Major Depressive Disorder vs. Sadness: Why Clinical Depression Symptoms Require Professional Help

But sadness, even intense sadness, isn't the same as major depressive disorder (MDD), also known as clinical depression. What Is Clinical Depression (Major Depressive Disorder)? The defining feature of clinical depression is that major depressive disorder symptoms persist for at least two weeks and significantly impair functioning. Major Depressive Disorder Symptoms: The Full PictureMajor depressive disorder symptoms extend far beyond sadness. People with clinical depression isolate themselves, skip work or school, neglect personal hygiene, and avoid activities they previously enjoyed.