What is the best probiotic for a cat with diarrhea?
Cats have better probiotic evidence than dogs: a 217-cat placebo trial of SF68, two antibiotic trials, an open-label Proviable-DC study, and a S. boulardii result. What each showed.
Quick answer
FortiFlora Feline has the strongest cat evidence of any product in this catalog. In a double-blinded placebo crossover of 217 shelter cats, 7.4% of cats on Enterococcus faecium SF68 had diarrhea lasting two days or more against 20.7% on placebo, and two trials in cats on amoxicillin-clavulanate found lower diarrhea scores and a normalized dysbiosis index. Proviable-DC improved fecal scores in 53 cats with chronic diarrhea, but without a placebo group. For a cat that is vomiting as well, off water, or passing blood, it is a vet visit first.
How the evidence ranks
| Product or strain | Trial | What it showed |
|---|---|---|
| FortiFlora Feline (SF68) | Double-blinded placebo crossover, 217 shelter cats, 4 + 4 weeks | Diarrhea of 2+ days in 7.4% vs 20.7% (P=.0297) |
| FortiFlora Feline (SF68) | Controlled, 27 cats on amoxicillin-clavulanate, 14 days | Diarrhea scores days 1–11 lower (P=0.0058); fecal score above 5 in 69% vs 86% |
| FortiFlora Feline (SF68) | Randomized placebo-controlled, 27 cats, same antibiotic | Dysbiosis index normalized by day 14 (P=0.0322) |
| Proviable-DC | Open-label, 53 cats with chronic diarrhea, 21 days | Fecal score 6.0 to 4.4 (P<0.001); 72% of owners saw improvement; no placebo |
| Proviable-DC | Randomized placebo crossover, 16 healthy cats on clindamycin, 3 weeks | All finished the antibiotic course on the synbiotic vs half on placebo (P=0.04) |
| S. boulardii DSM 34246 | 14 healthy cats, 35 days | Fecal score 3.5 vs 4.3 (P=0.0006); dry matter 46% vs 33% |
| Feline-origin E. hirae 1002-2 | 130 fostered shelter kittens | 3.4 times less likely to develop diarrhea (P=0.022); no commercial product |
SF68: the one with a placebo-controlled result in cats
The shelter trial is the reference point. 217 cats and 182 dogs were given E. faecium SF68 or placebo for four weeks, washed out for a week, then crossed over for four more. Among the cats, 7.4% on the probiotic had diarrhea lasting two days or more against 20.7% on placebo (P=.0297); the dogs showed no detectable difference (Bybee et al., 2011). Two later trials put the same product against an antibiotic: in 27 cats given amoxicillin-clavulanate for a week, 14 days of FortiFlora lowered the total diarrhea score over days 1 to 11 (P=0.0058), with 69% of probiotic cats and 86% of placebo cats reaching a fecal score above 5 (Torres-Henderson et al., 2017), and a 2026 randomized placebo-controlled trial of the same design found the dysbiosis index back to normal by day 14 on SF68 but not on placebo (Slaughter et al., 2026).
Proviable-DC: improvement, but no placebo group in the diarrhea study
53 cats with chronic diarrhea took one Proviable-DC capsule a day for 21 days in an open-label study: the mean fecal score fell from 6.0 to 4.4 (P<0.001) and 72% of owners reported improvement, with no placebo group to separate the product from time and attention (Hart et al., 2012). Its placebo-controlled evidence is in healthy cats on antibiotics: all 16 cats given clindamycin finished the three-week course on the synbiotic against half on placebo, with food intake better preserved (Stokes et al., 2017); vomiting was numerically but not significantly less (Whittemore et al., 2018).
Other findings worth knowing
Saccharomyces boulardii firmed stools in 14 healthy cats over 35 days, with a fecal score of 3.5 against 4.3 on control (P=0.0006) and fecal dry matter of 46% against 33% (Lonigro et al., 2025); the US cat products carry a different S. boulardii strain, so this is ingredient-level evidence. A feline-origin Enterococcus hirae strain made 130 fostered shelter kittens 3.4 times less likely to develop diarrhea (P=0.022), but no commercial product carries it (Gookin et al., 2022). Chews built on Bacillus coagulans have no trial in cats.
