I first wrote about the subject of probiotics in 2009, and I have added quite a few articles on the subject since (1, 2, 3, 4, 5,6, 7, 8, 9, 10, 11). Overall, the evidence has been mixed but pretty poor for most conditions. The best evidence suggests some possible benefit for acute gastrointestinal problems such as diarrhea, but the veterinary probiotic literature is sparse and poor quality, with significant risk of bias, particularly given that almost all studies are funded by companies selling probiotic products. There is also evidence that the quality of probiotic products available for dogs and cats is poor.
The most recent product to enter this area is a bit different from others in that it is explicitly intended to treat behavioral problems, rather than the more typical gastrointestinal disease. Purina Calming Care is promoted “to help dogs maintain calm behavior. It supports dogs with anxious behaviors and helps them cope with external stressors like separation, unfamiliar visitors, novel sounds or changes in routine and location. It also helps dogs maintain positive cardiac activity during stressful events, promoting a positive emotional state.”
The idea that a probiotic might help with diarrhea of chronic GI disease is fairly intuitive, but the claim that feeding specific microorganisms can influence behavior seems a bit more farfetched. However, there turns out to be quite a bit of evidence in lab animals and humans that the ecology of the GI tract does have significant effects on the chemistry of the central nervous system, and the mood and behavior that results.1,2 There are also a number of reviews of experimental studies in humans specifically evaluating probiotics as treatments for anxiety and depression, and while there are plenty of limitations and lots of inconsistency, the evidence is actually fairly encouraging.2–7
Of course, the devil is in the details, and even in humans it is difficult to say with confidence that any given probiotic will help any specific patient. Though there is some positive clinical research, the studies use different probiotics in different forms for different populations with different problems, and this heterogeneity makes generalizations about the value of probiotics for mood disorders unreliable. In veterinary medicine, the situation is considerably worse since the evidence is far less robust.
There are no fully peer-reviewed studies of probiotics for behavioral problems in dogs or cats. The best we have is an abstract of a Purina study evaluating their Calming Care product in dogs. Twenty-four dogs described as “anxious” (no more formal diagnosis was given) were tested with and without the product over six-week periods. Purportedly blinded observations of behavior and measurements of objective markers such as heart rate and cortisol levels in saliva all showed changes during the period on the probiotic that would suggest a beneficial effect. However, the information about how the study was conducted is too limited to effectively appraise its quality, and of course it is an in-house study run by the company to provide marketing material for their own product, so potential bias is certainly a concern.
As I have pointed out previously, the risks of probiotics appear to be low, though some cases of direct injury and instances of transmission of genes for antibiotic resistance passed from probiotic organisms to pathogenic bacteria have been reported. In the face of encouraging but incomplete lab animal and human evidence and virtually no research in veterinary patients, it is not unreasonable to try a product like Calming Care for dogs with anxiety-related problems, but we can have little confidence in its effects.
1. McKean J, Naug H, Nikbakht E, Amiet B, Colson N. Probiotics and Subclinical Psychological Symptoms in Healthy Participants: A Systematic Review and Meta-Analysis. J Altern Complement Med. 2017;23(4):249-258. doi:10.1089/acm.2016.0023
2. Wang H, Lee I-S, Braun C, Enck P. Effect of Probiotics on Central Nervous System Functions in Animals and Humans: A Systematic Review. J Neurogastroenterol Motil. 2016;22(4):589-605. doi:10.5056/jnm16018
3. Nikolova V, Zaidi SY, Young AH, Cleare AJ, Stone JM. Gut feeling: randomized controlled trials of probiotics for the treatment of clinical depression: Systematic review and meta-analysis. Ther Adv Psychopharmacol. 2019;9:204512531985996. doi:10.1177/2045125319859963
4. Liu RT, Walsh RFL, Sheehan AE. Prebiotics and probiotics for depression and anxiety: A systematic review and meta-analysis of controlled clinical trials. Neurosci Biobehav Rev. 2019;102:13-23. doi:10.1016/j.neubiorev.2019.03.023
5. Wallace CJK, Milev R. The effects of probiotics on depressive symptoms in humans: a systematic review. Ann Gen Psychiatry. 2017;16(1):14. doi:10.1186/s12991-017-0138-2
6. Pirbaglou M, Katz J, de Souza RJ, Stearns JC, Motamed M, Ritvo P. Probiotic supplementation can positively affect anxiety and depressive symptoms: a systematic review of randomized controlled trials. Nutr Res. 2016;36(9):889-898. doi:10.1016/j.nutres.2016.06.009
7. Huang R, Wang K, Hu J. Effect of Probiotics on Depression: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients. 2016;8(8):483. doi:10.3390/nu8080483