Hi...my Son Is 31 And Has A Bi Polar Diagnosis

Hi...my son is 31 and has a bi polar diagnosis and takes lithium. He also has Crohn's and is taking infusions of the latest drug - has had all the big ones in the past and they only work for a while. He has new insurance and will be looking for new Drs in Boulder, CO area. He is working with a nutrition Dr now and seeing small improvement in Crohns symptoms.
Is it possible to stop taking lithium gradually to see if he really needs it anymore? His last episode was 5 years ago.