Best Cat L-Lysine Supplements (2026) – Top 10 Reviewed

L-lysine is one of the most widely recommended supplements for cats, especially those dealing with feline herpesvirus, upper respiratory infections, or immune challenges. This essential amino acid supports immune function, respiratory health, and eye comfort — and since cats can’t produce it on their own, supplementation can make a real difference. We’ve reviewed the best L-lysine supplements for cats to help you choose the right product for your feline companion.

Our Top Picks at a Glance

• Best Overall: Strawfield Pets L-Lysine Immune Support – High-dose powder with natural chicken liver flavor
• Best Value: Pet Naturals Lysine for Cats – Affordable chews with 250mg lysine per treat
• Best Premium: Vetoquinol Viralys L-Lysine Powder – Trusted veterinary brand with 500mg per scoop

Quick Comparison

Product	Key Ingredients	Form	Servings	Best For
Strawfield Pets L-Lysine Immune Support	L-Lysine 900mg/scoop	Granules	200g container	Overall immune support
Pet Naturals Lysine for Cats	L-Lysine 250mg	Soft Chews	60	Budget-friendly daily support
Vetoquinol Viralys L-Lysine Powder	L-Lysine HCl 500mg/scoop	Powder	100g container	High-dose veterinary formula
SANTKOL L-Lysine Liquid Drops	L-Lysine HCl, Astragalus, Vitamins	Liquid	60ml	Liquid format for picky cats
Balanced Breed L-Lysine Soft Chews	L-Lysine, Krill Oil, Vitamin B12, Folic Acid	Soft Chews	Varies	Multi-benefit immune chews
PRN Duralactin Feline L-Lysine Paste	L-Lysine 250mg, Microlactin, Omegas	Paste	32.5ml tube	Joint and respiratory dual support
NOW Pets L-Lysine Powder	100% L-Lysine HCl	Powder	8oz container	Pure lysine, best price per dose
VetriScience Lysine Immunity Health Chews	L-Lysine 250mg, DMG	Chews	90	Enhanced immune response
Felisyl L-Lysine Gel	L-Lysine	Gel	5oz tube	Easy-to-administer salmon flavor
Tomlyn Immune Support L-Lysine Chews	L-Lysine	Chews	30	Fish-flavored daily chews

1. Strawfield Pets L-Lysine Immune Support – Best Overall

With 900mg of L-lysine per scoop and a natural chicken liver flavor, Strawfield Pets delivers the most potent and palatable powder supplement available.

This granulated supplement provides double the lysine per scoop compared to most competitors. The chicken liver powder makes it easy to mix into your cat’s daily meal without detection, and the granule form blends smoothly into wet food, canned food, or even raw diets. It’s designed to support cats dealing with feline herpes virus symptoms including sneezing, congestion, runny nose, and watery eyes.

What We Like

• Highest lysine dose per scoop at 900mg — double most competitors
• Natural chicken liver flavor that cats love
• Lab-tested for safety, manufactured in a cGMP-certified USA facility

What Could Be Better

• Granule format may be noticed by extremely picky eaters
• Large container may not be needed for single-cat households

Bottom Line: Strawfield Pets offers the most potent and well-received lysine powder on the market, making it the top choice for cats needing robust immune support.

2. Pet Naturals Lysine for Cats – Best Value

These affordable, fish-shaped chicken liver chews make daily lysine supplementation easy and budget-friendly.

Each soft chew contains 250mg of L-lysine in a tasty chicken liver flavor that most cats eagerly accept as a treat. The fun fish shape and soft texture make them easy to feed — just give 1-2 chews per day. They’re free from wheat, corn, and artificial flavors, and a single bag provides up to a 60-day supply, making them ideal for multi-cat households watching their budget.

What We Like

• Excellent price point with up to 60-day supply
• Cats love the chicken liver flavor and fish shape
• No wheat, corn, or artificial ingredients

What Could Be Better

• Contains soy and oat flour — not suitable for cats with those sensitivities
• 250mg per chew is a moderate dose

Bottom Line: Pet Naturals is the smartest choice for cat owners who want effective lysine support without spending a fortune.

