Long-term oral fluoxetine leads to reduced male reproductive function in mice and gradual recovery after discontinuation

Fluoxetine, a widely used selective serotonin reuptake inhibitor (SSRI), is highly effective in treating psychiatric disorders such as depression. Recently, its potential negative impact on male reproductive function has recently raised concerns, but it remains unknown whether testicular damage from long-term fluoxetine exposure can recover after stopping the drug. In this study, male C57BL/6 mice were divided into control (saline) and treatment (fluoxetine, 20 mg/kg.d) groups, administered orally for 4 weeks. This duration and dosage have been proven to demonstrate significant antidepressant effects in mice. Fertility assessments and euthanasia was then performed at three time points: immediately after treatment cessation, 4 weeks post-discontinuation, and 8 weeks post-discontinuation (n = 8). Results found that following long-term fluoxetine administration, male mice exhibited significantly reduced mating and fertility indices, decreased sperm count and motility, and increased sperm deformities compared to the control group. Testicular histology showed immature germ cells within the seminiferous tubule lumens, along with significantly reduced seminiferous epithelial thickness, seminiferous tubule diameter, and Johnsen score. Ki67 (proliferation marker) expression decreased, while Caspase3 (apoptosis marker) increased. By 4 weeks post-discontinuation, Ki67 and Caspase3 levels in the fluoxetine-treated group returned to control levels, with partial recovery in other parameters. By 8 weeks, all measured parameters had largely normalized, indicating significant recovery in reproductive function. These findings provided novel insights into fluoxetine's reproductive toxicity and were crucial for assessing its clinical safety in drug evaluations.