Major Depressive Disorder (MDD) is a common psychiatric disease, affecting over 350 million people worldwide.1 According to the Word Health Organization (WHO), about 1 in 20 people experiences a Major Depressive Episode (MDE) each year.1 The point prevalence rate is 4.2% in China, which means more than 54 million people are suffering from depression.2 Depression is a heterogeneous disease, comprising a broad range of symptoms, including mood, physical and cognitive symptoms. Depression does not only lead to significant mental and physical disability, but also places a great economic burden on society.1 (December 2016)