I wish I had an answer for you. We've been dealing with "over-grooming" for the past 3 1/2-4 years, first with one cat, and then with both. We are currently feeding them a Limited Ingredient Diet with mixed results (have recently switched to a non-Rx LID food, and there's been an increase in over-grooming again, especially on the part of one of our cats--could be coincidental, so we are continuing along with the new food for now, and monitoring the situation/behavior).

If you haven't had your cat checked out by your vet, I would do that and try to rule out any medical causes for the hair loss. Blood-work can be done to rule out a medical issue and/or allergies, though in our case the allergy-testing didn't provide any concrete answers.

Good luck!

Allergy testing in cats is a near complete waste of time as the results are nearly impossible to interpret. Fur loss in cats can be allergies (most common cause) or if the skin is also damaged, a list of skin infections from bacterial and fungal to parasitic. Also hair loss can be due to hormonal problems, but these are rare in cats. And severe malnutrition... but most cats lose hair from excessive grooming and allergies. What is your cat allergic to? No telling usually. Food is about the cause 1/4 of the time... environmental allergies 3/4 of the time (fleas are included in this second category). If it is just fur loss, and no skin damage or excessive barfing of hairballs, often we do not specifically treat this as losing the fur rarely leads to a medical problem. But you can try fatty acids, antihistamines and food trials. Steroids are reserved for those cats with associated medical problems, too.

Have its T4 blood test. Could have a Thyroid issue.