Primary Cause

• People with major depression are thought to carry genes that make them more prone to developing symptoms. Depression does tend to run in families.
  
  

Secondary Causes

• People carrying the genes develop symptoms after being exposed to events such as illness, trauma, job loss or grief. But some people can develop depression for seemingly no reason.
  
  

Time Frame

• It is normal to show depression symptoms after a difficult life circumstance. But, according to The Family Intervention Guide to Mental Illness, it is not normal for symptoms to last more than two months.
  
  

Gender

• The National Alliance for Mental Illness notes that for unknown reasons, women develop major depression twice as often as men.
  
  

Warning

• Antidepressants can work unpredictably in some patients, causing their symptoms to drastically worsen. They may need to try several medications to find the right one.