The COGA study supports the conclusion of other investigators (Merikangas and Gelernter 1990; Merikangas et al. 1994) that alcoholism and depression tend to occur together and that comorbid alcoholism tends to aggregate in the relatives of probands with both disorders. The definition of depression in this analysis includes both major depression (i.e., primary depression) and depressive syndrome, which may be caused by alcohol and other drug use (i.e., secondary depression). However, primary and secondary depressive syndromes may not truly be distinct. Many people with alcohol problems spend a substantial portion of their lives drinking and thus have less opportunity to demonstrate independent episodes of depression. An alcoholic with true vulnerability for depression may, by the natural course of the two illnesses, have no demonstrably independent episodes.
