L-Lysine for Cats


L-lysine is a dietary supplement used to prevent or treat herpes. Feline herpes virus infects up to 90 percent of cats, causing flu-like upper respiratory infections (URI) and conjunctivitis, a painful eye disorder that may lead to blindness. Feline herpes is contagious among cats, but cannot spread to humans.

Herpes- Induced Illness in Cats

  • Although herpes is a main cause of feline conjunctivitis and URI, other viruses and diseases create similar symptoms. Consult a veterinarian to confirm diagnosis before treating.

    In conjunctivitis, herpes infects cats' eyes, making them swollen, irritated, red, itchy, dry, cloudy and painful. URIs cause discharge from nose or eyes, sneezing, mouth or throat sores, fever, diarrhea, vomiting, lethargy, appetite loss, panting or difficulty breathing, dehydration, congestion and discomfort.

Herpes Remains in Your Cat's Body Permanently.

  • Cats without symptoms still carry the contagious herpes virus, and may have outbreaks throughout life. When stress (illness, crowding, fleas, poor diet, temperature extremes) undermines your cat's immune system, the herpes virus emerges from hiding within your cat's nervous system to cause illness.

How L-lysine Theoretically Works

  • L-lysine is an amino acid similar in structure to the amino acid arginine, which feline herpes virus requires for reproduction. Theory supporting L-lysine supplementation suggests that feline herpes viruses connect more readily with L-lysine than with arginine. L-lysine supplements may lead to lack of viral connections with arginine, forcing viruses to stop reproducing and sparing your cat from herpes.

L-lysine Critics

  • In their 2008 study at the Humane Society of Indianapolis, Tina Rees, PhD, and veterinarian Janet Lubinski found L-lysine supplements did not prevent feline conjunctivitis or URI. They suggested infection control (isolation) and stress reduction as more effective alternatives.

Mixed Results

  • In 2001, veterinarian Mike Richards stated L-lysine supplementation interferes with feline herpes virus reproduction and may be helpful for treating conjunctivitis in some cats. He did not recommend it for treating chronic feline URIs. Veterinarian Wendy Brooks also found L-lysine useful for conjunctivitis, but ineffective against URIs.

L-lysine Endorsements

  • Holisticat.com host Sandy Arora recommends L-lysine supplements as "very effective" for "all cats with URI symptoms even if not officially diagnosed with herpes." Similarly, Veterinary Products Laboratories claim their L-lysine paste, "helps maintain respiratory and eye health, manage inflammation and support the immune system."

L-lysine Warnings

  • Effectiveness of L-lysine for preventing and treating feline herpes, proper dosage and whether long term L-lysine use is safe for cats are still subjects for debate. Consult your cat's veterinarian before supplementing.

    According to veterinarian Wendy Brooks, it's important to ensure your cat's L-lysine supplement is free of the preservative propylene glycol, which may cause feline blood disorders. She recommends L-lysine only as a supplement, not a substitute for medication or veterinary treatment for herpes-induced illness in cats.

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