My 39 Year Old Son Struggles With A Meth Addiction.

My 39 year old son struggles with a meth addiction. He recently relapsed after 10 years of sobriety. Three month later he was diagnosed with non-Hodgkin lymphoma and has had 2 rounds of 6 (3 weeks apart) of R-Chop chemotherapy. The prednisone part of the treatment is 100mg once a day for 5 days. No tapering off, he has to just stop. On the 5 - 6 th day, his personality changes drastically and he is craving his meth. It is heartbreaking to watch the prednisone undo what he struggles with the other 2 weeks of the treatment. For about a week, he is so strung out on the prednisone - I am sure he goes to do the meth, but I have no proof. Then he begins to crash and knows he can't test positive on his drug tests so he stops - and can do that, because the prdnisone is out of his system. This is a horrifying roller coaster for all of us. I am afraid to talk to his doctor. She knows about his previous meth use and has told him if he tests positive she will cut off his treatment. Is it possible to alter the amount of prednisone in his treatment?