Taurine vs Lysine for Cats: What Each One Does and Which Your Cat Needs

Taurine vs lysine for cats is not really a contest, because the two do different jobs. Taurine is a nutrient every cat must eat, for the eyes and heart. Lysine is an amino acid supplement that owners often try for herpesvirus signs like sneezing and runny eyes. The evidence behind each is very different too.

This guide compares them side by side. It covers what each does, what the research says, and when your vet might suggest one, both or neither.

For deeper reading, see our guides to taurine for cats and L-lysine for cats.

Taurine vs Lysine for Cats: Side by Side

First, the big picture. The table below sums up the key differences in taurine vs lysine for cats.

In short, taurine fills a nutrient need. Lysine, on the other hand, is an add-on with weak evidence. So the two are not swaps for each other.

What Taurine Does for Cats

In the taurine vs lysine for cats debate, taurine is the one cats cannot do without. VCA Animal Hospitals explains that cats have a limited ability to make it. Also, taurine is found only in animal protein, and cats do not store much of it.

• Eyes: a shortage causes feline central retinal degeneration.
• Heart: a shortage causes dilated cardiomyopathy (DCM).
• Digestion: taurine is part of bile salts.
• Reproduction: low levels can cause small litters and slow kitten growth.

The landmark 1987 Pion study in Science linked heart muscle failure to low blood taurine in cats fed commercial foods. Oral taurine went along with heart function returning to normal. As a result, makers raised taurine levels in cat food.

Today, AAFCO requires at least 0.10% taurine in dry food and 0.20% in canned food, on a dry matter basis. That is why VCA says a healthy cat on a high-quality complete food does not need a supplement.

Taurine vs lysine for cats: daily taurine needs

A 1991 Waltham study found cats need at least 39 mg of taurine per kg of body weight a day on canned food. On dry food, they need at least 19 mg per kg. Our taurine dosage guide explains those numbers.

What Lysine Does for Cats

In contrast, lysine is an amino acid found in protein. As a supplement, VCA notes it is used for clinical signs of feline herpesvirus, such as sneezing and eye problems. The idea was that lysine might block arginine, which the virus needs.

Meanwhile, herpesvirus is very common. Cornell says up to 97% of cats are exposed to it. Up to 80% stay infected for life, and up to 45% shed the virus again, usually under stress. That is why so many owners look into lysine.

However, the theory has not held up well. A 2015 systematic review by Bol and Bunnik found that lysine does not block arginine in cats. It also found lysine has no antiviral properties. Our guide to L-lysine for cats covers this in depth.

Taurine vs Lysine for Cats: What the Evidence Says

This is where the gap between taurine vs lysine for cats is widest. Taurine has clear evidence of need. Lysine, by contrast, has mixed and mostly negative results.

Taurine vs lysine for cats: lysine studies at a glance

• Stiles, 2002: in a study of 8 healthy cats, 500 mg twice daily led to less severe conjunctivitis than placebo after virus exposure. Virus levels were not different.
• Maggs, 2003: in 14 cats with latent infection, 400 mg once daily reduced shedding after rehousing, but not after steroid-triggered flare-ups.
• Rees and Lubinski, 2008: in a shelter study of 291 cats, lysine had no effect on respiratory infection or conjunctivitis.
• Drazenovich, 2009: in a study of 261 shelter cats, treated cats had more moderate to severe disease by week 4.

The 2015 review weighed these and more. It found no evidence that lysine prevents or treats herpesvirus, and it recommended stopping lysine supplementation. Similarly, Cornell notes that several studies suggest lysine is not effective and may make signs worse.

Why some vets still use lysine

Still, the picture is not all one-sided. The same review found over 90% of vets in cat hospitals recommended lysine. Also, an MSPCA-Angell ophthalmologist still offers it to cats that tolerate it. However, they advise skipping it if giving it causes stress or poor appetite.

Taurine vs Lysine for Cats: Which Cats Might Need Each?

Because they do different jobs, the answer to taurine vs lysine for cats depends on your cat's diet and health.

Taurine vs lysine for cats: who might need extra taurine

• Homemade or raw diets
• Vegetarian food
• Dog food, which VCA says lacks enough taurine for a cat
• Heart or eye disease, as part of a vet's treatment

In addition, Merck notes that taurine-related DCM is still seen in cats fed vegetarian, baby or home-cooked food.

Cats a vet might offer lysine

• Cats with herpesvirus flare-ups, if the vet still uses it
• Cats that accept it easily, without stress

Besides lysine, your vet has other tools for herpesvirus. Cornell lists antiviral drugs among treatments. Because of that, a cat with severe eye signs should see the vet promptly, rather than wait to see if a supplement helps. In addition, the AAHA/AAFP vaccination guidelines list the herpesvirus and calicivirus vaccines as core for pet cats.

So in the choice of taurine vs lysine for cats, many healthy cats need neither as a supplement. Our guide to why your cat is sneezing helps you sort out respiratory signs first.

