JAMA Psychiatry 73 (5): 456 - 64, 2016. doi: 10.1001 / jamapsychiatry.2016.0152 Key Points Depression is a common disorder that involves depressed mood and / or near-complete loss of interest or pleasure in activities that were previously enjoyed; somatic (eg, weight change, sleep disturbance) and cognitive manifestations (eg, difficulty concentrating) are common.