Everything we do impacts brain chemistry. By extension, non-pharmaceutical interventions can change brain chemistry. The mistake is in the notion that said chem

Everything we do impacts brain chemistry. By extension, non-pharmaceutical interventions can change brain chemistry. The mistake is in the notion that said chemistry is invariably statically a-priori "wrong" in every single case people get addicted or depressed (it becomes as such), and acting as though addiction in itself is only relegated to the realm of the abnormal, that "normal" human beings can't be addicted. And yes, notwithstanding that there are cases where people are, owing to genetics, more susceptible to x/y/z, or where interventions can be insufficient. But that's the first line of defense, and should be. There's a lot of anecdotes surrounding this but a popular one is rate of morphine abuse during and after the Vietnam war. The rates plummeted. A really good book on the topic of addiction is the Biology of Desire by Marc Lewis. I would also caution against any conflation of environmental and behavioral intervention as "willpower". These are not the same things (you didn't say they are, but you didn't give any credence to intervention). Willpower may be highly overrated, but ultimately, you can't "force" someone to rehabilitate in any way shape or form. They have to want to, they have to make the choice, and commit. As for therapy/rehab, some of these have been thoroughly studied. Interventions help (and therapy such as CBT or 3rd-wave CBT), considerably.