Attention-deficit/hyperactivity disorder (ADHD) is a risk factor for the development of substance use disorder (SUD). Individuals with ADHD often experience an early onset of substance use and a rapid transition from initial use to addiction. Furthermore, individuals with both ADHD and SUD exhibit more complex and chronic substance use patterns, as well as a higher frequency of polysubstance use, compared to individuals with SUD without ADHD. In these cases, other psychiatric disorders are also more frequently observed, notably antisocial and borderline personality disorders, mood disorders, and anxiety disorders.