As an addict and cannabis user, I can tell you that the medical industry really has no idea what addiction is. As you say, it’s complicated, and looking only at brains, or any particular body part, can’t reveal the nuances of addiction. Medicine, especially western medicine, can’t treat it effectively because they don’t have a good definition of it. In my experience, once the medical industry has labeled one an “addict,” certain levers get pulled and buttons pressed as if it’s a monolithic disease, which is such a crock. From there, most doctors treat addicts with a cookie-cutter approach destined to mostly fail. My experience tells me that the cure to addiction is community, and western medicine doesn’t seem to be willing or able to go there. Having doctors and researchers tell me about my addiction is like having Helen Keller tell me about blue.