Some brands of peanut butter have started replacing sugar with a sugar substitute called Xylitol, which is highly toxic to dogs. However, before you start throwing throwing away the peanut butter, read the attached article. It's just a few specialty peanut butter brands. Xylitol can also be found in sugarless gum. It's always good practice to read the label before giving human foods to your pet. As always, call your vet if your pet has ingested a potentially toxic substance. Symptoms usually don't show up until hours later.