I'm reading Kent Dunnington's excellent book Addiction and Virtue: Beyond the Models of Disease and Choice.  He questions whether it makes sense to treat addiction in medical terms, as a disease.  I'm finding this a helpful way into a Christian concept of freedom that's compatible with divine sovereignty.  This is from chapter 1. 

We can imagine [how defenders of the disease concept of addiction might explain that idea.] "Our argument is really quite simple.  Drug abuse leads to changes in the structure and function of the brain.  Changes in behavior that can be traced to changes in brain structure and function are involuntary.  Therefore, the behavior of persons with addictions is involuntary.  And therefore, addiction is more akin to a human disease than a type of human action."

     This is indeed a simple argument, but is it sound?  It looks valid, so we must ask if its premises are true.  The first premise seems beyond dispute: ample studies demonstrate that the abuse of drugs changes the structure and function of the brain.  The problem with the argument comes in the second premise, which claims that changes in behavior that can be traced to changes in brain structure and function are involuntary.  The premise is problematic because, if it were true, it would turn out that all sorts of activities that we consider voluntary are in fact in involuntary.  For instance, studies show that the brain structure and function of skilled musicians are transformed by years of practice.  But surely this does not entail that, at some point, skilled musicians cease to be voluntarily engaged in playing their instruments.  Surely it does not entail that playing the cello may cease to be something a cellist does and becomes something a cellist suffers, a kind of disease.