allergys?

Question
I have a 1year old cat that started scratching constantly after he was about 6 months old.  My vet said it was a food allergy and put him on Prescription Diet.[Hills] ZD and gives him a shot of depo-medrol every 5 or 6 weeks.  Some times it doesn't even last that long.  First are there any long term affects of this drug, and is there any other food that might help. If it isn't a food allergy how do I find out what is is?  Do you have any ideas?  Thank you.

Answer
There are many foods that treat food allergies in cats, but z/d is really the best.....as long as that is the ONLY food the cat gets.  Any treats will negate the effects of z/d.  Most cats with food allergies scratch at their ears or face.

Depo medrol is fairly safe in the cat.  If it is not long lasting, it may not be an allergy at all, but a parasite like scabies or otodectes (ear mites on the skin).  Ask your vet to treat for these parasites and see if it makes a difference.