What is L-Lysine used for?

L-Lysine is indicated for: Feline herpesvirus-1 (FHV-1) management.

Which species have cited L-Lysine dosing data?

L-Lysine dosing in the ExoticRx formulary covers 1 species: Cat (Domestic).

Is L-Lysine a controlled substance?

L-Lysine is not federally scheduled in the US. Controlled-drug status differs by country — verify your local rules.

L-Lysine

US brand names:Enisyl-F, Viralys

Calculate dosage

Sourced from published veterinary references. Awaiting credentialed clinical reviewer — our editorial process.

L-Lysine is dosed at 250–500 mg/cat PO q12-24h in cats, per Rees TM, Lubinski JL. Oral supplementation with L-lysine did not prevent upper respiratory infection in a shelter population of cats. J Feline Med Surg. 2008;10(5):510-513. doi:10.1016/j.jfms.2008.03.004; Maggs DJ. Antiviral Therapy for Feline Herpesvirus Infections. Veterinary Clinics of North America-Small Animal Practice. 2010;40(6):1055-+. doi:10.1016/j.cvsm.2010.07.010 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.815 (2026-08-01).. Verify against current literature before clinical use.

Drug Class

Antiviral

Routes

Indications

Feline herpesvirus-1 (FHV-1) management

Mechanism of Action

Competes with arginine for absorption and incorporation. Theoretically suppresses herpesvirus replication by reducing arginine availability needed for viral protein synthesis.

Side effects & warnings

Efficacy debated in recent studies. Generally very safe. May cause GI upset at high doses. Commonly used for FHV-1 in cats despite limited evidence.

Species with L-Lysine dosing data (1 dose rule)

Cat (Domestic)

Species references:All Cat (Domestic) drugs

Evidence levels across 1 dose rule

Weak×1

Each ExoticRx dose rule is graded by the strength of its primary evidence — see the editorial process.

Backed by a published source

· Rees TM, Lubinski JL. Oral supplementation with L-lysine did not prevent upper respiratory infection in a shelter population of cats. J Feline Med Surg. 2008;10(5):510-513. doi:10.1016/j.jfms.2008.03.004; Maggs DJ. Antiviral Therapy for Feline Herpesvirus Infections. Veterinary Clinics of North America-Small Animal Practice. 2010;40(6):1055-+. doi:10.1016/j.cvsm.2010.07.010 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.815 (2026-08-01).

Sample dosing (1 of 1 cited rule)

A dog/cat sample is shown here. Cited dosing for all 1 species — reptiles, birds, pocket pets, livestock, and equine — is free on the per-species pages above. Pro adds the weight-based calculator for every species.

Species	Route	Dose	Frequency	Evidence	Source
Cat (Domestic)	PO	250–500 mg/cat	q12-24h	Weak	Rees TM, Lubinski JL. Oral supplementation with L-lysine did not prevent upper respiratory infection in a shelter population of cats. J Feline Med Surg. 2008;10(5):510-513. doi:10.1016/j.jfms.2008.03.004; Maggs DJ. Antiviral Therapy for Feline Herpesvirus Infections. Veterinary Clinics of North America-Small Animal Practice. 2010;40(6):1055-+. doi:10.1016/j.cvsm.2010.07.010 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.815 (2026-08-01).

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