Lysine for Cats

by catfood

Historically, it was thought that giving L-lysine to cats would help to strengthen their immune systems and prevent respiratory infections, specifically feline herpes virus, also known as FHV-1.

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

Lysine for Cats Dosage

Oral L-lysine was one treatment option for recurring FHV-1 flare-ups (250mg twice a day). Veterinarians frequently prescribe L-lysine to cats to treat respiratory infections because the amino acid is thought to relieve symptoms and prevent future flare-ups. Veterinarians previously thought L-lysine interfered with FHV-1 virus replication by interfering with arginine uptake.

Why is L-lysine beneficial for cats?
Supports the immune system by helping treat the symptoms of a respiratory infection.
Naturally treats illness by alleviating symptoms and preventing future flare-ups.
L-lysine is an organic compound, which every cat has, but then again, some especially don’t have enough of it.
The feline herpes virus needs the amino acid arginine to reproduce. Lysine is an amino acid, which was thought to ‘trick’ the virus by not letting it reproduce and replicate as efficiently.

Lysine for Cats: Questionable Benefits

According to new research, L-lysine may not be as effective in treating cats with feline herpes virus as previously thought.

According to the Merck Veterinary Manual, “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 research has shown that oral L-lysine can aggravate the feline herpes virus.”

According to a 2009 study published in the American Journal of Veterinary Research, dietary lysine supplementation had no effect on controlling or preventing infectious upper respiratory disease in cats. This study went on to show that L-lysine was ineffective in treating FHV-1 symptoms or flare-ups, and may even worsen the infection.

The BMC Veterinary Research Journal then published a study in 2015 claiming that L-lysine is ineffective for cats.

Why L-lysine for cats does not support FHV-1 treatment/prevention:
Trials have failed to prove the efficacy of L-lysine supplements.
L-lysine does not have antiviral properties.
L-lysine undesirably lowers arginine levels, and since cats can’t synthesize the amino acid themselves, an arginine deficiency can result in hyperammonemia.
No studies show that intracellular arginine is ever at low enough levels to actually inhibit the synthesis of FHV-1.
In vitro studies with FHV-1 do not show an inhibitory effect of excess L-lysine on viral replication.
A L-lysine allergy may occur causing uncomfortable side effects.

What are Lysine’s Side Effects?

Aside from the contradictory L-lysine research, an L-lysine allergy can be dangerous because the immune system overreacts, causing the skin to become inflamed and itchy. The cause of an L-lysine allergy is quickly identified and resolved by removing L-lysine entirely from the cat’s diet.

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

“Despite what science says, some cats have a convincing response,” said Gary D. Norsworthy, DVM, Dipl ABVP, co-editor of ‘The Feline Patient, 4th Edition. Moving, kittening, and other stressful situations can result in virus shedding.”

Lysine for Cats FAQs

QUESTION: Is there anything else that could be mistaken for the feline herpes simplex virus?

ANSWER: According to, herpes virus or a similar virus known as Calicivirus cause 90 percent of cat respiratory infections.

QUESTION: What causes an FHV-1 outbreak?

ANSWER: According to The Textbook of Veterinary Internal Medicine, “…After a stressful event, the virus reactivates in carriers, and they can infect other animals.” I wouldn’t recommend it as a first-line treatment for feline herpes virus, but I wouldn’t rule it out either… Its application, whether scientific or not, should be based on the cat’s response. Some cats exhibit clinical signs that indicate they are likely to be infectious during a reactivation episode.”

QUESTION: Does L-lysine suppress FHV-1?

ANSWER: According to the study’s authors, David Maggs, BVSc, Mark P. Nasisse, and Philip H. Kass, DVM, PHD, “conjunctivitis affected fewer cats and eyes.” The onset of clinical signs of infection was delayed by an average of 7 days in cats given L-lysine. In comparison to the control group of cats. However, no statistically significant differences between groups were discovered.”

Lysine Supplements for Cats

QUESTION: Is there evidence that L-lysine effectively treats FHV-1?

According to the Textbook of Veterinary Internal Medicine, “the two main causes of viral respiratory disease in cats are feline herpesvirus FHV-1 or feline calicivirus FCV.” FHV-1 is a more serious disease than FCV…”

“Upper respiratory tract disease [URT] caused by FHV-1 is characterized by oculonasal discharge, conjunctivitis, sneezing, and, in some cases, hypersalivation and coughing….

The primary treatment is supportive therapy… There is insufficient evidence that orally administered L-lysine alleviates FeHV-1 infection symptoms…”

QUESTION: Does L-lysine have any side effects?

IS IT TRUE OR FALSE? L-lysine reduces arginine levels, can cause allergic reactions, and has been shown to be ineffective in studies.

“We recommend that lysine supplementation be discontinued immediately due to the complete lack of scientific evidence of its efficacy,” study authors Sebastiaan Bol and Evelien M. Bunnik wrote.

QUESTION: Is L-lysine no longer the first-line FHV-1 treatment?

ANSWER: “It will be difficult for me to continue to endorse the use of lysine in light of this recent article,” says Dr. Jennifer Coates of PetMd. I guess I’ll have to rely more on my other suggestions now:

  1. To avoid “distracting” the immune system, practice aggressive preventive medicine and treat health problems as soon as they arise.
  2. Reduce the stressors that the infected cat is exposed to.
  3. Above all, provide high-quality overall nutrition to support the immune system.
  4. To treat particularly severe flare-ups, antiviral medications should be used, and antibiotics should be used to treat secondary bacterial infections.

FHV-1 and Lysine Alternatives

Consider the following alternatives to L-lysine in the treatment of feline herpes virus.

  • By incorporating Fortiflora into the cat’s diet, probiotics can help the digestive system.
  • Toppings for a Healthy Diet: Ensure that a cat’s diet contains all of the minerals and vitamins that they require to stay healthy.
  • Consider bovine lactoferrin’s antibacterial, antiviral, and anti-allergic properties.
  • Consider Famciclovir, which inhibits the replication of the feline herpes virus while alleviating symptoms.
  • Include Catnip in a Dish: To improve your cat’s mood, incorporate catnip into its daily routine.
  • Make Your Home More Relaxing: Maintain a stress-free environment in your home to benefit your cat’s health.

Wondering about My Adopted Cat Eats Constantly? Check it out on our latest post!


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