Probiotics for Cats: A Nonsense-Free Buyer’s Guide

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Hey there, radical cat parents. Welcome to our new and improved guide to probiotics for cats!

We’ve learned a lot since publishing our first article on probiotics for cats in 2017.

Since then, I’ve spent hours combing through customer reviews, discovered that a disturbing number of cat probiotic supplements have really bad grades on, read miles of threads on TheCatSite forums, and a few months ago, had an interview with Dr. Ryan Honaker, a microbiologist researching the cat and dog microbiome. This spring, we collected samples of Wessie and Forest’s poop and sent them off to a lab for microbiological analysis.

Now that I feel I have a better understanding of this crazy-complex world of bugs and charlatanry, I think I’m ready to update that article we published back in 2017.

I’ve done my best to gather everything we’ve learned about the feline microbiome and probiotics for cats and put it together in this comprehensive guide.

Hopefully, you find this a helpful resource that puts all—or at least most—of the information you need in place. It’s going to be long, so you’re encouraged to read a bit, bookmark it, and come back later. Use the quick navigation to jump from place to place.

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What are you going to get out of this article? 

You’ll first learn what probiotics are before we discuss whether or not they’re “natural” for cats and which cats can benefit from probiotic supplementation. After we’ve covered all of that background information, we’ll get into the buyer’s guide. 

In the buyer’s guide, you’ll learn how to choose a good probiotic product by looking at viability, reputation, and the types of strains the product contains. Finally, we’ve listed the probiotic supplements that, according to our knowledge of the market, are some of the best you can buy.

Let’s get into it!

What are probiotics?

Your cat’s not just a cat. He’s an ecosystem. 

Your cat’s body is the environment for a multi-billion-strong population of microscopic organisms. As they go about their business of eating and excreting and reproducing, these little organisms have a profound effect on the environment in which they live. 

We already knew that when yeasts hang out with bacteria in a bowl of flour and water, they make a sourdough starter. When bacteria hang out in a bowl of milk, they make yogurt. But it was only recently that we started to understand how the bacteria in the body transforms it into something new. 

Research on the effects of the microbiome on both animals and humans has found that this inner ecosystem has an impact on almost every aspect of life. 

Here are some examples of the effect the microbiome (and gut bacteria, specifically) has on people and other animals:

  • It’s a central part of digestion. Gut bacteria ferment fiber, which releases chemicals that aid the digestive process. 
  • Do you think you decide what you want to eat? It turns out that your microbiome may be making at least part of that decision for you. Researchers found that sterile insects craved yeast, while those with a diverse gut flora ate both yeast and sugar. If you’re craving chocolate, berries, or ice cream, that’s likely your gut microbiota telling you what they need. 
  • If you transfer gut bacteria from an “anxious” mouse into a calm mouse, the second mouse will start showing signs of anxiety
  • Sterile mice—carefully raised to never develop their own microflora—were found to have 60% less serotonin, popularly called the “happy chemical”. Low levels of serotonin are associated with sadness, obsessiveness, sleeplessness, and general psychological depression.
  • Gut bacteria may be connected to autism. It appears that people with autism have lower populations of the bacteria Bacteroides fragilis. When given to mice exhibiting autism-like behaviors, this bacteria seemed to reduce those symptoms. When mice were given 4-ethylphenylsulphate, a chemical that’s thought to be produced by gut bacteria, they started having more repetitive behaviors and symptoms of autism.
  • Gut bacteria is intertwined with the immune system to an extent that people don’t yet fully understand. More or less gut bacteria influences the body’s reaction to and tendency to develop various conditions, but again, these dynamics aren’t fully understood. 

There’s no doubt that the microbiome is vital, but probiotic supplementation is not yet a fully understood science. 

The theory behind probiotic supplementation is that by adding some more friendly microorganisms to the mix, we can amplify the benefits of the microbes already there. But it’s not that simple. 

