Peppermint is a refreshing herb, and its oil has a host of uses, soothing an upset belly or relieving a sore muscle. When it comes to using it for your cat, there's no real consensus on its safety. The American Society for the Prevention of Cruelty to Animals advises against its use, while other animal professionals advocate peppermint oil for a variety of benefits.
Peppermint Oil and Phenols
The American Society for the Prevention of Cruelty to Animals states that cats are particularly sensitive to peppermint oil, noting the oil may cause harmful effects to the gastrointestinal system, central nervous system and liver. As well, inhaling the oil may cause aspiration pneumonia. However, the peppermint plant is not listed on the organization's toxic and nontoxic plant database as being safe -- or unsafe -- to pets. PetMD considers peppermint to be a cat-friendly plant, advocating it for home gardens.
If the contradiction leaves you confused, Dr. Jeannie Thomason of The Whole Dog helps clear up the matter by describing cats' sensitivity to essential oils. According to Dr. Thomason, cats are sensitive to essential oils that are high in phenols because they aren't able to metabolize them properly, potentially causing severe illness or death. Peppermint oil's phenols make using it a precise proposition -- a little too much can have a harmful effect on your cat -- so it should be used under veterinary direction.