan or even just free-range. The meat industry IS changing thanks to all of that.

  9. Harry Koudounas

    I didn’t know about L-Lysine, until my veterinarian told me, to try, as an adding factor for a serious case I had with a cat of mine.

    But look, that was as a plus only. She said, well you can also try to give some L-Lysine, it may help.

    The cat was found in the neighborhood near to death, dehydrated, with serious weight loss, and serious rhino sinusitis, actually nose and lung infection. Nose liquids, not eating etc.

    That was not FHV. The vet told me as a sinus virus with companion bacteria. We made antibiotic injections (I think 3 times every 2 days), Vet told me that they were Amoxycillin, she also told me to continue with Amoxycillin by mouth (Augmentin), or alternatively with Doxycycline (Vibramycin).

    We continued, the cat started to eat, and get weight every day. But the sinusitis was continuing also.

    We even got lung X-rays, and the X-Ray lab told me that sinusitis may go a chronical problem for life.

    May the inner of the nose, had some distruction by the long time infection.

    I lost my faith, using Augmentin (1 week) or Vibramycin (1 week), for a long time (15 days), until the Vet told me again to insist with Amoxycilline for up to 25 days.

    You may also use some L-Lysine in the food to help, she said.

    We went for the antibiotic cycle for 25 days using an other antibiotic, Amoxil, calculating the doses per kilograms of body weight, and the 12 hour cycle of the doses, with integrity.

    So, the miracle happened, and that so difficult sinusitis vanished!

    To say the truth, I also help the cat with good nutrition and vitamins. So, I can not conclude if the L-Lysine helped or not. But I’m sure my success was the long time (25 days) of the antibiotic cycle, and that for me and my cat, Amoxicillin finally worked.

    Today, it’s sinusitis is gone, but it left some little remain, I hear it, when he sleeps and snores.

    I had many FHV cases with other cats. The key factor is time. Time is critical, to save the eyes, and start antibiotics immediately, also antibiotic eye drops / antibiotic eye cream, we use Tobrex (Tobramycine) as an eye drop antibiotic.

    Or if you have a serious case, you go to the vet for antibiotic injections as the start of the therapy, and you continue antibiotics by mouth, and eye drops.

    The tragedy is always, if you lost time, and you lost an eye, or the worst, both of the eyes. But in some cases, the cat can be saved with a medium eye damage, but she will have vision after all.

    My conclusion is: L-Lysine may add some help (?) but the basic is the antibiotics, both for the body, and for the eyes (drops).

    And of course, enforcing the cat with nutrition, vitamins, fish oil etc.

    1. Absolutely! L-lysine is often used instead of medication. Of course, as long as proper meds are used as well, it’s not harmful and ‘may’ help. Just at this time, there’s no evidence it helps the feline herpesvirus, but that doesn’t mean it isn’t beneficial or effective for other issues, just they haven’t studied it.

  10. I have a cat that came from the shelter with some sort of URI, his eye got gunky and he sneezed bad. The vet said it was FHV by never ran tests so take that with a grain of salt. They sent me home with a l-lysine paste to give him and he did get better. I agree he might have gotten better on his own. However, fast forward in time and he had flare ups. I didn’t believe the l-lysine helped, but I finally felt bad for the guy. He be miserable for a few weeks every time he has a flare so I bought some. Wow! He cleared up in one to two days of his first dose of the stuff, and if I stopped giving it to him too far the flare up comes back. I have no idea why it works or if he even has FHV for real, but it does work for him, and I used it on a pair of feral born kittens in my yard and they cleared up too. Take the info or leave it, but I’m going to use it because I can’t stand listening to my poor guy sneeze, shake his head, and mope around miserable. The vet also recommended having him get shots for FHV regularly but he is so traumatized by going to the vet and the l-lysine world better than more shots ever did.

    1. Hi, Dawn,

      Some people swear by L-Lysine. It did nothing to help mine. So I decided to research studies on it. That’s when I realized ALL the studies they’ve done show it performs no better than the control group who is on a placebo! In humans or cats! That’s when I made my decision.

