Lexapro (escitalopram) is an oral medication used primarily to treat major depressive disorder and generalized anxiety disorder. It is part of a a class of medications called selective serotonin reuptake inhibitors (SSRIs). It works by increasing the levels of serotonin in the brain, a neurotransmitter chemical that plays an important role in maintaining mood signals in the brain.

It is believed that a possible cause of depression is a low amount of the neurotransmitter serotonin. In the brain, the space between where two neurons meet to communicate is called a synapse, and the synapse is where serotonin is used to communicate between neurons. In depression, people may not have enough serotonin in their brain. Normally after a chemical message is sent between neurons, the serotonin is reabsorbed by the sending neuron (presynaptic neuron).

A SSRI will bind to the presynaptic neuron and prevent it from absorbing the serotonin, and leaving the neurotransmitter active in the synapse, and improving mood.