In addition to rat park[0], there's also been an amazing study wrt to Viet Nam vets[1]. Only 5% of soldiers relapsed to heroin use in the first year of returning home. Compared to a traditional 90% relapse rate when addicts treated in the US return to their homes.
"Two studies (1, 2) tried and failed to replicate the results. Another two (3, 4) tried and mostly succeeded. There’s some concern that the rat strain involved might have various substrains that the different experiments didn’t control for. But a result that can’t survive a change in rat substrains has pretty dismal prospects for applicability to humans."
Fair warning, this video is pop science and therefore prone to many of its pitfalls, but when viewed in context I find Kurzgesagt[0] did an nice summary of this addiction theory.
[0] https://en.wikipedia.org/wiki/Rat_Park
[1] https://www.npr.org/sections/health-shots/2015/01/05/3718949...