Drug induced Psychosis. Should be done?

My brother has been living alone in Paris for last 2 years and didn't have any close friends. He always had performance pressure as a lot of money was spent on his education and wasn't performing too good which later turned into depression. He himself admit that he had suicidal tendencies at sometime. He started cannabis misuse to come out of his depression, which probably helped him come out of depression. About a month back he told us that our dead grandfather spirit comes and talk to him listening to which we immediately called him back to India. His symptoms worsen with time and last week we realized that he needs medical help urgently. Me and my dad went to a Dr. to understand his situation as he was and still is too reluctant to come with us. Dr. diagnosed him with Psychosis and we could relate all the symptoms with his present condition. It has been a week that we've been giving him the prescribed medicines but we still don't see any significant improvement. What should be done?