      But here’s my other problem with L-Lysine supplements. It was recommended for FHV only, right? (And yes, your vet diagnosing without doing lab tests to determine if he or she is right isn’t very cool. MY vet doesn’t recommend those tests all the time either, but he calls all of those types of illnesses, upper respiratory infections or URIs. He doesn’t suggest WHICH type of URI it is without doing lab work. He usually just treats the secondary infection with antibiotics and waits for the cat’s immune system to fight off the virus. If that doesn’t work, THEN he suggests those tests.) But then these people decided to make MONEY off of L-Lysine and started marketing it for IMMUNE support, instead of marketing for what doctors were hypothesizing it would do for the herpesviruses. The ONLY studies I’ve seen that support L-Lysine usage is for those people who are lysine deficient! Everything else is a “eh, maybe?”

      Here’s my other problem: supplements are not regulated by the FDA or any agency until AFTER a complaint has been made and the FDA tests the product to be sure the product doesn’t contain actual drugs, prescription or otherwise, or other ‘hidden’ ingredients not included on the label. So who’s to say the supplement company didn’t add something extra to that lysine, like antibiotics or antiviral medications, to help it fight off severe URI symptoms. We don’t know. By law, they’re not supposed to. But there are hundreds of supplements that have been pulled off the shelves by the FDA after it was found to contain prescription drugs, illegal drugs, or other problematic ingredients without proper labeling. You think I’m kidding, but I’m really not. Male enhancement and weight loss products are the two most common ‘supplements’ that companies will include prescription drugs in them to make them actually work JUST to make money. I do a LOT of research on supplement companies before I choose one for myself, let alone my pet.

      But yeah, it may have worked for you and maybe it was legitimately lysine, and maybe it was the cat’s immune system as well as any other meds the vet prescribed. Anecdotal evidence gives us hints onto things to study, but it’s not accepted as proof scientifically. By all means, keep using it if it’s working. Maybe your cat is just lysine deficient and that’s why it helps! In which case, great.

      But it didn’t work for me and all studies I could find testing lysine on FHV indicate it doesn’t perform any better than a placebo. Add in my irritation on their marketing practices and lack of trust in companies who deal in supplements, I still don’t recommend it. ^_^

  11. My 18 year old cat was sneezing heavily for a whole year. It was on the walls, the furniture, ouch … I tried everything from herbs (ginger, thyme, spirulina, echinacea, vitamin c …) to massage and (even more) stressfree living. He was always fed grainfree wet food, never any dry food, and still is. So his food has always been pretty good. About a year ago I tried l-lysine with vitamin B6 (excellent combination) and the sneezing stopped within 2 weeks! The sneezing never returned. He since gets a tiny maintenance dose daily. As I write this I have a happily content non sneezing cat purring on my lap. Since a few weeks I give him some good quality probitics. He’s on his way to 19 and still jumping high … literally and figuratively. Just wanted to share my experience.

  12. We adopted a stray cat from a strip mall my daughter was working at. He was frequently seen in the garbage bin behind the Chinese restaurant, and she and employees would feed him cat food. Winter was coming and she asked if she could bring him home. He stayed in the dog crate in the garage, and we took him to the vet asap. He got his shots, they plucked the ticks off, applied flea meds, etc. Vet noticed his eyes and nose was runny, and told us to buy lysine and crush tablets into powder and sprinkle on food. He was 9 lbs. His runny eyes and nose cleared up and needed no further treatment, and that was exactly ten years ago. There is an article that explains how this works. Viruses need arginine to replicate. Arginine and Lysine have similar properties and viruses latch on to Lysine if it is present in sufficient quantity, and this lowers virus replication so the immune system is not so overwhelmed that it cannot work properly. Meanwhile the arginine is used by the cat as it is a necessary nutrient. There is a scientific report that explains this a at Whole foods magazine, or just Google “Lysine halts coronaviruses”.

    1. If you had read the article, I explained how it is THEORIZED to work, because by flooding the system with lysine, the arginine rich virus wouldn’t replicate, they THOUGHT. And it’s only supposed to be effective against the feline herpes virus, in THEORY.

      Which is NOT a coronavirus, btw. Feline coronavirus causes diarrhea and rarely FIP, nothing to do with any feline upper respiratory infections. Whole Food Magazine isn’t a scientific journal studying medicine, either. They are very biased on what they claim with no evidence. Whether or not lysine helps with coronaviruses has not been sufficiently studied or proven.

      In ALL lysine clinical studies on actual cats with feline herpesvirus, it doesn’t work. One study actually found it made symptoms worse.

      One cat improving while taking lysine proves nothing. Most upper respiratory infections in cats are caused by different viruses, not necessarily just feline herpes. You don’t even know which feline virus caused the illness. AND cats usually get better on their own from upper respiratory infections, just like humans recover from colds on their own.

