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Lysine for Cats

Chelsea McGivney, DVM, Nestle Purina Pet Care

Cat and Vet.


Reading Time: 4 mins, 17 secs.


In the past, administering L-lysine to cats was thought helpful. Specifically, L-lysine was thought to fortify the immune system and ward off respiratory infections. Moreover, L-lysine was thought to treat symptoms of the feline herpes virus, or in other words, FHV-1.


L-lysine for cats was thought to relieve: 
  • Respiratory issues: panting, coughing, difficulty breathing
  • Conjunctivitis (inflammation of the conjunctiva) 
  • Sinus issues: sneezing, congestion, sinus discharge
  • Lethargy
  • Fever
  • South throat
  • Cold sores, fever blisters, and mouth sores
  • Appetite loss


Lysine for Cats Dosage


Oral L-lysine (250mg twice a day) was surely one of the most common treatment options for recurring FHV-1 flare-ups. In addition, veterinarians frequently prescribed L-lysine for cats. Chiefly, for the purpose of significantly decreasing symptoms of respiratory infections.


The assumption was that the amino acid reduces the symptoms and prevents future flare-ups. Previously, Veterinarians thought L-lysine interfered with the FHV-1 virus replication. In particular, L-lysine was thought to interfere with the uptake of the amino acid, arginine.


Why is L-lysine beneficial for cats?
  • Supports the immune system, for the most part, by helping treat the symptoms of a respiratory infection.
  • Naturally treats illness by alleviating symptoms and furthermore, preventing future flare-ups.
  • L-lysine is an organic compound, which every cat surprisingly has, but then again, some especially don’t have enough of it.
  • On balance, the feline herpes virus needs the amino acid arginine to reproduce. In any event, lysine is an amino acid. With this in mind, it was thought to ‘trick’ the virus, as a result not letting it reproduce and replicate.


Lysine for Cats: Questionable Benefits


In sum, recent research contests L-lysine as non-beneficial. Particularly in treating cats with feline herpes virus which significantly opposed what was previously believed.


Notably, The Merck Veterinary Manual states, “Previously lifelong oral L-lysine (250/500 mg per day) was recommended to help prevent or reduce the severity of feline herpes virus infections. However, recent work has shown that oral L-lysine can exacerbate the feline herpes virus.”


Furthermore, in 2009, an article published in the American Journal of Veterinary Research examined 261 cats, with attention to determining dietary lysine supplementation. Hence, they found Lysine bore no influence on controlling or preventing infectious upper respiratory disease among cats.


In this case, the study significantly reveals L-lysine as an ineffective management tool. Chiefly it doesn’t treat symptoms or flare-ups of FHV-1. Ultimately, it worsens the infection.


In fact, in 2015, the BMC Veterinary Research Journal published a similar study. In the final analysis, the study found the treatment of FHV-1 with L-lysine is indeed ineffective.


Why L-lysine for cats does not support FHV-1 treatment/prevention:
  • For one thing, trials have failed to prove the efficacy of L-lysine supplements.
  • Studies have chiefly shown lysine for cats has no have antiviral properties.
  • Research reports lysine lowers arginine levels. Since cats can’t synthesize the amino acid themselves, arginine deficiency can result in hyperammonemia.
  • By all means, no studies truly show that intracellular arginine is ever at low enough levels to actually inhibit the synthesis of FHV-1.
  • To demonstrate, in vitro studies with FHV-1 do not chiefly show an inhibitory effect of excess L-lysine on viral replication.
  • In fact, an L-lysine allergy may occur all the sudden. For instance, causing a cat to consequently experience uncomfortable side effects.


What are Lysine’s Side Effects?


In short, there is the conflicting research of L-lysine. On the negative side, there’s also the notion that a L-lysine allergy is all in all possible if the immune system overreacts. In effect, the skin becomes inflamed and as a result, itches. To resolve a L-lysine allergy, remove L-lysine altogether from the cat’s diet altogether.


