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NOW Pets L-Lysine Immune System Support Cat Supplement, 8-oz jar

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At a Glance

  • Gluten Free
  • Immune Support
  • Eye Care
  • All Lifestages
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About This Item

Details

  • Created specifically for cats, this supplement helps support your buddy’s immune system, respiratory function, and eye health.
  • Made of pure L-lysine powder and free from any fillers.
  • Ideal for multi-cat households and for use when boarding.
  • Made with the same excellent-quality standards that NOW’s human supplements are made with.
  • Packaged in the USA by a family- and employee-owned company for a product you can feel good about.

Ingredient Information

Instructions

FAQ

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Questions & Answers

20 Customer Questions

Will this harm my cats if I feed it to them more then two times a week?

Answer by Chewy • Mar 19, 2022
Results from two clinical trials with cats suggest that excess dietary lysine may have an enhancing effect on FHV-1 replication, so some caution is suggested in supplementing. This newer evidence recently led NOW Pets' veterinarian formulator to recommend lowering the serving frequency, which they changed on their label over 8 months ago. One suggestion would be to pick specific days - for example, Wednesday and Sunday - to add the supplement. If you have any further questions please discuss with your vet.

How many servings does this jar have?

Answer by Chewy • Sep 10, 2022
NOW L-Lysine for Cats has a varying number of servings, depending upon weight. For cats up to 5 3/4 pounds, give 1/16 teaspoon twice weekly. For cats over 6 pounds, give 1/8 teaspoon twice weekly. Using a 1/8 tsp (276 MG) serving, divided into the total weight of 226.8g = 821 servings. If giving to a smaller cat (1/16 tsp) it would have twice as many servings. If using for one cat, twice weekly, as suggested, one bottle would last for years.

How long until l-lysine starts to suppress and alleviate any symptoms a cat may be experiencing?

Answer by Chewy • Jun 11, 2020
NOW Pets L-Lysine Immune System Support Cat Supplement supports a healthy immune system. There is no time frame in supporting the immune system.

Can you put the powder on dry food?

Answer by Chewy • Mar 24, 2018
This supplement should be administered during or after the animal has eaten to reduce the incidence of gastrointestinal upset. It can be added to their dry or wet food.
Reviews
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4.5
Rated 4.5 out of 5 stars
574 Ratings
Terms & Conditions

Customers Mention

Chewy identifies key considerations with the help of artificial intelligence and our veterinarians.

Ease of Use

77% Positive

Effectiveness

83% Positive

Ingredients

85% Positive

Long-Term Benefits

84% Positive

257 Customer Reviews

Rated 5 out of 5 stars
By Rose on Jan 25, 2026

So easy to give to a cat

OMG I am not big on doing reviews. My cat has a chronic respiratory infection. She had it for years. I just keep getting antibiotic shots for her. Recently I

OMG I am not big on doing reviews. My cat has a chronic respiratory infection. She had it for years. I just keep getting antibiotic shots for her. Recently I had to bring her to a different vet. Dottie was given the antibiotic shot. I was reading through the doctors notes and she recommended L-Lysine. I thought let me go on the Chewy site and see what I find. Chewy listed all the different products they carried and how they are different, gel, powder, flavored. I picked this Now Pets. Powder, no flavor, either 1/16 or 1/8 of a teaspoon according to weight twice a week. Wow, it can't get any easier. I noticed a change pretty quickly but as time went on Dottie was improving dramatically. She still sneezes but not as often or as bad as before. I would say a 90% improvement. The bottle states immune system support so I also give it to my other cat and to the ferals outside.

Rated 5 out of 5 stars
By Holly on Oct 13, 2025

Finally! One they would take!

I have tried the chews and turkey flavored drops, chews being a massive failure for both our kitten and grown kitty, drops only being accepted by the kitten slightly

I have tried the chews and turkey flavored drops, chews being a massive failure for both our kitten and grown kitty, drops only being accepted by the kitten slightly when mixed. But I sprinkled this in their food and neither could tell it was there. My older cat licked it right off the mixing spoon. I would give a 10 if it was designed to give more frequent like the others, but 3rd try was a charm. Don’t waste your money and time attempting to get them to take the others, it sucks feeling like a failure especially when you are trying to help your sick babies I 110percent recommend buying this one first and foremost.

Rated 5 out of 5 stars
By Catherine on Jan 25, 2026

Great for an FIV+ senior cat!

I took in an FIV+ senior cat about six months ago and started him on this when he was having issues gaining weight. I give him one scoop mixed in with his wet food

I took in an FIV+ senior cat about six months ago and started him on this when he was having issues gaining weight. I give him one scoop mixed in with his wet food each Sunday and Wednesday. It definitely seems to be helping! He's been gaining weight consistently over the past couple of months, he's gotten stronger, he looks much better, and isn't having health issues anymore. I can't attribute all that entirely to the lysine, but I think it definitely helped. This is a huge jar that will probably last the rest of his life, and when he's gone I'll probably start using it with my other cat because by then she'll be a senior too. I definitely recommend this for anyone with an FIV+ cat or a cat who is failing to thrive!

