Major Uses

Lysine is an essential amino acid that is sometimes administered to cats to halt replication of the herpesvirus. The amino acid is effective against eye conjunctivitis that is associated with herpes virus infections in felines. Lysine may also be used in dogs.

Lysine works against herpe svirus by coating the virus and interfering with arginine, another amino acid needed by the virus to replicate. Because lysine is an essential amino acid, it must be taken in though diet or supplementation. It is not produced by the body.

Common Precautions

When used as directed, side effects are not typically associated with lysine use.

It is not known if lysine is safe for use in pregnant and lactating animals. Therefore, it is not recommended that lysine be given to these groups. Caution is needed when administering lysine to animals suffering from liver or kidney disease.

Lysine sold over the counter may contain propylene glycol, which may cause reactions in cats. It is important to confirm that over-the-counter lysine does not contain propylene glycol. Lysine may interact with certain other supplements and drugs, including calcium supplements, aminoglycoside medications, and steroids or other immune system suppressants. In humans, large doses of lysine may increase the toxicity of gentamicin, neomycin, and certain other antibiotics.

Lysine should not be used in animals with a known allergy or hypersensitivity to the drug. Overdose is rare and may cause upset stomach. Any known or suspected overdose should be reported to a veterinarian right away.


Lysine should be stored in a tightly sealed container, at room temperature, and out of the reach of children and animals. It should be kept in its original packaging.


Lysine is available over the counter in capsule, powder, and oral gel forms.

Dosing information for over-the-counter lysine products is usually for humans. A veterinarian should be consulted before dosing a dog or cat. A typical dose of lysine when treating adult cats infected with herpes virus is 500 mg twice daily.

Doses may vary in different species, when the drug is given by a different route or concurrently with other medications, and with regards to a patient's age, breed, and health status. A veterinarian's dosing instructions and/or those printed on the medication label should be followed closely.

If a dose of lysine is missed, it should be administered as soon as possible. If it is almost time for the next dose, the missed dose should be skipped and the regular dosing schedule should be resumed. It is important not to give animals two doses of lysine at once.

This information is for general reference only and should not be used for the diagnosis or treatment of any condition of your pet. It's intended as a general reference, this information may not include all possible uses, precautions, directions, reactions (including allergic), drug interactions, or withdrawal times. Always consult your local veterinarian and have your pet examined for any advice concerning the diagnosis and treatment of your pet, including which products and doses are most appropriate. Any trademarks are the property of their respective owners. VetDepot is not a pharmacy. All prescription products are dispensed by our Pharmacy Partner. Article last updated 2/2014.