I have not used it but a friend of mine has.
She had an older cat who got sick - multiple problems. Then the cat started losing chunks of hair - she was going bald.

The vet said it was irreversible. My friend would not give up and she found Dream Coat on the web and gave it to her cat. Within weeks, the cat had a wonderful coat of fur again. So, there must be something good in if the vet said nothing could be done and a simple supplement did the trick.