Sugarless Candies Can be Toxic to Pets
Candies containing xylitol have been recognized by the National Animal Poison Control Center to be a risk to pets. This compound can cause liver damage and death in dogs susceptible to being poisoned with xylitol. If your dog ingests sugarless candy it would be best to contact the NAPCC (1-888-426-4435).
It is possible your vet will not be familiar with this source of poisoning as this information is fairly new and candies have not usually been associated with poisonings in dogs if they did not contain chocolate as the major ingredient.