Introduction: Cannabis sativa extract has been used as an herbal medicine since ancient times. It is one of the most researched extracts, especially among supportive treatments against cancer. Prostate cancer is one of the most frequently diagnosed cancer types in men worldwide and an estimated 288,300 new cases were diagnosed in 2023. Today, many advanced therapeutic approaches are used for prostate cancer, such as immunotherapy and chemotherapy, but acquired drug resistance, long-term drug usage and differentiation of cancer cells mostly restricted the efficiency of therapies. Therefore, it is thought that the use of natural products to overcome these limitations and improve the effectiveness of existing therapies may offer promising approaches. The present study focused on the investigation of the possible enhancer role of cannabidiol (CBD), which is a potent ingredient compound of Cannabis, on the chemotherapeutic agent etoposide in prostate cancer cells. Methods: Herein, we tested the potentiator role of CBD on etoposide in prostate cancer cells by testing the cytotoxic effect, morphological alterations, apoptotic effects, autophagy, unfolded protein response (UPR) signaling, endoplasmic reticulum-associated degradation mechanism (ERAD), angiogenic and androgenic factors, and epithelial–mesenchymal transition (EMT). In addition, we examined the combined treatment of CBD and etoposide on colonial growth, migrative, invasive capability, 3D tumor formation, and cellular senescence. Results: Our findings demonstrated that cotreatment of etoposide with CBD importantly suppressed autophagic flux and induced ERAD and UPR signaling in LNCaP cells. Also, CBD strongly enhanced the etoposide-mediated suppression of androgenic signaling, angiogenic factor VEGF-A, protooncogene c-Myc, EMT, and also induced apoptosis through activation caspase-3 and PARP-1. Moreover, coadministration markedly decreased tumorigenic properties, such as proliferative capacity, colonial growth, migration, and 3D tumor formation and also induced senescence. Altogether, our data revealed that CBD has a potent enhancer effect on etoposide-associated anticancer activities. Conclusion: The present study suggests that the use of CBD as a supportive therapy in existing chemotherapeutic approaches may be a promising option, but this effectiveness needs to be investigated on a large scale.