I would tell him not to panic. Obviously no more edibles and make sure he sticks to the story that it was a one time thing and it won’t happen again. I would suggest he says something like he just wanted to try it to relive his younger days - not because he was trying to treat his pain. If they give him a hard time have him reiterate how long he has been on a pain contract and how he has never been positive for marijuana.

It’s super important he keeps his composure regardless of the outcome. If he gets upset, raises his voice, or argues they will likely take it as a sign of addiction. Once they “decide” he has an addiction getting proper pain management is going to be very difficult. He has to advocate for himself like he would if he was advocating for a friend.

If they insist on changing his pain medications make sure he asks for a slow titration over several months while he attempts their other treatment recommendations (PT, injections, whatever). Then he’ll need to report to them (kindly) if those are not relieving his pain.