I think that substance abuse is a symptom of a deeper disease. It is a disease of denial, and unwillingness to introspect, integrate, take ownership, change, and grow. It is a stuckness that medicates, projects, denies, and attacks in order to maintain and perpetuate itself.
On this side, the codependent, or more accurately the codenier, denies themselves also, and their needs, and feelings, and works to support the narcissist in their self-denial.
Narcissism and codependence / anti-narcissism are just two parts of the same disease. Alcoholism is just one of several symptoms of the disease.