There is substantial documentation in medical literature about the positive concordance between substance abuse and other hereditary mental disorders such as schizophrenia, depression and bipolarity. Whether it is a type of personality disorder (untreatable by medications), a form of dissociative or mood disorders (largely treatable by medications) or otherwise remains a subject of intense research and debate.
I have treated many different types of substance abusers, from the garden-variety alcoholics all the way to highly secretive opiate addicts and they all have one thing in common--an addictive personality. It is difficult to discern the features of an addictive personality without substantial training and experience in the field, but those features can and do exist. When you are told that you have an addictive personality, you really have to watch your lifestyle carefully.
Like many other substance abusers, Michael seems to have gone through turbulent ups and downs, much like a bipolar patient. It is sad to see, but nonetheless, he chose his path and now must live with the ruins.