Still in question are whether or not that works, when it works, and which types of microorganisms are a good fit for your cat’s gut. 

Are probiotics good for cats?

A few months ago, I had an interview with Dr. Ryan Honaker. Dr. Honaker is the Director of Microbiology at Nom Nom, where he’s responsible for studying the cat and dog microbiome, creating bacterial profiles of cat poop, and generally furthering our collective understanding of how the gut flora impact our lives.

One of the most powerful takeaways from that conversation happened when we were talking about the potential of this research. Ryan said, “we can’t see the bottom of what it is.”

He was talking about the massiveness of understanding the gut microbiome in general, but the potential power of probiotics alone is equally staggering and unknown. At this point, we don’t know very much about how probiotics impact people and the research on cats is scarce.

What we do know is this:

  • Probiotics definitely help cats with diarrhea and constipation.
  • Probiotics should support general digestive health.
  • They help to restore friendly bacteria after antibiotic treatment.
  • Probiotics may help cats with kidney disease.

What we don’t know is exactly which strains are best for cats. Instead, most of our understanding of the feline microbiome has been, up until recently, based on extrapolations from what we know about the human microbiome. Without knowing what’s supposed to be in your cat’s body and how it affects your cat’s health, we can’t create effective feline probiotic supplements.

That’s why the research Dr. Ryan Honaker is performing with Nom Nom is so valuable.  Want to help scientists understand the feline microbiome and help Nom Nom make better probiotics? 

Click here to learn more about the Nom Nom: INSIGHTS Microbiome Testing Kit.

How do you know if your cat needs probiotics?

Whether healthy or sick, any cat can benefit from probiotic supplementation. In fact, a diversity of probiotic bacteria is a natural part of the feline diet. By adding probiotics, we’re adding back what is lost during the processing of human-made diets. 

A cat’s natural diet contains both prebiotics in the form of what you could call animal fiber, those indigestible parts of an animal’s body. It also contains digestive enzymes from the little critter’s gut, beneficial yeasts, and bacteria also present in that little gut. 

So considering that there does seem to be a precedent for supplementing your cat’s diet with probiotics, you could think of them as an essential supplement just like taurine. Probiotics can also do great things for cats with certain health conditions. 

Probiotics for Cats with IBD

Irritable bowel disease or IBD is a complex, little-understood disease that causes constant nausea, chronic vomiting and diarrhea, and in many cases, years of confusion and stress for the person caring for their sick cat. Though the exact cause or causes of IBD aren’t known, gut bacteria seem to play a part. 

We know that a fecal transplant can help cats with IBD by introducing another animal’s bacteria into your cat’s gut. We also know that S boulardii yeast can stop diarrhea and reduce inflammation. 

Other probiotic strains and therapies are being explored for cats with IBD, but so far, we can only say that supporting a healthy gut microbial population can help. A combination of diet, supplements, and lifestyle work together to treat IBD.

Probiotics for Cats with Constipation

Gut bacteria and fermentation play an important role in helping the stool to retain water, a process that’s essential in preventing constipation. When bacteria ferment fiber, they release short-chain fatty acids, which help the stool retain water, plump up or soften, and, hopefully, pass out of the body. Generally, we give constipated cats fiber to feed the existing bacteria in their guts, but if the population is meager, there won’t be anyone there to eat that fiber. 

In theory, a probiotic supplement can help. The only problem is that we don’t know which probiotics are best for cats with constipation. 

Probiotics for Cats with Diarrhea

Saccharomyces Boulardii or S. boulardii is a non-colonizing yeast with a strong reputation for treating acute and chronic diarrhea. IBDKitties has an excellent guide to treating diarrhea with this supplement. 

Probiotics for Cats with Allergies

Probiotic supplementation may help your allergic cat, but it’s not an exact or well-understood science. We know that a combination of lactobacilli and bifidobacteria probiotics can help humans to deal with allergies. By influencing the way the immune system responds to perceived threats—like allergens—these probiotics can help to control symptoms of allergies. 

