Updated project metadata. Patients with major depressive disorder (MDD) have a high relapse rate and first prescribed selective serotonin reuptake inhibitors (SSRIs). The selection process of an antidepressant agent is primarily guided by trial and error. If patients do not benefit from the initial course of antidepressant medication for at least 4-6 weeks, additional therapeutic strategies are required to gain remission, including switching within and between classes of antidepressants. In order to discovery SSRI-related plasma protein markers, we designed a retrospective study. In this study, four longitudinal plasma samples were collected from 10 patients during the 10-week drug reaction period after being diagnosed with depression, and more than a thousand plasma proteins were identified by highly sensitive nanoflow liquid chromatography-tandem mass spectrometry (LC−MS/MS).