Several times in the past, I have written about he potential usefulness of cranberry extract in various forms for treating or preventing urinary tract infections (UTI) in dogs and cats. The last time I covered the subject was way back in 2017, and the evidence was still not conclusive, in veterinary patients or humans:
There is weak theoretical justification for using cranberry products for UTIs, though none of the supporting preclinical evidence involves dogs or cats. There is conflicting clinical trial evidence in humans, and no clinical studies in dogs and cats.
This [Cochrane] review indicates pretty clearly that overall, cranberry juice is not effective in preventing UTIs despite theoretical reasons why it might be. This illustrates, yet again, why we cannot rely on extrapolation from pre-clinical or in vitro studies to tell us what will work in actual patients.
The in vitro portion of this study is consistent with existing research that suggests cranberry extracts may reduce the ability of some bacteria to stick to the lining of the urinary tract. This could theoretically help prevent some urinary tract infections, though clinical research in human patients suggests this doesn’t really work to a significant extent in living people.
The portion of the study looking at prevention of UTIs in actual dogs, unfortunately, doesn’t help establish what benefit, if any, this product might have.
Despite some promising laboratory studies suggesting cranberry supplements might help prevent or treat urinary tract infections, the evidence of studies in clinical patients has been disappointing. Conflicting studies in humans suggest, on balance, that there is probably no significant benefit. And now a high-quality clinical trial in dogs has failed to find any effect, even in the the of infections the pre-clinical research most strongly suggested there should be one.
While the risks of cranberry supplements are probably negligible, pet owners should understand, and veterinarians should make in clear to their clients, that there is no good reason to believe they have any real value in preventing or treating urinary tract infections.
Here we are nine years later. Surely, the question must have been answered definitively by now? Yeah, about that…
A recent systematic review evaluated the research evidence to date on the topic.
Weese JS, Weese HE. Effectiveness of Cranberry Supplementation for Prevention and Treatment of Infectious Urinary Tract Disease in Dogs and Cats: A Systematic Review. J Vet Pharmacol Ther. 2026 Feb 12.
The conclusion is quite familiar:
Limited data are available regarding the use of cranberry or cranberry extracts for the prevention or treatment of infectious urinary tract disease in dogs and cats…While indirect evidence from humans and in vitro data from dogs and cats suggests the potential for efficacy, the small number of studies, small sample sizes within those studies, and low certainty of evidence preclude confident assessment of the role of cranberry for the prevention or treatment of infectious urinary tract disease in dogs and cats.
Despite decades of claims, research, and clinical use in patients, we still can’t say with any confidence whether or not cranberry, in whatever dose and form, is at all useful.
This is a common situation in veterinary medicine, where resource limitations and cultural factors rarely allow for large-scale, robust scientific evidence to answer such questions with confidence. However, in this case, the greater resources and efforts made in humans haven’t proven a whole lot better.
A recent systematic review evaluated studies in thousands of humans and found some evidence of benefits, with lots of caveats.
- Cranberry juice reduced the rate of UTIs about 27% compared with a placebo liquid and appeared to improve symptoms somewhat.
- Cranberry juice also appeared to reduce the use of antibiotics by about half compared with a placebo liquid.
- Other forms of cranberry supplement didn’t seem to be helpful.
- The evidence for benefit was only moderately certain.
- Another recent review found similar benefits, but not for certain groups, including elderly people in institutions and people with neurological conditions impairing their urination.
Bottom Line
The inconclusive nature of the veterinary research, and the caveats and nuances of the human literature, make it effectively impossible to say whether any form of cranberry supplement will benefit individual dogs or cats at risk for UTI. There is no evidence for significant safety concerns, and if using these products reduces excessive or inappropriate antibiotic use in patients with urinary tract disease, that might be an indirect benefit. Still, it is frustrating that we still cannot have confidence in the effects of these products, and should remain skeptical of the claims made for them by manufacturers and others with opinions based on anecdotal evidence.
