In contrast to bipolar I patients, comorbid alcohol dependence may have little influence on the course of bipolar disorder in bipolar II individuals in the current sample. Except for severity of symptoms during their most severe depressive episodes, the course of bipolar II disorder is very similar in both groups with and without comorbid alcohol dependence. Furthermore, no significant differences were found in alcohol dependence and bipolar characteristics between the two groups of bipolar I and II subjects during the 5 years of follow-up were found. These results confirm the findings from the baseline analysis. While only few studies considered bipolar II subjects in their studies on comorbid alcohol use disorders in bipolar individuals, a previous investigation reported almost equal rates of alcohol dependence in bipolar II compared to bipolar I individuals (30). In comparison, a more recent prospective study found more than twice the rate of alcohol dependence in bipolar II vs. I patients (31), while other samples did not detect any influence of alcohol use on mood symptoms or social functioning in bipolar II individuals too (17).
