Major Depressive Disorder: What It Is and What It Does

Updated: Nov 13, 2019

Major Depressive Disorder affects 18M people in the U.S. in any given year and 300M worldwide.

Major Depressive Disorder (MDD), often called clinical depression or simply depression, "is one of the most debilitating conditions on [sic] the world, with severe depression rated in the same disability category as terminal stage cancer," according to Hope for Depression.


Try and remember that the next time it seems that someone with a depressive disorder is "just being lazy."


The exact root cause of MDD is not known, but simply put, it occurs when the brain produces too much cortisol (the body's main stress hormone) and cannot efficiently use its supply of serotonin (the "happiness" hormone). When the brain releases serotonin, it can essentially get "sucked back in" by the serotonin transporter, preventing most or all of the hormone from having its intended positive influence on our thoughts and moods. Together with an overabundance of cortisol, this creates feelings of sadness, worry and despair beyond the control of the person living with the condition.


Depressive disorders account for a whopping 99% of all mental illnesses, with psychotic disorders and Schizophrenia making up the other 1%. The "depression umbrella" (the group of illnesses that make up this category of conditions) includes such prevalent disorders as post-traumatic stress disorder (PTSD), postpartum depression (PPD), anxiety disorders and bipolar disorder (BPD) and does not always, but can lead to suicidal thoughts and tendencies.


Symptoms of MDD include:

  • Feelings of sadness, tearfulness, emptiness or hopelessness

  • Angry outbursts, irritability or frustration, even over small matters

  • Loss of interest or pleasure in most or all normal activities, su