My son made crazy accusations against me to anyone that would listen to him - I was told by professionals that it is typical and it is a way of deflecting the problems off of himself. As long as there is no truth then he is most likely trying to make himself look better in the docs eyes by saying these things - it gives him an excuse for using.
What i had to do was just detach emotionally from my son and never ever let him see that his accusations hurt. I opened my home and myself up completely to the professionals working with him and became an open book - even so far as admitting things i had done wrong (which we've all done some things wrong) - and never being defensive when working with them. It hurts - I know i hurts but look at it as a symptom of the disease.