BACKGROUNDMost antidepressants with similar pharmacological characteristics exhibit comparable therapeutic efficacy but differ in side effects. Therefore, we used a retrospective design to compare biochemical changes induced by six antidepressants and identify differences among them.METHODSCase records from 1706 hospitalized patients with major depressive disorder (MDD) receiving antidepressant monotherapy were divided into six groups based on the specific antidepressants used: paroxetine, sertraline, fluoxetine, escitalopram, venlafaxine, and duloxetine. Electrolytes, hepatic and renal functions, body weight, and glycolipid metabolism were assessed at baseline and 2 weeks post-antidepressant initiation. Paired analysis was used for comparing the changes prior to and after administration within each group, and analysis of covariance was used for evaluating the distinctions among the six groups.RESULTSAfter 2 weeks of treatment, significant decreases in serum sodium and chloride levels were observed with venlafaxine, duloxetine, and fluoxetine, while potassium, phosphorus, and carbon dioxide concentrations tended to increase across all six antidepressants. In terms of hepatic indicators, these antidepressants significantly elevated alanine aminotransferase (ALT), aspartate aminotransferase (AST), and γ-glutamyl transpeptidase (GGT) levels, with duloxetine showing the most pronounced changes from baseline, while decreasing total and direct bilirubin. Sertraline effectively reduced uric acid, although changes in renal indicators were mild with other antidepressants. Notably, these antidepressants were associated with an unfavorable lipid profile, particularly elevated triglycerides and cholesterol, but they lowered blood glucose during the acute phase.LIMITATIONResidual confounding may indirectly influence the retrospective outcomes.CONCLUSIONEarly biochemical changes can distinguish differences among antidepressants and guide individualized medication.