This study aimed to investigate the efficacy of DìRelaxTM, a nutraceutical formulated to reduce anxiety in dogs. The CBARQ questionnaire, some clinical investigations, and the impossible task test were performed in dogs before and after the treatment. Results showed an ameliorative effect on the performances of treated dogs during the solvable phases, with a significant decrease of the time needed to solve the task. No behavioral difference was found between treated and untreated anxious dogs during the unsolvable phase. According to the results from the C-BARQ questionnaire, some of the behaviors appear improved. In general, this study suggests that DiRelaxTM can be safely administered with no adverse effects and can exercise a beneficial effect on anxious dogs by enhancing their cognitive abilities.