Fentanyl and its potent derivatives, acetylfentanyl and carfentanil, are increasingly detected in illicit drug markets and associated with fatal overdoses. Although their pharmacological and forensic relevance is well recognized, their toxicological profiles remain poorly characterized at the cellular and molecular levels. Given their hepatic metabolism and rapid distribution to the central nervous system (CNS), it is crucial to clarify their effects in representative models of metabolizing and target tissues. This project aims to characterize fentanyl-, acetylfentanyl- and carfentanil-induced toxicity in hepatic and CNS cell models. Cell viability, oxidative stress, mitochondrial dysfunction, cellular bioenergetics and cell death mechanisms will be evaluated. Geneexpression changes related to inflammation, oxidative stress, apoptosis, and metabolism will also be assessed to identify molecular pathways involved in their toxicity. The proposed in vitro strategy will contribute to a better understanding of the hepatic and neuronal toxicity of fentanyl and its derivatives and provide relevant mechanistic data to support toxicological risk assessment in clinical and forensic contexts.