Major depressive disorder and bipolar disorder have a lot in common. Both are mood disorders, meaning they involve fluctuations in mood that can be totally unrelated to life events. Both involve depressive episodes, which are periods of low mood.

In fact, the only real difference between major depressive disorder and bipolar disorder is the presence of manic, or manic episodes, in bipolar disorder. But these very similar conditions need to be handled very differently.

Antidepressant medications, the primary treatment for major depressive disorder, are extremely dangerous for someone with bipolar disorder to take as they tend to make manic episodes worse.