What defines bipolar I disorder?

Bipolar I disorder is defined by the presence of at least one manic episode. This manic episode is characterized by an elevated or irritable mood, increased activity or energy, and other related symptoms such as grandiosity, decreased need for sleep, racing thoughts, or distractibility that last for at least one week (or any duration if hospitalization is necessary). While individuals with bipolar I disorder may also experience depressive episodes, these are not required for the diagnosis. The essential feature of bipolar I disorder is the experience of these manic episodes, which can lead to significant functional impairment or require hospitalization to prevent harm. Thus, the defining characteristic is the occurrence of at least one manic episode.