Ellie Tonkin said she couldn't imagine living without her shepherd mix, Tippy, after rescuing her from an animal shelter.
"She's the greatest dog in the world," she said. "I'm just extremely attached her.
But then overnight while Tonkin slept, Tippy discovered something to eat in a purse.
"There were bits of stuff all over the room," Tonkin said. "I found some half-chewed up pieces of gum here and there."
Tippy was in trouble.
She had eaten Tonkin's Orbit gum, which lists the sugar substitute xylitol first on its list of ingredients.
"Oh yes, it can be lethal," said Dr. Virginia Sinnott, a senior staff veterinarian in the emergency department at Angell Animal Medical Center in Jamaica Plain.
She said the hospital treats about 10 cases of xylitol poisoning each month.
"This whole pack could probably make a medium-sized dog very ill," said Sinnott as she held a pack of sugar-free gum. "And a small dog, could be a lethal dose."
Brands like Mentos, Icebreakers, Pur and the new Tic Tac gum can all contain xylitol.
It's a popular ingredient in sugar-free products because some studies show that xylitol prevents cavities better than other substitutes like aspartame and Splenda.
But xylitol also can cause a medical crisis for dogs.
Their bodies still recognize xylitol as sugar, even though it's not.
"So you get this insulin spike because the body thinks it's sugar and the dog's blood sugar drops precipitously," Sinnott explained. "If the blood sugar continues to drop, the heart can stop."
When Tonkin realized what had happened, she rushed Tippy to Angell.
"When I brought her in, I was terrified," she said. "I was really shaken."
Angell monitored Tippy for two days. A week later, she was doing much better.
"There's no reason to chew gum with xylitol at this point," Tonkin said. "At least for a dog owner with a mischievous dog."
The medical director at the ASPCA Animal Poison Control Center said xylitol amounts can vary among sugar-free brands, even flavors.
The ingredient is also found in other 'human' products like certain peanut butters and toothpaste.