The simultaneous consumption and misuse of different drugs are increasing nowadays. Millions of adults report the use of MDMA, while tramadol and tapentadol are among the most prescribed opioids for pain management, with an increasing trend for their misuse and abuse over the last decades. The present work aims to evaluate the toxicological effects of the chronic exposure to tramadol and tapentadol, as well as from the simultaneous exposure to MDMA and these opioids, using an in vivo model. To this purpose, the project aims to analyse the biochemical and histological alterations deriving from the daily administration of 10, 25 and 50 mg/kg doses of tramadol and tapentadol for 2 weeks, in metabolizing (e.g., liver and kidney) and target organs (e.g., lung and brain). In parallel, similar parameters will be analysed following combined exposure to MDMA and tramadol or tapentadol. It is important to understand the molecular and biochemical alterations deriving from the simultaneous exposure to drugs, in order to recognize their adverse reactions. The results are expected to contribute to a more careful prescription of tramadol and tapentadol.