      You cannot know for sure whether the cat’s own immune system did it’s job, it was something else you gave her, or it was the lysine.

      Since the cats in lysine studies were separated into two study groups: one group got fed lysine, one group got fed a placebo or fake lysine. BOTH groups had some cats get better. BUT the lysine group did not have MORE cats improving than the placebo group. They had the SAME percentage of cats improving! That’s how you tell if something is not effective. If more cats aren’t getting better than fake stuff, obviously it doesn’t work.

      Let’s put it this way. No medicine is 100% effective in all individuals. In order to determine, say, benadryl relieves allergy symptoms, they get a bunch of people with allergies together that aren’t allowed to take anything but what the study gives them. They then split the people into 2 groups. 1 group gets benadryl. The other group gets a placebo or fake benadryl, but they are NOT told its fake! Then they see how many people’s symptoms are reduced in each group. If more people are not suffering from allergies in the benadryl group than the fake group, then it works! If the 2 groups have the same number of allergy relief, benadryl is NOT effective. Because benadryl doesn’t work on everyone, there needs to be MULTIPLE people getting it and because people get better on their own, there needs to be a fake group to make sure there’s a baseline of improving with no treatment.

      Same thing was done with Lysine. It did not improve more cats than the fake lysine group did. Thus, doesn’t work.

  13. I had a 6 months old kitten that couldn’t get rid of conjunctivitis due to FHV. I gave her L-lysine in her food for several weeks – can’t remember dosage. She developed acute kidney failure and she died. When I read about a study with rats and L-lysine, it causing kidney failure, I’m afraid I’ve caused her death. I’m not keen on any supplement anymore, just invest in very healthy food and try give them a stressfree home.

    1. Hi, Ingrid,

      I am so sorry for your loss! I believe you mean this study of lysine and other amino acids. You’re absolutely right that high doses of lysine have caused renal failure all by itself in rats. Considering cats are often prone to kidney problems as it is, this IS something to consider! There is no concrete evidence that lysine causes kidney problems, but there IS evidence that cats with existing kidney problems don’t get lysine out of their systems well. Lysine can also cause allergic reactions.

      Another thing to consider is that supplements are NOT regulated carefully like medications are! To be honest, we have NO idea what is in most supplements on the shelf! Supplements have often been pulled off the shelves AFTER it’s been found to include well-known prescription drugs like diet medications and erectile dysfunction medication, things like that. So if you don’t trust the company, you shouldn’t try that supplement. For all we know, these lysine supplements people are feeding have antibiotics in them, being given in inappropriate amounts and THAT is why it works on their cat. We have no clue. Once I learned how anyone can market a product as a ‘supplement’ and it is only regulated AFTER the FDA decides to test the product on the shelf, who knows how many years after it started being sold, I’ve been very, very leery of supplements myself. At least with medications, you KNOW it’s regulated, that is what you’re getting, and you know it’ll probably work. And if you have a bad reaction, you can say, “I won’t take that medication again” and just avoid it. But supplements can contain ANYTHING. They absolutely can be pulled off the shelf by the FDA. But by then, it may be too late for some people. Or cats.

      I’m sincerely sorry for your loss. I don’t know if it was the lysine, something within the lysine, or the kitten had a congenital kidney issue (the Kitten Lady has one with kidney problems since birthright now) or what, and we can’t prove it with science right now, but you brought up a very good point that lysine HAS been proven to cause kidney issues in rats at high doses.

      Everyone likes to assume ‘supplements’ are safer than drugs. They aren’t. I’d love it if lysine worked for URI symptoms of feline herpes. I really would save SO much on vet bills. But the idea of it already made me leery when there is no proof it works. The idea that it may also cause kidney failure? Super scary!

      Thank you for sharing your story!

  14. Dr Joseph Carlson

    Lysine absolutely is anti-viral… that’s why it works great for people with shingles (Herpes Zoster), cold sores, the flu, etc, etc especially if taken at the first indication of any flareup (and especially as a prophylactic)… it’s also why it’s often the only active ingredient in the medicine vets prescribe for URIs in cats (the rest is just fillers and flavorings). The science isn’t going to change on that any sooner than the science of water being wet is going to change; lysine always was and always will be anti-viral, it’s just which viruses it has an effect great enough with to notice a difference, and with cats you almost always notice a huge difference in just a couple days. Lysine has proven to help with literally millions of cats for many decades and most of those occurrences certainly would not have cleared up within a couple days like they often do with lysine.
    You should stop giving advice on things you clearly know very little about because wrong information is often worse than no information.
    I’m assuming you’ll either delete this or not display it in the first place (whatever, it’s your sandbox (or litterbox – lol) so it’s your rules), but at least spend 5 minutes to find out for yourself whether or not you were wrong (you were) and if you’re relaying wrong information (you were).