Possible side effects of L-lysine in cats:
  • Nausea, vomiting
  • Scratching, Itchiness, licking, biting of the skin
  • Seizures
  • Pale gums


Texas feline practitioner Gary D. Norsworthy, DVM, Dipl ABVP, who co-edited ‘The Feline Patient, 4th Edition,’ said, “Some cats have a convincing response despite what science says. I do not recommend it as a first-line treatment for feline herpes virus, but I also do not discourage it… Its use should be on the cat’s response, whether scientific or not.”


Lysine for Cats FAQs


QUESTION: By and large, can the Feline Herpes Virus be confused with other illnesses?

ANSWER: Surprisingly, estimates 90 percent of cat respiratory infections are a result of the herpes virus. Or surprisingly, on the other hand, a cat could also be experiencing a similar virus known as, Calicivirus.


QUESTION: Generally speaking, what causes FHV-1 to flare-up?

ANSWER: On the negative side, Feline Herpes Virus flares usually, as a result of stress or anxiety. According to The Textbook of Veterinary Internal Medicine, “…After a stressful event, the virus reactivates in carriers, and they can affect other animals. Stresses can induce virus shedding, including a change of housing, kittening, etc. Some cats show clinical signs during a reactivation episode, which is a useful indicator they’re likely to be infectious.”


QUESTION: Overall, isn’t L-lysine thought to suppress FHV-1 in due time?

ANSWER: At the present time, authors David Maggs, BVSc, Mark P. Nasisse, and Philip H. Kass, DVM, PHD state their study specifically finds, “Fewer cats and eyes were affected by conjunctivitis. The onset of clinical signs of infection was delayed on average by 7 days in cats receiving L-lysine. Compared with cats in the control group. However, significant differences between groups were not demonstrated.”


Lysine Supplements for Cats


QUESTION: To sum up, do studies fail to demonstrate L-lysine effectively treats FHV-1?

ANSWER: Indeed, studies as shown above contest L-Lysine as an effective means for treating FHV-1. Whereas, the Textbook of Veterinary Internal Medicine states, “The two main causes of viral respiratory disease in cats are feline herpesvirus FHV-1 or feline calicivirus FCV. FHV-1 generally induces a more severe disease than FCV…”

“FHV-1 causes upper respiratory tract disease [URT] with oculonasal discharge, conjunctivitis, sneezing, and sometimes hypersalivation and coughing….The primary treatment involves supportive therapy… Robust evidence that orally administered L-lysine ameliorates the signs of FeHV-1 infection is lacking…”


QUESTION: All things considered, does lysine have no side effects?

ANSWER: It’s important to realize that first, Lysine lowers arginine levels. Second, it can cause allergic reactions. Plus, it has research negating its effects.


QUESTION: Given these points, is L-lysine no longer the forerunner in treating FHV- 1 at the present time?

ANSWER: In brief and to summarize, Dr. Jennifer Coates of PetMd expressly expressly wrote, “It will be hard for me to continue to endorse the use of lysine in the face of this recent article. I guess, I’ll now have to lean more heavily on my other recommendations:

  1. Practice aggressive preventative medicine and treat health conditions that do develop quickly to avoid “distracting” the immune system.
  2. Treat especially severe flare-ups with antiviral medications and secondary bacterial infections with antibiotics.
  3. Reduce exposure to whatever is stressful for the infected cat.
  4. Most importantly, provide excellent overall nutrition to support the immune system. “


 FHV-1 and Lysine Alternatives


For one thing, when it comes to L-lysine and that the management of feline herpes virus, to be sure, there are other choices available.

  1. Use Probiotics: All in all, upkeep a feline’s digestive system by incorporating Fortiflora into the cat’s meal.
  2. Mix in Healthy Toppers: Ensure all the minerals and vitamins a cat needs to specifically upkeep their health are essentially in their diet.
  3. Consider Bovine Lactoferrin: For the most part, Bovine Lactoferrin is namely known for its antibacterial, antiviral, and anti-allergic properties.
  4. Try Famciclovir: Generally speaking, Famciclovir markedly helps stop the replication of the feline herpes virus with attention to reducing symptoms.
  5. Blend Catnip into a Dish: For the most part, a pet parent can certainly relax their cat particularly by sharing catnip into its dietary regimen.
  6. Create a Calm Home Environment: Obviously, maintaining a stress-free home environment, significantly and truly supports your cat’s health in the long run.


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