Both chocolate and the artificial sweetener xylitol—found in many sugar-free candies—can be toxic to dogs.
“Chocolate contains theobromine, a substance that can be poisonous to your pet. Dark, semi-sweet and Baker's chocolate can be lethal if ingested,” says Zabell.
Dogs can’t digest theobromine as efficiently as humans. Theobromine can be used medically as a diuretic, heart stimulant, blood vessel dilator, and a smooth muscle relaxant. Since dogs can’t process theobromine, excessive amounts of it can cause vomiting, diarrhea, increased thirst, panting or restlessness, excessive urination, a racing heart rate, muscle spasms and occasionally seizures, according to Shelby Neely, VMD.
“[Xylitol] can cause a life-threatening blood sugar drop or hypoglycemia in dogs. Additionally, xylitol can also cause rapid liver failure,” says Heather Loenser, DVM, and veterinary advisor, public and professional affairs, for the American Animal Hospital Association. “Dogs are most often exposed to xylitol when they accidentally eat sugar-free gum or peanut butter that contains it. I recommend that dog owners carefully read the label of all ‘sweet’ products including tooth paste, cookies and candies, and keep anything containing xylitol out of reach of a curious canine.”