Comorbid Cannabis and Tobacco Use in Adolescents and Adults.

The prevalence of comorbid cannabis and tobacco use has been increasing among adolescents and adults and has been shown to be associated with a range of changes or deficits in physical, psychological and behavioral outcomes. Moreover, comorbid use has been shown to have a differential effect on the structure and function of the brain, especially as it relates to the reward circuitry and learning and memory. This interaction might be mediated by the involvement of the endocannabinoid system and alterations in dopamine signaling in regions associated with reward and cognitive functioning. While current findings demonstrate a differential effect of comorbid use on neurobiological and behavioral correlates compared with single substance use, additional studies are needed controlling for potential psychiatric comorbidities, age of onset of use and use of other substances. Understanding the neurobiological mechanisms associated with comorbid cannabis and tobacco use will be important in developing successful treatment outcomes in the future.