Background <p>Gastric cancer is a highly heterogeneous and aggressive disease with limited treatment options, necessitating innovative therapeutic strategies. Drug repurposing, a cost-effective approach, offers opportunities to identify new applications for existing medications. This study systematically investigated the apoptotic effects of serotonergic drugs on MKN-45 gastric cancer cells, providing a novel perspective on serotonin signaling in cancer therapy.</p> Methods and results <p>MKN-45 cells were treated with concentrations of Tropisetron, Imipramine, Ketanserin, Citalopram, and Cyproheptadine. The IC50 values were determined using an MTT assay, while acridine orange/ethidium bromide staining and Annexin V/PI flow cytometry assessed apoptotic activity. Gene expression related to serotonin receptors (<i>HTR2A</i>,<i> HTR2B</i>,<i> HTR3A</i>), Serotonin transporter (<i>SLC6A4</i>), apoptosis (<i>Bcl-2</i>,<i> Bax</i>), and proliferation (<i>PCNA</i>) was evaluated via real-time PCR. Tropisetron, Imipramine, Ketanserin, and Cyproheptadine demonstrated statistically significant apoptotic induction compared to untreated cells. These treatments significantly reduced anti-apoptotic <i>Bcl-2</i> and <i>PCNA</i>, proliferation marker, expression, while pro-apoptotic <i>Bax</i> expression was markedly elevated (<i>p</i> &lt; 0.05).</p> Conclusions <p>This study highlights the potential of Tropisetron, Imipramine, Ketanserin, and Cyproheptadine as repurposed drugs for gastric cancer therapy, with Tropisetron and Imipramine showing particularly promising apoptotic effects. These findings pave the way for further preclinical and clinical investigations, offering a foundation for personalized therapeutic strategies in gastric cancer management.</p>