Depression is not simply a state of ‘mood’. It becomes a part of life of the depressed person. Slowed speed of thought, inability to make brisk decisions, not wanting to talk to people; these are the initial presenting features of pathological depression (making it different from ‘just a bad mood’). Depression may mask itself and present contrarily to what is expected of it. Sometimes one may experience ‘atypical’ symptoms like overeating, excessive sleeping, anger (instead of sadness), restlessness, agitation; all of which never arouse the suspicion of ‘depression’. Mood changes during menstruation, chocolate craving, anger outbursts, seasonal mood switches are all masks that depression garbs itself in. It may occur in bouts for short periods of time (recurrent brief depression), may be seen monthly in females prior to the menses (pre-menstrual dysphoria), may follow a seasonal pattern of coming up in the summer or winter months (seasonal depression), or may be continuous and last for years together (chronic depression). Knowing this helps in understanding trial protocols.

Measurement of social behavior and subjective feelings has shown that depression is one of the most disabling and distressing medical illnesses, causing significant disability. The continuous mental pain seriously influences the quality of life and the person rightly feels that life is really not worth living. The risk for suicide is the highest in depression compared to all other disorders. The quality of life is an indicator of therapeutic response. These variables are typically assessed as per protocol. A detailed understanding of the same helps trial staff offer their best for optimal functioning of the trial.