Comorbid disorders such as anxiety disorders, ADHD and substance-related disorders are common in bipolar patients. Comorbidity impairs the functional capacity, quality of life and prognosis in these patients. Psychiatric drug treatments of comorbid disorders are challenging as they may induce rapid-cycling and mania, thus worsening the outcome. Generally, the therapeutic requirements of the most severe disorders, i.e. bipolar disorder, are prioritized. In some cases the drug treatments of comorbid disorders are justified only after optimizing the therapy of bipolar disorder.