Obsessing isn’t just for humans. In a study out today, scientists have found evidence that dogs, too, can become addicted to certain objects—and especially, their favorite toy. The researchers observed dozens of dogs as they interacted with their most prized toys. About a third of dogs exhibited addiction-like behaviors, such as becoming especially agitated when the toy was kept from them, they found. These findings might come as no surprise to dog owners. But the researchers say their work is the first to empirically document the phenomenon. “This is the first scientific study on addictive-like behavior in dogs,” study author Stefanie Riemer, a behavioral biologist from the Messerli Research Institute for Human-Animal Interaction at the University of Veterinary Medicine Vienna, told Gizmodo. Ball junkies Riemer notes that many pet owners and trainers use a (rather on the nose, it turns out) nickname for dogs that seemingly just can’t get enough of their toys: “ball junkies.” But it’s never been clear whether this sort of behavior actually mirrors how addiction manifests in people. “After all, just being highly motivated, or highly aroused or very toy-focused does not imply an addiction,” Riemer notes. Scientists already knew that it’s possible to induce addictive-like behaviors in animals like rats, which has allowed us to better study potential treatments for substance use disorders or other addictions in humans. But it’s still an open question as to whether animals besides humans can develop addictions naturally, the authors said. To test their hypothesis, the researchers tried to apply the criteria we use to determine addiction in humans to dogs. The study involved 105 dogs, with the most common breeds being Malinois, Border Collies, and Labrador Retrievers. All of the dogs were described as toy-motivated by their owners. For the experiments, the researchers used toys the owners said their dogs would likely love the most, and also included the dog’s favorite toy at home if the owners brought it with them. Excessive and maladaptive Across all the tests, the researchers found that 33 dogs exhibited addictive-like behaviors with the toys. These behaviors included dogs staying laser focused on the toy if it was kept in the room but placed somewhere unreachable; dogs refusing to play with their owner in other ways; and even dogs turning down a free treat. “This could indicate that the high motivation for playing conflicts with other important activities—the dogs are willing to forgo other activities or rewards when they are focused on the toy, even when they cannot access it,” Riemer explained. “It shows that the toys have a high salience for these dogs and that they are craving access to these toys.” Perhaps the most illustrative example of addictive-like behavior was seen when the toys were entirely removed, she added. Some dogs were simply unable to calm down for up to 15 minutes after the toys were gone, their heart rates remaining elevated. That sort of prolonged arousal and high frustration seen in these dogs, Riemer said, suggests their motivation for toy playing could be considered “excessive and maladaptive”—an important criteria for diagnosing human addiction. The team’s findings were published Thursday in Scientific Reports. A video of one of the dogs in these tests can be seen below and on YouTube. More left to learn The researchers say their findings should be taken with some caution. It’s hard to accurately measure and classify addiction in people, let alone non-verbal animals. And there’s still much to learn about the potential nature of addiction in dogs. One important lingering question is exactly how and why these behaviors can emerge. The researchers found some evidence that the seeds for excessive toy-playing tend to show up in puppies. They’re also conducting a follow-up study examining whether certain breeds, particularly some kinds of working dogs, are more predisposed to toy addiction than others. Because this study focused on dogs already known to be toy-motivated, though, it’s not clear just how prevalent addictive-like behaviors are in dogs generally. All that said, Riemer doesn’t want owners to overly worry about their dogs if they simply love playing with their toys in healthy amounts. “Many dogs colloquially referred to as ‘ball junkies’ are just highly motivated, but they have no problems when the play is stopped,” she said. “I think toy play is a great reward for many dogs, but for the ‘extreme’ dogs, steps should be taken to reduce their fixation on toys.” Riemer is now working on a grant to explore ADHD in dogs, since it seems to have lots of parallels with addictive-like behaviors in their research. Other studies have also suggested dogs might be a good model for better understanding ADHD in people.