There's quite a bit of research on the role of dopamine in addiction, and it seems reality is very complex,
https://www.theguardian.com/science/...e-unsexy-truth http://www.nature.com/nrn/journal/v1...l/nrn3939.html The addicted brain - Harvard Health
Addictive drugs all affect neurotransmitter processes in the brain, but different ones in different ways, and dopamine is involved in many areas of brain function that don't have anything to do with addiction. So, there don't seem to be any simple chemical explanations for addiction.