Can You Give Taurine and Lysine Together?

Yes, the two can be given at the same time if your vet agrees. They work in different ways, and we know of no reason they cannot share a meal. Still, VCA advises caution when lysine is given with arginine or oral calcium supplements.

• Ask your vet first. Make sure your cat needs each one.
• Start one at a time. That way, you can tell which one causes any upset.
• Keep amounts separate. Use each label's serving or your vet's amount.
• List every product. Tell your vet about all supplements and medicines.

In other words, taurine vs lysine for cats is not an either-or choice. It is two separate questions, each with its own answer.

Taurine vs lysine for cats in a multi-cat home

Homes with several cats need a little more care. For example, one cat may need taurine for a homemade diet, while another gets lysine for herpes flare-ups. So label each bowl, and feed the cats apart at supplement meals. Also, keep a simple chart on the fridge. That way, everyone in the house knows which cat gets which product. In short, taurine vs lysine for cats in a busy home is mostly about clear routines.

Myths About Taurine vs Lysine for Cats

Online advice often blurs the two. So here are four common myths, and what the sources actually say.

• "Lysine is a must for every cat." In fact, the 2015 review recommended stopping lysine supplementation, since it found no proof it works.
• "Taurine and lysine do the same thing." They do not. Taurine supports eyes and heart, while lysine was aimed at herpesvirus.
• "Lysine lowers arginine and harms cats." Actually, the review found lysine does not block arginine in cats.
• "Indoor cats need extra taurine." Not because they live indoors. Instead, diet decides it.

In short, taurine vs lysine for cats comes down to two separate questions. First, is the diet short on taurine? Second, does your vet still use lysine for herpes signs? Answer each one on its own.

Taurine vs lysine for cats: cost and value

Price is another point owners weigh in taurine vs lysine for cats. However, value depends on need. A supplement your cat does not need costs money and adds nothing. So, for taurine vs lysine for cats, ask whether each one solves a real problem first. Then compare the cost per serving of clearly labeled products. Also, check the mg per serving, since scoops differ between brands.

For example, a cat on homemade food may get real value from taurine. Meanwhile, a healthy cat on complete food may need neither. That is why taurine vs lysine for cats is a vet question before it is a shopping question.

Taurine vs Lysine for Cats: Forms and Daily Routine

Similarly, both come as powders, capsules and other forms. VCA lists lysine as a powder, crushed tablet, chewable tablet or paste. Taurine is sold over the counter in similar forms.

For powders, first mix each serving into a small portion of wet food. Then serve the rest once your cat eats it. VCA suggests giving lysine with a small amount of food, ideally at the same time each day.

See our guides on how to add taurine to cat food and lysine dosage for cats for more detail.

Taurine vs Lysine for Cats: Safety Compared

Overall, both have good safety records at normal amounts. Even so, there are differences worth knowing.

• Taurine: VCA calls supplementation relatively safe, with no reports of problems from excess dietary taurine in cats. AAFCO sets no maximum, though, so follow the label or your vet.
• Lysine: VCA lists diarrhea as a side effect. It also advises caution in pregnant or nursing cats.
• Lysine and illness: some studies, such as the 2009 shelter trial, found more severe disease in treated cats.

Also, VCA notes that the FDA does not review non-drug supplements for safety or effectiveness before sale. So choose clearly labeled products for either one. Our guides on is taurine safe for cats and lysine side effects go deeper.

Questions to Ask Your Vet

Bring your cat's food labels and a list of current supplements.

• Does my cat's diet already supply enough taurine?
• Do you still recommend lysine for my cat's herpesvirus signs, given the research?
• Would an antiviral drug or a vaccine booster help more?
• If I give taurine vs lysine for cats, or both, what amount of each?
• Are there any medicines or supplements I should not combine?

In short, in taurine vs lysine for cats, taurine is about meeting a nutrient need, while lysine is about managing a virus with weak evidence. Your vet can help you match each one to your cat. Our taurine FAQ has more quick answers.

Related guides: Do cats need taurine supplements? · How long to give cat lysine · Best taurine supplement for cats

More taurine guides: Taurine vs L-carnitine for cats

Key Terms Explained

• Taurine: a nutrient cats must eat every day; in taurine vs lysine for cats, it is the essential one.
• L-lysine: an amino acid sold as a supplement, mainly used for cats with feline herpesvirus signs.
• Feline herpesvirus (FHV-1): a common virus that causes sneezing, eye discharge and conjunctivitis in cats.
• Arginine: an amino acid cats cannot make enough of; lysine was once thought to block it.
• Dilated cardiomyopathy (DCM): a heart muscle disease that low taurine can cause in cats.

This article is for general education and is not veterinary advice. These statements have not been evaluated by the Food and Drug Administration. Kittysum products are not intended to diagnose, treat, cure or prevent any disease.