3. Vetoquinol Viralys L-Lysine Powder – Best Premium

This veterinary-trusted brand delivers 500mg of L-lysine per scoop in a highly palatable fish-poultry flavored powder.

Vetoquinol is a name veterinarians know and trust. Viralys provides 500mg of L-lysine hydrochloride per scoop and is formulated specifically for cats and kittens of all ages and sizes. The powder has a fish-poultry flavor that most cats find appealing when mixed into food. Vetoquinol manufactures Viralys in North America under strict pharmaceutical guidelines and is a proud NASC member.

What We Like

• Established veterinary brand with NASC membership
• 500mg per scoop provides a strong therapeutic dose
• Also available as gel, paste, and chew formats

What Could Be Better

• Powder may settle to the bottom of wet food
• Fish flavor may not appeal to every cat

Bottom Line: When your veterinarian recommends lysine, Viralys is often the brand they have in mind — trusted, effective, and backed by pharmaceutical-grade manufacturing.

4. SANTKOL L-Lysine Liquid Drops

These chicken-flavored liquid drops combine L-lysine with traditional herbal ingredients for a unique approach to feline immune support.

SANTKOL’s liquid formula includes L-lysine HCl alongside astragalus for vitality, codonopsis for energy, atractylodes macrocephala for digestive health, and burdock seed for skin and coat nourishment. The roast chicken flavor makes it appealing to even picky cats, and the liquid format can be given directly, mixed with food, water, or milk. It’s grain-free, alcohol-free, and gluten-free.

What We Like

• Unique blend of lysine with traditional herbal support ingredients
• Liquid format is versatile — multiple ways to administer
• Free from grains, alcohol, gluten, and harmful chemicals

What Could Be Better

• Herbal ingredients may not appeal to all cat owners
• 60ml bottle is relatively small

Bottom Line: SANTKOL offers a distinctive lysine supplement that combines amino acid support with herbal ingredients for cats who need a comprehensive wellness boost.

5. Balanced Breed L-Lysine Soft Chews

These vet-pharmacist approved chews combine L-lysine with krill oil, vitamin B12, and folic acid for multi-system immune support.

Balanced Breed takes a multivitamin approach to lysine supplementation, pairing L-lysine with krill oil for omega-3 fatty acids, vitamin B12 for energy, and folic acid for cellular health. The soft chews are made in the USA, non-GMO, and third-party tested. They’re designed to support respiratory health, allergy relief, and overall immune function in one convenient daily treat.

What We Like

• Multi-ingredient formula provides broader health support
• Vet-pharmacist approved with third-party testing
• Non-GMO, chemical-free, and made in the USA

What Could Be Better

• Recommended for adult cats — consult vet for kittens under 12 months
• Natural ingredients may cause texture and appearance variation between batches

Bottom Line: Balanced Breed’s multi-ingredient approach makes these chews ideal for cat owners who want lysine plus additional immune-boosting nutrients in one supplement.

6. PRN Duralactin Feline L-Lysine Paste

This unique paste combines L-lysine with Microlactin, a patented milk protein that helps manage chronic soreness and inflammation.

PRN Pharmacal’s Duralactin paste delivers 250mg of L-lysine alongside 200mg of Microlactin per half-teaspoon dose. Microlactin is a dried milk protein concentrate derived from hyperimmunized cows that has been shown to help manage chronic soreness. The paste also includes omega-3 and omega-6 fatty acids. The chicken-flavored, dial-dose syringe makes administration simple and accurate.

What We Like

• Patented Microlactin provides unique anti-inflammatory benefits
• Dial-dose syringe for precise, mess-free administration
• Dual support for respiratory health and chronic soreness

What Could Be Better

• Contains sucrose and malt syrup as inactive ingredients
• Smaller tube size requires more frequent repurchasing

Bottom Line: Duralactin is the ideal choice for cats dealing with both respiratory issues and chronic joint or tissue soreness.

7. NOW Pets L-Lysine Powder

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This pure, single-ingredient lysine powder offers the best value per dose and carries the NASC quality seal.

