Our study aimed to analyse the relationship between the rs6265 polymorphism of the BDNF gene and addiction to psychoactive substances in patients starting addiction treatment for the first time and in patients with addiction relapse, as well as to analyse personality traits assessed using the NEO-FFI Inventory; anxiety measured using the STAI questionnaire; and finally, the interaction between rs6265 and personality traits and anxiety. The gene discussed is BDNF; the disease is Anxiety.