    1. Give me ONE study where lysine performed better than no treatment. Just one. It can be human, cat, or guinea pig for all I care. It is studied almost exclusively with herpes viruses in cats and humans, but if you can give me a study where lysine was used to treat ALL SORTS of viruses and WORKED against ‘no treatment’ control group, I am ALL ears.

      See, you can’t disagree with my assessment of scientific studies without actually GIVING me a scientific study to contradict what I’m saying.

      I don’t honestly care if lysine works or not, that’s what you all don’t seem to understand. I would LOVE for it to work, less money on vet bills, just give them lysine! But I canNOT find one SINGLE STUDY where lysine worked better than a placebo/control group. So if you want to change my opinion, that’s how you do it.

      Opinions don’t matter to me. It’s unbiased studies that I’m looking at.

  15. As with most studies, researching your bias, what you want the result to say; will be just as anecdotal as the evidence against your theory.
    And no, pharmaceutical companies are not trying to push natural remedies to anyone; they’d rather you pay top dollar for antivirals.
    Humans have had a lot of success using L-lysine for HSV.
    This is an opinion piece, backed by cherry-picked research and could send humans down the wrong path, not only for their kitty, but for themselves.
    I noticed, if people agree, oxytocin boost! “Thank you!!!!” Rainbows and kittens, if someone disagrees, you’re not thrilled about it, don’t research further, research against your bias, and type paragraphs about how you’re right.
    I won’t be coming back; I just hope with others’ and my own comment, people will ask their vet and/or doctor and do their own unbiased research. Thank you. Take care.

    1. Hi, Boognish,

      If you can link ONE study where there is ACTUAL evidence of human OR feline herpes actually getting BETTER with L-Lysine, then you are more than free to give me that link. You’re disagreeing WITHOUT proof. Give me the proof it works, without saying, “I tried it and it worked for me!” I mean actual scientific studies where there was a noticeable improvement in herpes symptoms with l-lysine. Just give me ONE published study! Just one, from cats OR humans!

      See, I don’t actually care if l-lysine works or not. I had NO opinion on it when it was first suggested to me. I just did my research to determine if I wanted to try it or not. That’s all. I didn’t decide NOT to try it and THEN find studies, like you are suggesting.

      I’m not even against natural cures! AS LONG AS THEY WORK! Many of today’s medicine comes from nature! Aspirin, narcotic pain medication, some antiviral medications, etc, etc, etc. All of those substances we call medicine was usually first ‘discovered’ in nature. But science decided to make willow bark into a more concentrated form and now we have aspirin! Way more effective than brewing willow bark tea and much stronger than the tea. But the EXACT SAME INGREDIENT!

      So no, this isn’t an opinion. I am just against pushing a product that doesn’t work. If it actually worked, I’d suggest it to people, as I do with diatomaceous earth in carpets for flea infestations. But since l-lysine doesn’t work, I don’t.

      I looked at ALL studies that I could find, that isn’t cherry-picking anything. I didn’t ignore the evidence I didn’t like. I DID NOT FIND EVIDENCE! I found evidence of it not working better than a placebo.

      I literally GAVE you scientific evidence of studies and YOU are choosing to ignore that evidence in favor of YOUR opinion. THAT is exactly what cherry-picking evidence is. Not me.

      And everyone should talk to their veterinarians about their cat’s health prior to doing anything. But just like human medicine, some veterinarians have looked at the studies and agree it doesn’t work any better than a placebo and some vets haven’t seen the studies yet.

      And there IS one study that suggests l-lysine actually made the symptoms worse in cats, so I wouldn’t say it was ‘harmless’ to try either.

      But seriously, if you disagree, that’s fine, but you gotta give me proof before you insult people for stating facts that YOU don’t believe. And by proof, I mean unbiased peer-reviewed scientific studies. Just find ONE and I’ll take the article down until veterinarians can decide if it works or not.

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