Senior Cat pulling his hair out

Question
Thanks for the info....Yes, we use Frontline on him. He's been checked for fleas and ticks.  Is the med you recommended OTC or script? Thanks!
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The text above is a follow-up to ...

-----Question-----
Hi, Karen...
I have a 15 year-old neutered male cat.  He's a recovered diabetic. He spent a week in ICU the winter of '05, was on insulin for awhile, now he's fine.  He's a very social cat and always wants to be held and never meets a stranger. He's more like a dog.

For the past 6 months or so, he's been pulling his hair out. We took him to the vet and all was well, thyroid, skin, etc.  They offered amitritpyline for anxiety but said it could cause his diabetes to flare up.

He will start grooming, then the next thing you know, he's yanking tufts of hair out.  He knows the word "NO" so when we catch him we stop it, however, we're not with him 24/7. There haven't been any changes in our household, schedule-wise, no new animals, no new furniture or carpet.

He's an indoor/outdoor cat but in winter spends about 99% of his time indoors.

Any ideas? Any feedback will be greatly appreciated.
Thanks, Carol
-----Answer-----
Hi Carol,

Have you checked him for fleas? I know this is probably one of the first things you did, but cats are real good at getting rid of fleas. And since he is an out door cat he may have picked some up that you can't see. Try using Advantage for cats and see what happens in about two weeks. If that doesn't help you can try an antihistamine for him and see if it is an allergy. Try Chlortrimeton, 4mg., 1/2 tablet 2x a day.
Write back to me and let me know how he is. Good luck.

Ciao, Karen

Answer
Hi Carol,

It's an OTC med. If you can't find it try Benadryl. But make sure you are getting just Benadryl with nothing in it. Its generic name is Diphenhydramine. The dosage is 4mg/kg. Give this 3x a day. It will make your cat sleepy so you might want to cut it back a little until he gets used to it. Good luck.

Ciao, Karen