A recent study has found that approximately 3 percent of dogs may exhibit behavior resembling addiction to tennis balls or similar toys. These dogs become so fixated on their favored playthings that they sometimes disregard food, fatigue, pain, and their owners’ attempts to interrupt play. When separated from the toys, these animals can display signs of distress akin to withdrawal.

Conducted by researchers at the University of Bern, the study analyzed questionnaire responses from nearly 1,700 dog owners across 33 countries. The survey measured canine behaviors indicative of addiction, such as escalating tolerance—where a dog requires increasing amounts of play to feel satisfied—and signs of agitation or stress when denied access to toys. Dogs scoring 66 or higher out of 75 possible points on the questionnaire were classified as exhibiting extreme behavior, amounting to 52 animals, or roughly 3 percent of the sample.

Lead author Alja Mazzini noted that while some dogs continued to engage with toys despite exhaustion and panting, others ignored food and owner interaction even when the toy was unreachable. In one illustrative experiment, two Belgian shepherds were presented with their favorite toy locked inside a heavy container while food was freely available nearby. The dogs ignored the food and instead repeatedly bit and battered the container until it was broken open, demonstrating a relentless focus on retrieving the toy despite mounting fatigue.

Mazzini emphasized this persistent behavior could represent a welfare concern. “It was as if they were saying: ‘I don’t care. I will destroy this box and I will get the toy,’” she said. She also cautioned against removing toys altogether, highlighting that play plays a crucial role in strengthening the bond between dogs and their owners.

The study advises dog owners to watch for warning signs such as a dog’s inability to disengage from play, ongoing frustration when the toy is removed, difficulty resting, and steadily escalating arousal. Mazzini suggested that these behaviors warrant attention, saying, “If a dog consistently cannot come down after the toy is removed, remains preoccupied, becomes persistently frustrated or cannot rest, I would take that seriously.”

While the research draws parallels to human behavioral addictions like problem gambling, Mazzini noted that the precise neurological mechanisms behind these behaviors in dogs remain unclear. The findings were published in the journal Royal Society Open Science.