Which statement best differentiates Bipolar I disorder from Bipolar II disorder?

• A. Bipolar I requires manic episodes; Bipolar II involves hypomania and major depressive episodes without full mania.
• B. Bipolar II features rapid cycling more than four mood episodes per year.
• C. There is no difference; they are the same disorder.
• D. Bipolar I never experiences depressive episodes.

Answer: (A)

The key idea is how severe the mood episodes are. Bipolar I is defined by having at least one manic episode—an unmistakable period of abnormally elevated or irritable mood with high energy that lasts at least one week (or any duration if hospitalization is needed) and causes clear impairment. Bipolar II, on the other hand, involves hypomanic episodes (similar symptoms but milder, lasting at least four days and not causing marked impairment) plus episodes of major depression, and it never includes a full manic episode. So the statement that Bipolar I requires manic episodes while Bipolar II features hypomania with major depressive episodes and no full mania best differentiates them.

Brief clarifications: rapid cycling (four or more mood episodes in a year) can occur in either form, so it isn’t the defining difference. It’s also incorrect to say there’s no difference at all, and it’s false to claim Bipolar I never experiences depressive episodes.