Its hard to watch an addict who has blinkers on in some respects, Im going to make an assumption, that when he was seeking his "high", that was all he could think about as he built up to taking them, how great it was going to be, how good it would make him feel (probably invincible), that's the addict brain in action hence my description of blinkers.
Seeking the high he rationalised that it wasnt illegal or alcoholic, so it was going to be just "this one time", This was prescription drugs but to get the sought after high, he was using them not as prescribed. So same as illegal, as when he would run out of the prescription, if it had given the high, I am willing to guess he would "lose prescriptions", going on holiday etc to try and get replacements,
Meanwhile his body esp his brain will be "all over the place" with neurotransmitters which influence mood etc. So with the "seeking the high dose being a lot", he was probably taken off them for a couple of days by which point depends on the medication he may have started to feel withdrawal symptoms and a circle can go from there.
He may not be linking in and engaging with AA because he knows he isn't following his steps and that even for theory sake as a step backwards for now, recovery isn't a straight line. There are backward steps, side steps and the glorious forward steps, there is no finish line either.
Can your GP refer him to the local addiction services - for example, my area is overseen by a psychiatrist team who call the shots, the nurse practitioners review people monthly more often if needed.
If he is struggling and missing the effects of alcohol, drugs/meds to produce that high, they can prescribe different antidepressants that will dampen that down. There are alternative therapies as well - a harm reduction agency close to me offers counselling (not alternative but just came to mind) and auricular acupuncture (it hits the areas in the ear that correspond to addiction centres in the brain)
How do I know this? I spent 18m working in a rehab centre as a support worker, I then moved to a mh support job where I worked part office based, part resource centre based and part street-based, my service users often had multiple difficulties inc addiction to various substances.
A couple of years in before I became chronically ill and was medically retired.
I met my partner, who on our first date dropped the bombshell that he had a past and was in recovery, he had been addicted to cannabis, later opium by buying flowers a lot, codeine, benzodiazepines, poppers, uppers, downers and a lot more, the previous year he managed to engage for 2 weeks with local addiction unit while he detoxed and change of lifestyle, he has now been clean for over 12 years (bar one relapse) and is still in recovery, he sees the NP/addiction psych every month and has to provide a urine test under supervision each time.
Once the urine is shown to be clear, only then will the chemist give him his dose of Subutex and that's a supervised dose, so they have to check its dissolved and then his take-home doses. It is only this year he has gone to once a week pick up, at the beginning it was daily, bar Sundays.
I've been with him over 10 years now, he had one bad relapse back about 5 years ago, he started injecting his prescribed medication, each time he did it, it was the last time, he had a bad day, he needed to get the best out of the dose. I called intervention, as I blew up at him and he had picked up his phone to call his parents to come and collect him. I grabbed landline and asked them to come in, the secret was out. He was stunned they knew and that we had all been waiting for rock bottom to hit, they informed the addiction service who stepped in with intensive support and more tests, tighter controls. He hated me for several days but I think his mum told him to cop himself on, none of us was going to watch him destroy himself bit by bit without intervening and that enabling him wasnt going to help him. No sympathy at all for him and with tough love, he has been on the straight and narrow since.
Use all avenues you have and Al-Anon for support.