Peppermint Harmful To Ferrets. Fruits have high sugar content, which means that they also contain complex carbohydrates. Unfortunately, when a dog inhales peppermint it can also cause it to have stomach upset.

The reason why peppermint oil is assumed to be a great mouse repellent is because in high concentrations peppermint can be quite potent, and mice (and rats) have a very sensitive sense of smell. Your pet may not be in danger if you use a few peppermint leaves, preferably dried mint. These are toxic whether they are applied to the skin or used in diffusers.