Why does lexapro (escitalopram) cause tiredness?

Sleep & Mood: Lexapro (escitalopram) is an ssri that can be a very effective antidepressant. Like other ssris, however, Lexapro (escitalopram) does not aid sleep directly. In fact, its direct effects on sleep may make sleep less restful. This could leave you tired by day. Sleep, however, is also related to mood and depression, so Lexapro (escitalopram) often helps sleep indirectly by helping depression, more than it hurts sleep byits direct effects.