Feather plucking can become a habit if it is not treated in time. Usually there is more than one underlying cause for the bird's feather plucking, and you need to explore and treat all of them, with your veterinarian's help.
It is also important to keep your bird busy with toys, use behavioral therapy or change its environment to reduce isolation. Omega fatty acids, when added to the diet, has also proved successful in reducing feather plucking.
One treatment alone cannot fully remedy feather plucking; it has to be a combination of different therapies. Also, medical treatment which is not followed by behavioral therapy, will often cause your bird to pluck its feathers once again.