Many people use peanut butter as a treat, to stuff a Kong or to disguise medicines for their dogs. In a bid to reduce sugars in many 'human' foods sweeteners are being added. Most sweeteners will have an adverse effect to dogs health, but Xylitol is toxic to dogs and consumption can be fatal. Please ensure that you check the ingredients of any foods. Some peanut butters are now being made with these harmful [to dogs] additives. If you think your dog has consumed Xylitol please contact your vets immediately.