But the research on probiotics for allergies is limited and focuses on humans rather than cats, so it’s hard to say whether they are a promising therapy for allergic kitties.

Probiotics for Cats with Kidney Disease

Probiotics may be able to help cats with kidney disease by performing what’s called enteric dialysis. That’s when the bacteria in the gut take over part of the kidneys’ job, processing at least some of the waste product that failing kidneys no longer filter out of the body.

The leading probiotic for cats with kidney disease is called Azodyl. In theory, this supplement reduces the amount of nitrogen waste in the blood. Results are mixed, with some cats showing improvement and others not. Overall, Azodyl and other probiotics are not reliable treatments for kidney disease.

Probiotics for Cats on Antibiotics

If your cat has gone through a round of antibiotics, probiotic supplementation can help to repopulate the intestines with beneficial bacteria. When taken during antibiotic treatment, probiotics can reduce the risk of antibiotic-caused diarrhea.

How to Choose the Best Probiotics for Cats

The animal probiotics market is rife with charlatanry. 

Probiotics are the perfect product for exaggerated claims and inconsistent quality control. With such massive potential benefits and so little real understanding of what those benefits actually are and how to achieve them, probiotic peddlers can say almost anything about their products. Like other nutraceuticals, probiotics’ health claims don’t need to be backed by facts or testing.

Particularly for cats, considering how little the feline microbiome is currently understood, there are no regulatory standards for what a probiotic needs to be or do. 

So probiotic sellers make wild claims, label their products inaccurately, and don’t always ensure that the product actually works at all. 

A 2011 overview of veterinary probiotics found that of 25 products tested, only two of them had accurate labels that both identified the organisms and actually contained what the label described. A full thirty-two percent of products misspelled at least one of the names of the organisms they purportedly contained. 

With under 30% of products meeting their viability promises and most of the products not even containing what they said they’d contain, a grand total of 8%—two of the twenty-five products—“had both an acceptable label and viable bacterial growth that met or exceeded label claims.”

The best probiotics for cats are alive—viability is critical.

How do you know if probiotics are alive or not?

One option is popularly called the milk test. You sprinkle some of the supplement into a bowl of milk, let it sit out for a day, and then come back to check for signs of fermentation. If the milk turned into yogurt, the probiotics are good. If it’s still thin and milky, ding-dong the probiotics are dead. Except it doesn’t work that way.

The milk test is a decent at-home way to test the viability of certain probiotic strains, like lactobacillus strains used in yogurt, it’s not effective for every type of probiotic and sometimes it gives a false positive or a false negative. Some non-probiotic additives can produce this reaction and others don’t ferment milk. 

In reality, it’s almost impossible to verify that the probiotics are viable at home. Viability guarantees and company reputation will have to do.

Does refrigeration increase viability?

Some probiotic labels recommend that you refrigerate the product to keep it fresh. Others don’t. Commonly, those probiotics which require refrigeration are considered superior products, but that’s not necessarily true.

Some probiotics simply don’t need refrigeration at all. Those stored in blister packs, for example, stay viable for a long time without refrigeration. Just like you wouldn’t refrigerate a Mountain House® dinner before it was rehydrated, there’s no need to refrigerate a freeze-dried probiotic product. Some spore-forming bacteria and yeasts also don’t need refrigeration. 

So yes, many probiotics do last longer when refrigerated and it doesn’t seem that refrigeration will hurt, but “refrigerate for best results” isn’t always a marker of superior quality. That said, sometimes it is. Unless your probiotic is one of the types outlined above, refrigeration is definitely a good idea. Better companies detail the best freshness protocol for the strains used in their product.

What is the best probiotic for cats? Here are our top 6 recommendations.

