These illnesses can be medical or psychiatric conditions, as well as drug use disorders, including alcoholism. Comorbid illnesses may occur simultaneously or sequentially. The fact that two illnesses are comorbid, however, does not necessarily imply that one is the cause of the other, even if one occurs first. An understanding of comorbidity is essential in developing effective treatment and prevention efforts. For example, since alcoholism causes liver disease, measures to decrease alcohol consumption will help reduce the incidence of liver disease.
Alcoholism can cause various medical and psychiatric conditions or increase their severity.
Comorbid disorders might cause alcoholism or increase its severity. Both alcoholism and the comorbid disorder may be caused, separately, by some third condition. Most studies of comorbidity are based on clinical samples. This trend may be countered to some extent by the reluctance of some alcoholism treatment centers to admit persons exhibiting serious psychiatric problems. Additional methodological difficulties complicate both clinical and general population investigations.