“Plant cannabinoids, secondary metabolites of species belonging to the Cannabis genus, can mimic the endocannabinoids’ action and exert biological effects. Considering the contribution of the endocannabinoid system in cell cycle and apoptotic regulation, there is an interest in exploring the potential anti-cancer activities of natural and synthetic cannabinoids. Cannabidiol (CBD), an abundant plant cannabinoid, reveals a low affinity to cannabinoid receptors and, contrary to various cannabinoids, lacks psychoactive action. Here, we present the in vitro assessment of the pro-apoptototic potential of CBD-rich extracts of Cannabis sativa L. (eCBD) compared to purified CBD (pCBD). As demonstrated, both eCBD and pCBD decreased the viability of breast cancer cell line MDA-MB-231 and human prostate cancer cell line PC-3 in a concentration-dependent fashion. Endoplasmic reticulum stress-related apoptosis and morphological changes were induced only in low-serum conditions. Moreover, the effects of eCDB and pCDB were also assessed in non-malignant cell lines (MCF-10A and PNT2) with no alterations of viability noted, ultimately suggesting a selective action of CBD in tumor cells. The results suggest the possible involvement of reactive oxygen species in the response mechanism to eCBD and pCBD, but no clear pattern was observed. We also demonstrated significant changes in gene expression involved in apoptosis and cell cycle control upon extract treatment. Altogether, our study shows the potential of eCBD and pCBD as novel pro-apoptototic agents that can be considered promising in future preclinical and clinical testing.”