My cat, Charlie, did this all her life - she was diagnosed obsessive/compulsive too - in the end we just had to live with it but on the plus side it did her no lasting harm. One point though - we used to think it must have been something we were doing wrong. However, we have two new cats now (sadly, Charlie dies last year for unrelated reasons), and these are both fine with a full complement of fur. My advice - treatments are often stressful for the cat - if you've tried the usual treatments with no success, you may just have to live with a bald cat!