Ahhh, okay.
Every doctoral program should contain some training in substance use/addiction. Some more than others. Many programs allow you to "focus" your training. For instance, pretty much all of my research will involve various aspects of addiction, on topics ranging from policy, to treatment research, to cognitive processes in addiction, to the neurobiology of withdrawal. I suspect around 50% or more of my total clinical hours will also involve working with substance use disorders. You can further specialize in post-doc.
This is a pretty typical training model for doctoral programs, and most programs will have at least one person who specializes in the area so opportunities are plentiful.