Attention-deficit/hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder in children and adults. In the substance use disorders (SUDs) population, ADHD prevalence reaches 23.1%, leading to more severe substance abuse progression and reduced treatment effectiveness. Cannabis is the most common illicit drug used among the ADHD population. The increasing popularity of medical marijuana (MM) has raised concerns about its potential impact on neurocognitive functions, particularly in adolescents. Persistent cannabis use can cause permanent changes in brain structures and circuits. This review aims to overview the comorbidity of ADHD and SUDs, focusing on cannabis use disorders. Theoretical models of the etiologies of ADHD and SUDs were investigated to establish a framework for analyzing their underlying neurocognitive mechanisms. The reward and motivational brain circuitries involving the default-mode network and the endocannabinoid system were emphasized. The high prevalence of SUDs in the ADHD population has ramifications, including earlier age of onset, self-medication, and reduced performance in various domains. Cannabis use disorders are particularly significant due to the increasingly widespread use of cannabis and its perceived safety. The review highlights the lack of theoretical background on the therapeutic properties of medicinal cannabis, criticizing its speculated applications in the ADHD population. This article reviews the current understanding of the association between ADHD and cannabis use, emphasizing the need for further research and a cautious approach to MM's potential therapeutic applications.