Rated 5 out of 5 stars
By Kelsey on Mar 31, 2026

Cured my cat’s alopecia!

I bought this for one of my cats who was sneezing every day and it completely stopped her sneezing, but I also gave it to my other cat who has been over grooming

I bought this for one of my cats who was sneezing every day and it completely stopped her sneezing, but I also gave it to my other cat who has been over grooming her belly and ankles for years. After around 1 month of consistently taking this supplement, her hair has started growing back!

Rated 5 out of 5 stars
By Sharon on Feb 13, 2026

It actually works!

I have been using Llysine products on 2 of my feline herpes cats for years . Sometimes it works IF you give large amounts. Then they don’t like the taste or texture

I have been using Llysine products on 2 of my feline herpes cats for years . Sometimes it works IF you give large amounts. Then they don’t like the taste or texture so they don’t want to eat. With NOW it only took a very small amount and they liked it ! Long story short no more meal time fuss, their eyes look great and it saves me a lot of money! I am one happy Kitty Mommy.

Rated 2 out of 5 stars
By Tomek on Apr 8, 2025

Not sure how I feel about this product (read papers)

My review is for this product, because I bought this product. Because they market towards cats, I feel justified in dinging them for the overall issue with L-Lysine

My review is for this product, because I bought this product. Because they market towards cats, I feel justified in dinging them for the overall issue with L-Lysine supplemants. They do not have data to support their safe usage in cats. The data that exists is only marginal benefits for humans. But cats have a different body and process argine and lysine differently. I did not feel safe giving this to my cat, and I feel like it is a net-negative to be offering it for sale. Please lookup whether L-Lysine is helpful for cats. Also, look up whether it is safe for cats. I believe there are two risks (1) Product purity. And frankly I would sooner buy L-lysine for humans than for pets, if that is my concern. (2) L-Lysine is genuinely not good for a cat, it seems. For many it doesn't hurt them, but they are likely to actually be recovering slower because it also does not benefit their immune system.

Rated 5 out of 5 stars
By Cherimo0n on Mar 22, 2021

Purrrfect!!!

Huge life saver for my 6 year old kitty who was diagnosed with feline herpes. He has been taking it for almost a month now and he's a completely different cat

Huge life saver for my 6 year old kitty who was diagnosed with feline herpes. He has been taking it for almost a month now and he's a completely different cat. Since his eyes were so bad I'd have to constantly wipe them, he would literally cower everytime I got near him, it broken my heart.. now he actually lays with me and purrs. forever grateful for this supplement and chewy for the fast delivery

Rated 4 out of 5 stars
By Kim on Aug 5, 2023

Dissolves well in wet food and cats don't seem to notice it

Like the title says, dissolves well when mixed with pate-style wet food, and our two kitties don't seem to notice it. However, the instructions for dosing are mislabeled

Like the title says, dissolves well when mixed with pate-style wet food, and our two kitties don't seem to notice it. However, the instructions for dosing are mislabeled on the container I received. I knew it should be twice daily instead of weekly because I've used numerous other lysine brands in the past, but this would have been very misleading for someone just starting their cat(s) on lysine.

Rated 2 out of 5 stars
By Dawn on Jun 21, 2025

Doesn’t seem to work as good as my human lysine crushed

I’ve used human L-Lysine in the past for kittens with herpes problems and it worked great, most noticeably solving their runny eyes. The two cats I’m using it with

I’ve used human L-Lysine in the past for kittens with herpes problems and it worked great, most noticeably solving their runny eyes. The two cats I’m using it with now are feral and had runny eyes and I was worried about their immune systems as well, but they could not be touched so I was using crushed human L-Lysine supplements crushed and mixed in their food. It has worked. I got this one for cats and have had to adjust the dosage because it doesn’t seem to work as well. I’ll keep using it to give it time, but if it doesn’t work and their eyes get worse, I’ll switch back to human crushed L-Lysine.

Rated 5 out of 5 stars
By Julie on Jan 13, 2021

Herpes baby

My little edgar has to have lysine everyday. The treats, he will eat for a couple of days then he refuses them. Even crushed in his wet food. Terd, lol. This

My little edgar has to have lysine everyday. The treats, he will eat for a couple of days then he refuses them. Even crushed in his wet food. Terd, lol. This powder, more like granules, is perfect. I just mix it in his wet food and he has no idea. He is doing excellent on it. His eyes look great and I haven't heard him sneeze or cough!!!!! Loving this!!!!