This is one that many people may not know about. Last week a client called because her dog (about 16 pounds) got into her purse and ate an entire pack of chewing gum. She thought she had remembered something about it being poisonous, so she called my office. We had her check the package, and indeed it did carry the toxic ingredient. Thankfully, we were able to help her induce vomiting right away, managed to get the gum out of the stomach, and after some observation the dog was fine.
Xylitol is an artificial sweetener found in many products, but most commonly sugar-free chewing gum. In dogs it can cause a sudden drop in blood sugar, sometimes as quickly as 30 minutes, but also as long as 12 hours after ingestion. The hypoglycemia often appears as stumbling, weakness, incoordination, or other neurological signs. However, vomiting is usually the first sign of toxicity. There is also evidence that xylitol poisoning can lead to liver failure. In fact, liver disease and death are emerging as the more severe consequence. The affect on the liver can also cause severe disfunction of the blood's ability to clot properly.
Xylitol is also found as a sweetener in other products, so it's not just limited to chewing gum. The ASPCA Animal Poison Control Center has reported this poisoning after eating cookies, muffins, and cupcakes. What is interesting is that other artificial sweeteners such as saccharin, aspartame, and sucralose are generally considered safe.
This is a prime example of how animals metabolize things differently than humans. Something that is perfectly safe for people, can be potentially deadly in a pet. At first it seems like something as simple as chewing gum couldn't possibly do any harm. But this is a serious risk, and should be treated as a real danger. If you see your dog chewing gum, it could be more than just a lark. It could mean a sudden and expensive trip to the emergency room.
Here is an article on xylitol poisoning from the Animal Poison Control Center. Be warned that it's designed as continuing education for veterinarians, so a layperson may get lost in some of the language.