Nom Nom Probiotic for Cats

Few probiotics for cats are formulated according to any stringent NomNomNow Probiotics for Catsstandards or come with any quality assurance. This probiotic supplement appears to be one of the more trustworthy, coming from a company that’s active in microbiome research. It’s formulated with a veterinary nutrition and microbiology team and manufactured in an FDA-registered facility under GMP guidelines.

Each serving provides 20 billion CFUs with four different strains represented among them. These strains are Enterococcus faecium, Lactobacillus acidophilus, Bifidobacterium longum, and Lactobacillus plantarum. 

The probiotic bacteria are complemented by Fructooligosaccharide as a prebiotic.


  • Contains probiotic strains with known benefits for cats
  • Backed by expert formulation and research


  • Not a very well-known product—lacks a significant body of customer reviews to learn from
  • One of the most expensive probiotics for cats

Purina Pro Plan Fortiflora Probiotic for Cats Purina FortiFlora Probiotics for Cats

Perhaps the most well-known cat probiotic on the market, Purina Fortiflora comes veterinarian-recommended and cat-approved. It has only one strain—Enterococcus faecium—and only 500 million live microorganisms, but by using a well-researched probiotic and encapsulating it to ensure viability, Purina has made this a reliable, consistent product that tends to work. 

It can be a good option for cats with diarrhea, but its biggest strength is as a palatant. Fortiflora contains animal digest, which gives it all the irresistibility of crushed Temptations.  

Fortiflora is an extremely popular product both as a food topper and probiotic, with thousands of customers saying it helped their cats.


  • Extremely palatable —can help cats who have lost their appetite or to attract cats to eat new foods
  • Uses a well-researched probiotic with known benefits for cats
  • Comes from a reputable company
  • Gets excellent reviews


  • Quite expensive

Hyperbiotics PRO-Pets Hyperbiotics Pro Pets Probiotic for Cats

This probiotic supplement is encapsulated in small pearls for maximum viability and survival. The pearl has a beef flavor that cats seem to like and its small size makes it particularly easy to dose and serve. 

Each pearl provides 3 billion CFUs and includes six species of bacteria. Those bacteria include Bifidobacterium lactis, Enterococcus faecium, Lactobacillus acidophilus, Lactobacillus plantarum, Bifidobacterium longum, and Lactobacillus reuteri.

Compared to other probiotic supplements for cats, this one seems to be a bit cheaper than the rest. It doesn’t make any dramatic claims and has a good rating on FakeSpot, so it seems that the overwhelmingly positive customer sentiment is legitimate.


  • Gets positive customer reviews
  • High survivability and viability
  • Easy to dose and administer
  • High CFU count and varied bacteria


  • Some cats don’t like the pearl-style capsules

Jarrow Formulas Pet Dophilus Powder Jarrow Pet Dophilus Probiotics for Cats

Jarrow is an essential brand in probiotic supplements for both humans and cats. The Pet Dophilus product contains 5 types of probiotic bacteria and 1 billion CFUs per ¼ teaspoon serving. 

Jarrow uses substrains of well-known, well-researched probiotic bacteria. The substrains contained in Pet Dophilus are L. casei KE-0, E. faecium PF710, P. acidilactici PF7103, L. acidophilus La-14, B. animalis subsp lactis B1-04.

These probiotics are synergized with inulin and metabolin. Inulin is a prebiotic fiber that helps to support the growth of beneficial bacteria. Metabolin is a supernatant powder, which helps to increase the efficacy of the probiotic bacteria. Pet Dophilus is a popular product that gets positive customer reviews. 


  • Powder is easy to stir into your cat’s food
  • A trusted product that receives positive customer reviews
  • Contains several well-researched strains of bacteria
  • One of the most affordable pet probiotics on the market


  • Some cats don’t like the way the powder tastes

NOW Acidophilus Two Billion Acidophilus Probiotics for Cats

Probiotic supplements for humans are often more reliable and more standardized than those sold for pets. This supplement contains L. acidophilus, which has demonstrated an effect on the population of beneficial bacteria in the gut and can improve the way that cells in the body handle waste products. 

