Drug repurposing has been proved to be an effective strategy to meet the urgent need for novel anticancer agents for multiple myeloma (MM) treatment. In this work, we aimed to investigate the anticancer effect and mechanism of tricyclic antidepressant nortriptyline (NTP) on the U266 MM cell line. The in vitro inhibitory effect of NTP at various doses and time points was studied. The combination potential of cisplatin-NTP was also investigated. Cell cycle analysis and three flow cytometric apoptosis assays were performed. NTP showed dose- and time-dependent inhibitory effects on the U266 MM cell line. NTP had greater inhibitory effect than cisplatin (IC50 26 mu M vs. 40 mu M). The cisplatin-NTP combination is antagonistic. In addition to G2/M phase cell cycle arrest, NIP induced apoptosis as indicated by mitochondrial membrane potential and caspase-3 and annexin V assays. NIP has inhibitory and apoptotic effects on U266 MM cells. The cisplatin-NTP combination indicated strong antagonism, which may have significant clinical relevance since antidepressants are commonly employed in adjuvant therapy for cancer patients. Based on these findings, the therapeutic potential of NTP for MM treatment should be investigated with in-depth mechanistic studies and in vivo experiments.