NOW Pets keeps it simple with 100% L-lysine hydrochloride — no fillers, no flavorings, no extras. This makes it the most affordable lysine supplement per serving and the best option for cat owners who want pure lysine without additional ingredients. The 8oz container provides a generous supply, and the NASC certification ensures manufacturing quality and safety.

What We Like

• Lowest cost per dose of any lysine supplement
• NASC quality seal certification
• Large 8oz container lasts a long time

What Could Be Better

• Unflavored formula may be detected by picky cats
• Granular texture can be visible on food

Bottom Line: If you want pure, affordable lysine without the extras, NOW Pets delivers the best bang for your buck with NASC-certified quality.

8. VetriScience Lysine Immunity Health Chews

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These chicken liver-flavored chews pair 250mg of L-lysine with DMG to significantly boost immune response.

VetriScience’s formula stands out by including DMG (dimethylglycine), which has been shown to significantly increase immune response in animals. The hydrolyzed protein base makes these chews suitable for cats with dietary sensitivities. Each chew delivers 250mg of lysine, and the 90-count bottle provides a generous 3-month supply at the standard daily dose.

What We Like

• DMG addition provides enhanced immune-boosting benefits
• Hydrolyzed protein suitable for sensitive cats
• 90-count bottle offers excellent long-term value

What Could Be Better

• Some cats may not find the texture appealing
• Chicken liver flavor can have a strong smell

Bottom Line: VetriScience’s DMG-enhanced formula is the top choice for cat owners seeking maximum immune support beyond basic lysine supplementation.

9. Felisyl L-Lysine Gel for Cats

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This salmon-flavored gel makes lysine administration a breeze for cats who refuse powders, chews, and liquids.

Felisyl’s gel format offers another option for difficult-to-supplement cats. The salmon flavor is designed to be irresistible to felines, and the gel can be squeezed directly into your cat’s mouth, applied to their paw for self-licking, or mixed into food. The 5oz tube provides a generous supply and is made in the USA with quality ingredients that support immune, respiratory, and eye health.

What We Like

• Salmon flavor is highly appealing to most cats
• Multiple administration methods for flexible use
• Made in the USA with quality assurance

What Could Be Better

• Gel can be messy if your cat shakes their head during oral dosing
• Tube packaging can be difficult to squeeze when nearly empty

Bottom Line: Felisyl’s salmon-flavored gel is perfect for cat owners who’ve struggled with other lysine formats and need an alternative their cat will accept.

10. Tomlyn Immune Support L-Lysine Chews

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These fish-flavored daily chews from a trusted pet health brand provide simple, effective lysine supplementation.

Tomlyn is a well-known name in pet health products, and their L-lysine chews deliver straightforward immune support in a convenient daily treat format. The fish flavor appeals to most cats, and the chews are appropriately sized for felines. While the 30-count package is smaller than some alternatives, it provides a full month of daily support and is a good option for trying lysine supplementation before committing to a larger supply.

What We Like

• Trusted pet health brand with established reputation
• Fish flavor that cats enjoy
• Good starter option before committing to larger packages

What Could Be Better

• Only 30 chews per package — smaller supply than competitors
• Higher per-chew cost compared to larger packages

Bottom Line: Tomlyn’s chews are a reliable option from a trusted brand, especially if you want to test lysine supplementation before buying in bulk.

How to Choose the Best L-Lysine Supplement for Your Cat

The most important factor in choosing a lysine supplement is finding one your cat will actually take. Lysine supplements come in powders, granules, liquids, gels, pastes, and chews — and what works for one cat may be rejected by another. If your cat eats wet food, powders and liquids that mix into their meal are often the easiest to administer. For dry food-only cats, chews or gel supplements may be better options.

Dosage matters significantly with lysine. Most veterinarians recommend 250-500mg of L-lysine daily for adult cats, with some suggesting up to 1,000mg per day split into two doses for cats actively fighting herpesvirus symptoms. Check the amount of lysine per serving and calculate how many servings you’ll need to reach your vet’s recommended dose.

