When the Vet Said There Were No Good Options
Marcus Webb had tried everything. His nine-year-old Akita mix, Bruno, had developed a hair-trigger reactivity in the years after turning seven — lunging at strangers on leashes, snapping at the vet's technicians, becoming difficult to manage in the Austin, Texas apartment complex where they lived. The behaviorist recommended prescription medication. The trainer recommended a different method. Marcus, who worked as a high school science teacher, wanted something less invasive before committing to pharmaceuticals. He started Bruno on a daily CBD oil in the spring of 2023. By the following winter, he noticed something he couldn't entirely explain: Bruno was still reactive, but the intensity of the reactions had softened. He mentioned it to a friend who kept dogs.
"I thought I was imagining it," he said. "But it kept being true."
He wasn't imagining it.
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The Largest Study of Its Kind
In November 2025, researchers from Arizona State University, the University of Tennessee, and the Dog Aging Project Consortium published findings that gave Marcus's observation a data backbone. Scientists analyzed data entered about 47,355 dogs between 2019 and 2023, in which owners reported how often they gave their dogs CBD or hemp supplements. They found that after prolonged use, dogs receiving supplements were reported to have below-average aggression levels compared with dogs with no CBD use. The study was published in Frontiers in Veterinary Science.
The analysis found that 7.3% of U.S. pet owners had given their dogs CBD or hemp supplements, with 2,759 dogs — about 5.8% of CBD users — receiving a daily dose.
The profile of the typical CBD dog was telling. Dogs receiving CBD were on average three years older than non-CBD dogs. The highest CBD usage was among dogs with dementia (18.2%), osteoarthritis (12.5%), and cancer (10%). These were not healthy young dogs whose owners were experimenting recreationally. They were aging, ailing animals whose owners were searching for something that worked.
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The Unexpected Finding
The aggression result surprised the researchers themselves. Senior project author Dr. Maxwell Leung at the Cannabis Analytics, Safety and Health Initiative at Arizona State University said:
"Behaviorally, dogs given CBD products for multiple years are initially more aggressive compared to dogs not receiving those products, but their aggression becomes less intense over time."
That last phrase is important. The dogs who ended up on CBD were, at the start, more aggressive than average. Owners had turned to the supplement precisely because they had a behavior problem. Yet the data showed that over the course of months and years of consistent use, those same dogs' aggression scores declined — moving closer to, and eventually below, the levels seen in dogs who had never received CBD at all.
Co-author Dr. Julia Albright at the University of Tennessee offered a possible explanation:
"Most canine aggression is related to underlying stress or anxiety — a fight-or-flight response that kicks in. It is unclear why only aggression but not other types of anxious or agitated behaviors seemed to be improved with CBD treatment."
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What the Study Doesn't Prove
This is important: the study is observational, not a clinical trial. It doesn't establish that CBD caused the reduction in aggression — only that a strong association exists across a very large sample over multiple years. Dr. Joseph Wakshlag, a professor at Cornell University College of Veterinary Medicine, said the results should be taken with a grain of salt. Other factors — concurrent training, veterinary treatment, the natural mellowing that can come with age — could also explain part of the trend.
For other behaviors, including agitation and general anxiety, no similar effect was observed. CBD, the data suggest, is not a broad behavioral solution. It may be specific to aggression — and even then, the mechanism isn't fully understood.
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What It Means for Dog Owners
What the study does offer is something genuinely rare in the pet supplement space: a large-scale, multi-year signal from real dogs living in real homes. Most supplement research involves small groups in controlled conditions. This one tracked nearly fifty thousand animals across four years of daily life.
For owners of older, reactive dogs — the Marcus Webbs of the country, managing a difficult senior animal and wondering whether they're doing the right thing — that signal matters. It doesn't replace veterinary guidance. It doesn't make CBD a cure. But it suggests that for some dogs, the patience required to stick with a daily supplement long enough to see results may be worth it.
Bruno is eleven now. He still doesn't love strangers. But he sits at the end of the leash rather than pulling toward them.
