Drug repurposing in oncology promises a high impact on many patients through its ability to provide access to novel, fast-tracked treatments. Previous studies have demonstrated that depression may influence tumor progression. Anti-proliferative activity of certain antidepressants, mainly selective serotonin reuptake inhibitors (SSRIs), are reported in the literature. This study was conducted to repurpose selective serotonin reuptake inhibitors (SSRIs) in treating breast cancers, and it merits the pursuit of drug repositioning in oncology. Changes in cell morphology were studied using DAPI staining, and the Annexin V/PI method was employed for apoptotic analysis. The expression of specific genes involved in cancer progression was also analyzed via RT-PCR. Caspase-3 activation was observed through fluorometric assay. We have identified that sertraline hydrochloride most effectively inhibited the growth of breast cancer cell cells in vitro. Preliminary mechanistic studies demonstrated that the cytotoxicity of sertraline hydrochloride was possibly through the induction of apoptosis, as inferred from enhanced nuclear fragmentation, flow cytometric data, and caspase-3/7 activation. Gene expression analysis also showed an increased expression of proapoptotic Bax and a slight decrease in oncogene c-myc in the presence of sertraline hydrochloride. In conclusion, our data suggest that sertraline hydrochloride, an antidepressant, can potentially be used for the treatment of breast cancer.