Consider whether you want a pure lysine supplement or one with additional immune-supporting ingredients. Products that include omega-3 fatty acids, DMG, probiotics, or vitamins may provide broader health benefits. However, if your cat is on other medications or supplements, a pure lysine formula reduces the risk of ingredient overlap or interactions.

Quality and safety certifications should factor into your decision. Look for products carrying the NASC quality seal, manufactured in cGMP-compliant facilities, and produced in the USA. These indicators provide assurance that the supplement contains what the label claims and has been produced under strict safety standards.

Cost per serving is worth calculating, as there can be significant price differences between brands. A large container of pure lysine powder is typically the most economical option, while flavored chews and specialty gels tend to cost more per dose. For multi-cat households, buying in bulk can save substantial money over time.

Benefits of L-Lysine Supplements for Cats

L-lysine is an essential amino acid that cats cannot produce on their own — they must obtain it from their diet or through supplementation. Lysine plays a critical role in the production of antibodies, hormones, and enzymes, making it fundamental to a strong immune system. Supplemental lysine can help support your cat’s natural defenses against common feline health challenges.

One of the primary uses of lysine supplementation is managing symptoms associated with feline herpesvirus (FHV-1). Lysine competes with L-arginine, an amino acid that the herpesvirus needs to replicate. By supplementing with lysine, you can help reduce the severity and frequency of herpesvirus flare-ups, including symptoms like sneezing, nasal discharge, and conjunctivitis.

Lysine also supports respiratory and eye health more broadly. Cats prone to upper respiratory infections — including shelter cats, kittens, and cats in multi-cat households — can benefit from daily lysine supplementation to help keep their respiratory system functioning properly and maintain normal eye health and comfort.

Beyond immune support, lysine plays a role in healthy growth and development by supporting collagen production. Collagen is essential for skin, coat, and connective tissue health. This makes lysine supplementation beneficial not just for sick cats, but as a general wellness support for cats of all ages.

Frequently Asked Questions

Is L-lysine safe for kittens?

Yes, most lysine supplements are safe for kittens, typically starting around 4-6 months of age. Kittens usually receive a lower dose — often half the adult dose. Always check the product label for age recommendations and consult your veterinarian before starting any supplement for a young kitten.

Can I give my cat L-lysine every day?

Yes, lysine supplements are generally safe for daily long-term use with no known side effects when given according to label directions. Many veterinarians recommend continuous daily supplementation for cats with chronic herpesvirus or recurring upper respiratory issues.

How much L-lysine should I give my cat?

The typical recommended dose is 250-500mg once or twice daily for adult cats. During active flare-ups, some veterinarians may recommend up to 1,000mg per day split into two doses. Always follow your veterinarian’s specific dosing recommendations for your cat’s situation.

Does L-lysine actually work for cats with herpes?

Many veterinarians and cat owners report positive results with lysine supplementation for managing herpesvirus symptoms. While some studies have shown mixed results, lysine remains one of the most commonly recommended supplements for feline herpesvirus management due to its safety profile and positive anecdotal evidence.

Can I use human L-lysine supplements for my cat?

While the active ingredient is the same, human lysine supplements may contain fillers, coatings, or dosages inappropriate for cats. Cat-specific supplements are formulated with feline-friendly flavors, appropriate dosages, and safe inactive ingredients. It’s best to use a product made specifically for cats.

What’s the best time of day to give my cat lysine?

Lysine can be given at any time of day, though many cat owners find it easiest to administer at mealtimes when they can mix it into food. If your cat’s dose is split into two daily servings, spacing them 12 hours apart (morning and evening meals) provides the most consistent levels throughout the day.

Will lysine help my cat’s sneezing and runny nose?

If your cat’s sneezing and nasal discharge are related to feline herpesvirus or general immune challenges, lysine supplementation may help reduce the severity of these symptoms over time. However, sneezing and discharge can have many causes, so you should have your cat evaluated by a veterinarian to identify the underlying issue.

Can I give lysine to all the cats in my household?

Yes, lysine is safe for cats of all ages (typically 4 months and older) and is especially beneficial in multi-cat households where upper respiratory infections can spread easily. Many cat owners supplement all their cats as a preventive measure, particularly during stressful periods.

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