The canine gut–brain axis is biologically plausible and increasingly studied, but clinical evidence that probiotics reduce anxiety in dogs is still early. A 2025 randomized placebo-controlled trial reported improvements in anxiety-related measures with one specific Lactiplantibacillus plantarum strain, while earlier canine work often involved multi-ingredient formulas rather than a probiotic alone.
The correct interpretation is therefore promising but strain-specific, not “probiotics calm dogs.”
Key takeaways
- Canine behavior and gut microbiome research is expanding.
- One 2025 randomized placebo-controlled trial found anxiety-related improvement with L. plantarum LP815™.
- The trial was small and exploratory, with 40 dogs and unequal group sizes.
- Earlier positive studies often tested multi-ingredient nutraceuticals, so they cannot isolate a probiotic effect.
- GABA production, vagal signaling or microbiome changes are mechanisms, not clinical outcomes.
What the 2025 LP815 trial found
Forty home-based dogs were enrolled in a randomized placebo-controlled study. Twenty-eight received Lactiplantibacillus plantarum LP815™ and 12 received maltodextrin placebo for four weeks.
Behavior was assessed with C-BARQ and activity monitoring. Between-group differences favored LP815 on several anxiety/aggression measures, and exploratory general-anxiety analyses also favored treatment.
This is the clearest direct dog-specific probiotic signal currently available for this question.
Why one positive strain does not prove the category
Probiotic effects are often strain-specific.
Evidence for:
Lactiplantibacillus plantarum LP815™
does not automatically support:
- another L. plantarum strain;
- a different bacterial species;
- a multi-strain probiotic;
- a synbiotic containing unrelated organisms.
The study was also modest in size and not publicly preregistered, and some analyses were exploratory. Those limitations should remain visible.
What about earlier gut–brain studies?
Some canine studies have reported behavioral improvement alongside microbiome changes after multi-ingredient nutraceutical formulas containing probiotics, prebiotics, postbiotics, amino-acid precursors and other ingredients.
Those studies are useful formula-level evidence, but they cannot establish that the probiotic component caused the behavioral change.
Mechanism is not outcome
Potential pathways include:
- microbial metabolite production;
- vagal signaling;
- immune modulation;
- GABA-related pathways.
These mechanisms can explain why research is being done. They do not prove a dog becomes less anxious.
Dog Supplement Facts evidence status
INSUFFICIENT — EARLY SUPPORTIVE, STRAIN-SPECIFIC EVIDENCE
One small RCT is not enough to support a broad category claim.
What the evidence does not prove
- probiotics generally treat canine anxiety;
- LP815 evidence applies to other strains;
- microbiome changes equal behavioral improvement;
- a probiotic should replace behavioral therapy or prescribed medication;
- a multi-ingredient calming formula proves probiotic efficacy.
Related Dog Supplement Facts content
- Dog Calming & Stress Guide
- Alpha-Casozepine for Dogs
- Tryptophan for Dogs
- How to Check a Dog Calming Supplement Label
References
- Efficacy of a novel Lactiplantibacillus plantarum strain (LP815™) in reducing canine aggression and anxiety: a randomized placebo-controlled trial. Animals. 2025. PMID 40805070.
- Gut-brain axis impact on canine anxiety disorders: new challenges for behavioral veterinary medicine. Review, 2024.
- Relevant multi-ingredient canine nutraceutical studies should be treated as formula evidence only.