Key Takeaways: ADHD is linked to higher substance use disorder prevalence, with men showing higher rates than women for most substances. Data from Norwegian registries revealed significant sex differences in SUD prevalence, especially for cannabis, sedatives, cocaine, and amphetamines. Comorbid psychiatric disorders, particularly schizophrenia/psychosis, exacerbate SUD prevalence in individuals with ADHD. The study emphasizes the importance of early intervention for young individuals with ADHD to prevent comorbid disorders.