Signs to stop comparing products and call the vet
Vomiting or diarrhea more than twice in 24 hours or with obvious illness, blood in the stool or vomit, black tarry stool, straining without passing stool, refusing water for a day, or a cat that is weak or hiding and off food: the veterinary sources treat these as emergencies or reasons for an examination, and the quiz stops on them. Kittens under six months with diarrhea go to the vet before any product.
Products in this catalog with the trials above
- Purina Pro Plan Veterinary Supplements FortiFlora Feline — cats, $1.03 a day
- Nutramax Proviable-DC capsules — dogs and cats, $0.56 a day
- AnimalBiome S. boulardii + FOS Powder for Cats and Dogs — dogs and cats, $0.89 to $4.45 a day by weight
- VetriScience Probiotic Everyday (Gut Health) for Cats — cats, $0.17 a day
- Fera Pets USDA Organic Probiotics with Prebiotics — dogs and cats, $0.25 to $1.00 a day by weight
Common questions
What is the best probiotic for cat diarrhea?
FortiFlora Feline (Enterococcus faecium SF68) has the strongest evidence: 7.4% of cats on it had diarrhea of two days or more against 20.7% on placebo in a 217-cat shelter trial, and two trials in cats on antibiotics found lower diarrhea scores and a normalized dysbiosis index. Proviable-DC improved fecal scores in 53 cats with chronic diarrhea but had no placebo group.
Does FortiFlora work for cats?
In the trials, yes: fewer cats with diarrhea against placebo in a shelter, lower diarrhea scores and a normalized microbiome in cats on amoxicillin-clavulanate. Its evidence in cats is stronger than in dogs.
How long does it take for a probiotic to help a cat’s diarrhea?
The shelter trial measured over four weeks; the antibiotic trials saw lower diarrhea scores across the first 11 days and a normalized dysbiosis index by day 14; the Proviable-DC study ran 21 days. Diarrhea that is worsening, bloody or paired with vomiting is a vet visit rather than a wait.
Is Proviable-DC good for cats?
It improved fecal scores from 6.0 to 4.4 in 53 cats with chronic diarrhea over 21 days, without a placebo group, and in a placebo-controlled crossover it helped healthy cats tolerate a course of clindamycin. That is real but weaker than the SF68 evidence.
Can cats have Saccharomyces boulardii?
It was given to 14 healthy cats for 35 days and firmed their stools against control (fecal score 3.5 vs 4.3). The strain tested is not the one in the US pet products, so treat it as ingredient-level evidence.
Sources
- Bybee SN, et al. Effect of the probiotic Enterococcus faecium SF68 on presence of diarrhea in cats and dogs housed in an animal shelter. J Vet Intern Med. 2011. pubmed.ncbi.nlm.nih.gov/21689152
- Torres-Henderson C, et al. Effect of Enterococcus faecium strain SF68 on gastrointestinal signs and fecal microbiome in cats administered amoxicillin-clavulanate. Top Companion Anim Med. 2017. pubmed.ncbi.nlm.nih.gov/29291771
- Slaughter A, et al. Enterococcus faecium SF68 and the fecal microbiome of cats given amoxicillin-clavulanate. J Feline Med Surg. 2026. pubmed.ncbi.nlm.nih.gov/41923274
- Hart ML, et al. Open-label trial of a multi-strain synbiotic in cats with chronic diarrhea. J Feline Med Surg. 2012. pubmed.ncbi.nlm.nih.gov/22412160
- Stokes JE, et al. Randomized, controlled, crossover trial of prevention of clindamycin-induced gastrointestinal signs using a synbiotic in healthy research cats. J Vet Intern Med. 2017. pubmed.ncbi.nlm.nih.gov/28755457
- Whittemore JC, et al. Effects of a synbiotic on the fecal microbiome and metabolomic profiles of healthy research cats administered clindamycin. PeerJ. 2018. pubmed.ncbi.nlm.nih.gov/30038854
- Lonigro N, et al. Saccharomyces boulardii DSM 34246 in healthy cats. 2025. pubmed.ncbi.nlm.nih.gov/39852919
- Gookin JL, et al. Randomized placebo-controlled trial of feline-origin Enterococcus hirae probiotic in shelter kittens. 2022. pubmed.ncbi.nlm.nih.gov/36467638
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