Attention deficit hyperactivity disorder (ADHD) is a chronic neurobehavioral disorder that is highly prevalent in children and adults. An increasing number of patients with ADHD are self-medicating with cannabis, despite a lack of evidence on efficacy and safety. This case report describes 3 males (ages 18, 22, and 23) who have integrated cannabis into their treatment regimen with positive results. Semistructured interviews conducted with the patients describe subjective improvements in symptoms and on quality of life. Improvements on validated rating scales conducted post-cannabis initiation, compared to pre-cannabis initiation obtained from the medical chart, corroborated their personal accounts. Scores on the PHQ-9 (measuring depression) improved by 8–22 points (30–81%), and the SCARED (measuring anxiety) ranged from 0 to 27 points (up to 33%). Improvements on the CEER-9 scale (measuring regulation) ranged from 2 to 7 points (22–78%), and the 9-item SNAP scale (measuring inattention) showed improvements of 2–8 points (7–30%). Mild adverse events including short-term memory problems, dry mouth, and sleepiness were reported. Blood samples were also collected from the patients to determine the plasma concentrations of the cannabinoids and relevant metabolites before and after a cannabis administration. After cannabis use, the plasma levels for CBD and THC ranged from 0 to 15.29 ng/mL and 1.32 to 13.76 ng/mL, respectively. Cannabinoids, however, were not detected prior to dosing, suggesting that cannabis played a complimentary role in the therapeutic regimen of these 3 patients. Clinical trials are recommended to confirm the efficacy of cannabis in the treatment of ADHD.