Many mouthwashes (and sugar free gums, candies, cough syrups and breath mints) contain a sugar substitute called xylitol. It’s completely safe for humans, but it’s extremely toxic for dogs, says Flansburg-Cruz. “Small amounts of xylitol can dangerously decrease your dog’s blood sugar levels, and cause seizures, liver failure and death,” she says. Poisoned dogs often exhibit symptoms within 30 minutes of consumption. These include vomiting, weakness, difficulty standing, depression, tremors, seizures, and coma. If your dog ingests any amount of xylitol bring her to the veterinarian immediately.