It is a good option for cats who have undergone antibiotic therapy and is among the probiotic bacterial strains that could have benefits for cats with allergies. 


  • A well-known, safe product
  • Contains a bacterial strain with demonstrated benefits for cats
  • Affordable
  • Potent and appears to have high viability


  • Doesn’t have a cat-friendly taste

NOW Saccharomyces Boulardii S. Boulardii Probiotics for Cats

This non-colonizing yeast is one of the safest and most effective probiotic products you can give your cat. It is particularly appropriate for cats with acute or chronic diarrhea. 

The product is well-respected with great customer reviews. It isn’t marketed for cats, but that is a good thing! Products for people tend to be more reliable, undergo more stringent testing, and are more standardized. This product, for example, adheres to the standards set by the FDA, Natural Products Association, and Good Manufacturing Practices.

Each capsule contains 5 billion CFUs. 


  • A well-known, well-researched probiotic
  • Receives positive customer reviews


  • Doesn’t have a cat-friendly flavor

Probiotics alone aren’t enough. 

Remember that a healthy gut results from a healthy lifestyle. This means eating the right food, having the right hygiene, exercising, and even reducing stress.


We know that, for humans, a varied diet with plenty of fresh fruits and vegetables promotes a healthy gut flora. But cats are very different from us and a diet rich in fruits, nuts, and vegetables is simply not the right choice for them.

We do know that cats who consume a carbohydrate-laden diet tend to have a gut microbiome full of sugar-loving bugs. This could lead to inflammation and possible health problems. Though we’re still not sure exactly how these microorganisms affect health, we know that cats who eat a high-protein diet are more likely to have certain gut bacteria.


In addition to the food your cat eats normally, you may want to supplement his diet with prebiotics. 

While probiotics add to the population of beneficial gut bacteria, prebiotics help your cat’s gut bacteria flourish. Gut bacteria consume prebiotic fiber and then release short-chain fatty acids in a process called fermentation. 

All prebiotic matter is fiber, but not all fiber is prebiotic. Sources of prebiotic fiber include chicory root, dandelion greens, Jerusalem artichoke, barley, and apple skin.

Prebiotics don’t choose which organisms get the honor of eating them. If your cat tends to be a bit yeasty, prebiotic supplementation pours oil onto that fire. If your cat has any other type of bacterial imbalance, prebiotic supplementation might feed the bad bacteria and tip the scales further in a very bad direction.

Dental Hygiene

What? Dental hygiene? What does brushing your cat’s teeth have to do with the health of his gut flora? Considering that the entire body, from teeth to toes, represents a microbial ecosystem, maintaining a healthy bacterial population in one place could help good bacteria to thrive everywhere else. 

At advanced stages of periodontal disease, bacteria from your cat’s mouth seeps through his gums and into his bloodstream, beginning its slow, toxic swim through the body.

Outdoor Adventures (yes, really!)

Playing outdoors exposes your cat to a variety of bacteria and other microbes that he wouldn’t encounter inside. Outdoor activity is also a great way to get some exercise and mental stimulation, both of which may have a positive effect on the microbiome. 

Closing Thoughts

Probiotics are among the most promising supplements you can give your cat. Because they interact with the microbiome, we know that they have the potential to positively influence everything from mood to diarrhea to cravings and constipation. But with the world of pet probiotics plagued with shysters, charlatans, and unfounded claims, it can be difficult to find trustworthy products. As we learn more about the feline microbiome and how probiotics can help, this industry should become more consistent and the products even more beneficial. For now, we can get great benefits out of human and feline probiotic supplements with high CFU counts, well-researched strains, and an honest reputation for excellence. These trusted products can help cats with diarrhea, constipation, irritable bowel disease, and perhaps allergies.

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