My apt. complex requires pet permission letter from a doctor or counselor for rental renewal. I've had two cats for 4 yrs. One cat is my son's, his doctor wrote him a letter, but he no longer lives here. I have very serious Diabetes, and diabetes neurapathy beyond surgery. The cats are helpful in keeping me active playing, feeding an daily brushing them. My PCP will not write a letter. She says cats are not assistive animals. I believe they are assistive in a companionship way.