Rachel Martinez started giving her twelve-year-old Labrador, Bailey, CBD oil in March 2024. Bailey had arthritis in both hips, and pain medication wasn't working well. Within three days, Bailey snapped at Rachel's husband when he reached for her food bowl. Bailey had never done that before. A week later, Bailey growled at another dog at the park. Rachel stopped the CBD immediately, convinced it was making Bailey aggressive.

She didn't know she'd quit right before the behavior would have improved.

A study published in November 2025 in Frontiers in Veterinary Science analyzed data from 47,355 dogs enrolled in the Dog Aging Project. The findings revealed something unexpected: dogs given CBD products initially showed increased aggression compared to dogs not receiving CBD. But over time, that pattern reversed. Dogs on long-term CBD showed reduced aggression.

"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," said Dr. Maxwell Leung, director of the Cannabis Analytics, Safety and Health Initiative at Arizona State University, who led the study.

"This long-term behavioral change highlights the potential of CBD as a therapy for canine behavioral issues."

The study represents the most extensive effort to investigate CBD use among pet dogs in the United States. Researchers analyzed survey data collected between 2019 and 2023. Of nearly 50,000 dogs tracked, 7.3 percent had been given CBD or hemp products. Of those, 2,759 dogs were frequent users, receiving CBD daily.

The demographics revealed clear patterns. Dogs receiving CBD were, on average, three years older than dogs that didn't receive it. The strongest association appeared in dogs with dementia, where 18.2 percent were receiving CBD. Dogs with osteoarthritis followed at 12.5 percent, and dogs with cancer at 10 percent.

Marcus Chen from Seattle started giving his fourteen-year-old German Shepherd, Ranger, CBD in early 2023 after a cancer diagnosis. Ranger had become more irritable as his health declined. The CBD seemed to make it worse at first. Ranger's irritability spiked during the first month. But Marcus had read about the adjustment period and decided to stick with it. By month three, Ranger's aggression had noticeably decreased. By month six, he was calmer than he'd been in over a year.

"I almost stopped during that first month. But my vet told me to give it time. I'm glad I did."

The study also uncovered geographic and gender patterns. Dogs living in states where medical cannabis is legal for humans were more likely to receive CBD, suggesting owners' attitudes toward cannabis influence their pet decisions. Male dogs were 9 percent more likely to receive CBD than female dogs.

Dr. Julia Albright, an associate professor at the College of Veterinary Medicine at the University of Tennessee and co-author, emphasized the significance of the long-term behavioral shift. "This research shows that CBD may offer therapeutic benefits for dogs with behavioral issues, but it's not a quick fix. Owners need to understand there may be an adjustment period before they see positive results."

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The initial increase in aggression remains puzzling. One hypothesis is that CBD affects dogs' sensory processing or pain perception in ways that temporarily heighten reactivity. As dogs adjust over weeks or months, the underlying mechanisms that reduce aggression—potentially related to anxiety reduction or pain relief—begin to dominate.

Lisa Rodriguez from Austin gave her ten-year-old Beagle, Scout, CBD for separation anxiety in mid-2024. Scout became more reactive to noises during the first few weeks. But Lisa persisted, and by two months, Scout's anxiety had noticeably decreased. By four months, Scout was calmer than she'd been in years.

"I think a lot of people give up too early. If I'd stopped after the first month, I would've thought it didn't work. But it did. It just took time."

The study's findings don't provide definitive answers about CBD's mechanisms or effectiveness for every dog. The research was observational, tracking what owners were already doing rather than administering controlled doses. But the scale—nearly 50,000 dogs over multiple years—offers valuable insights into real-world CBD use patterns.

For Rachel in Phoenix, the findings came too late. She'd already decided CBD wasn't right for Bailey after the initial aggression spike. Bailey's arthritis worsened over the following year. When Rachel learned about the study's findings in late 2025, she wondered if Bailey's aggression would have improved if she'd waited a few more weeks.

"I wish I'd known. I might have made a different choice."

The study highlights a challenge in pet health: the gap between emerging research and owner decision-making. CBD products are widely available and increasingly popular. But scientific understanding is still catching up. The long-term reduction in aggression suggests CBD may offer real therapeutic potential. But the initial increase means owners need to be prepared for a rocky start—and willing to wait through it.