He could try GABA, an amino acid. It would help with his mood swings and anxiety, too. If you think he has bipolar disorder, you might be able to find some lithium aspartate in your health food store; it might help, even if he doesn't have bipolar. Both of these are calming, probably good for A type personality.
I had the same addiction, and am very sensitive (artistic, too), also, more B type. When I quit, I started taking Relora (for depression), which has helped tremendously. I also take Rhodiola Rosea, which helps anxiety.
I've read that marijuana makes the body acidic, so the more fruits and veggies he can eat, the better.
You're a good brother to care.
Editing to add: he'll need something to help him sleep, too, as he will be producing less melatonin now. Taurine is another amino mood stabilizer and helps sleep. Also Epsom Salts baths can help.
I hope he is able to get off the pharmacy drugs soon, too - very much agree with you about that.