Lexapro is prescribed for major depression--a persistently low mood that interferes with daily functioning. To be considered major, depression must occur nearly every day for at least two weeks, and must include at least five of the following symptoms: low mood, loss of interest in usual activities, significant change in weight or appetite, change in sleep patterns, agitation or lethargy, fatigue, feelings of guilt or worthlessness, slowed thinking or lack of concentration, and thoughts of suicide.