L-lysine is an essential amino acid, but a cat’s need for dietary lysine does not establish that an extra supplement treats sneezing, eye problems or feline herpesvirus. This distinction matters when choosing between a balanced diet, a supplement and treatment for a sick cat.
Updated September 28, 2026. Sources reviewed editorially; this article is not an individual veterinary assessment.
Does lysine help feline herpesvirus?
A systematic review of lysine and feline herpesvirus found no evidence supporting supplementation for preventing or treating infection. It also identified concerns in some of the available studies. Marketing descriptions such as “immune support” should not be presented as proof that a product prevents illness or resolves an active infection.
In a controlled shelter study, the amount of dietary lysine tested did not successfully control infectious upper respiratory disease. Evidence from a particular study is not a dosing instruction for a pet at home.
What to do about sneezing or eye symptoms
Ask your veterinarian to assess persistent or worsening symptoms. Describe when they began, any eye discharge, changes in appetite or behaviour, and contact with other cats. Bring details of all foods, medicines and supplements. An online product comparison cannot determine the cause of your cat’s symptoms.
If a veterinarian has already prescribed a treatment plan, discuss the evidence and the purpose of each product with that practice. Do not replace treatment with a lysine supplement on the strength of a retailer’s description.
Should you give lysine every day?
We do not recommend routine extra lysine as a general respiratory-health treatment. Nutritional adequacy and treatment are separate questions. Cornell’s feeding guidance explains how to choose a complete diet; adding supplements is not automatically an improvement.
Dosage, gels, powders and chews
This article does not provide a universal kitten or adult dose. The number printed on a scoop, chew or tube describes that product, not a treatment plan. Different formulations also contain different additional ingredients. If your veterinarian recommends a specific preparation for a specific reason, ask for written instructions and when its use should be reviewed.
Before buying, ask what evidence supports the intended use, what outcome you should expect, and whether the product is needed at all. Convenience, flavour and cost are secondary to that decision. A general supplement blend is not interchangeable with a prescribed medicine.
Questions to ask your vet
- What is the likely cause of the symptoms?
- Does this cat need diagnostic tests or treatment?
- What evidence supports any proposed supplement?
- When should I call again if symptoms continue?
Continue with our cat health articles or the Ragdoll care guide. Supplement use should be based on the individual cat, not its breed or coat colour.