A service animal is an animal that is trained to perform one or more assistive tasks, to assist someone with a health defect, disease or disability. Service animals are protected by the ADA and their cost, training and upkeep are deductible medical expenses.
A "therapy" animal is one that provides comfort through its natural behaviors, and is not trained to perform tasks. There is no recognized definition of a therapy animal, and therapy animals are not covered by the ADA. I don't know of any specific tax court cases, but I believe that since therapy animals are not covered under the ADA and are not trained to assist people with disabilities, they are not deductible medical expenses. But that's my opinion, as I said, I don't think there is a tax court case on this yet.
