What are the difference between manic depressive disorder and major depression?

Bipolar vs. major: The key difference between manic-depressive (a.K.A., bipolar) and major depression are the swings in mood. Depression can include anxiety and irritability but not mania (i.e., pressured thoughts & speech, impulsivity, low need for sleep, highly focused behaviors). There are forms of bipolar without mania. If you're worried about yourself, friend or loved one, talk with your doctor. Reach out!

Dr Pappas and another doctor agreed

Mania: People who suffer from manic depression ("bipolar") have two poles of extreme mood--both depression (low) and mania (high) as colleagues have described. It's important to realize that with just episodes of depression, it is not certain whether the depression is "unipolar" or part of "bipolar". Once one has a manic episode, bipolar is confirmed, even if the depression has not yet appeared.