The relationship between attention deficit hyperactivity disorder (ADHD) and addiction represents a major field of interest for clinicians. Numerous studies have found that ADHD sufferers are over-represented among alcohol abusers or addicts (35–70%) and among drug abusers or addicts (15–25%). Furthermore, it has been found that 17–45% of ADHD patients are alcohol addicts and 9–30% are illicit drug addicts. In adults with ADHD, substance use disorder (SUD) is often more severe and has an earlier onset than in the general adult population. Even though the epidemiological data for most European countries are patchy, the issue of SUD in ADHD sufferers remains a valid one.