Fluoxetine is an inhibitor of serotonin reuptake to incerase the level of serotonin in synapse cleft. Axons of serotonergic neurons are widely distrubuted in the entire cerebral brain, such that fluoxetine is acting onto numerous cells in the brain. Moreover, serotonin is one of neurotransmitters that maintain wakefulness through the ascending activating system in the brain stem. Fluoxetine may raise wakeful state instead of specifically improving low mood state in major depression.
Prozac (fluoxetine) is selective serotonin reuptake inhibitor (SSRI). It works by blocking the absorption of the neurotransmitter serotonin in the brain. It also results in more neurons being present in a region of the brain called the "dentate gyrus," part of the hippocampal formation.