Paroxetine has been characterized as a highly potent and selective 5-hydroxytryptamine (serotonin) reuptake inhibitor. This selectivity has been demonstrated not only for monoamine uptake mechanisms but also for neurotransmitter receptor systems. The pharmacokinetic studies indicate that paroxetine may be administered once a day, and that on this regimen steady state will be achieved in 7–14 days. Furthermore, studies indicate that the metabolites of paroxetine do not contribute to its clinical effects. This profile supports the evidence from clinical studies that paroxetine is an effective and well-tolerated antidepressant with substantial advantages over the tricyclic antidepressants and other selective serotonin reuptake inhibitors.