Substance use in adolescents affects brain development and can influence health in adulthood. The substances most commonly used by adolescents are alcohol, cannabis, and tobacco. Adolescent alcohol use has been shown to inhibit and alter normal brain development, and has been associated with alcohol use disorder and other mental disorders in adulthood. Cannabis use during adolescence has been associated with adverse mental health outcomes. Adolescents may incorrectly assume that the negative health effects of smoking will not affect them. Electronic nicotine delivery systems, such as e-cigarettes, for vaping may be used to inhale nicotine, cannabis, or both. Strong family relationships and parental monitoring are protective factors against substance use. Screening at every preventive services visit is an essential element of adolescent care. The evidence-based Screening, Brief Intervention, and Referral to Treatment (SBIRT) strategy has been shown to decrease substance use and its adverse effects in adolescents. On societal and community levels, family physicians have numerous opportunities to advocate for adolescent well-being and prevention of substance use. The American Academy of Family Physicians (AAFP) recommends that family physicians advocate for legislation and governmental policies that facilitate the prevention, diagnosis, and treatment of substance use.

Case 3. AS is a 16-year-old adolescent boy (pronouns: he/him) who comes to your office for a medical evaluation after being suspended from school for truancy and possession of marijuana on campus. He reports that he began vaping 2 years ago and then started dabbing cannabis extract once or twice a week with friends a few months ago. He says he initially started using cannabis for fun, but he now uses it to help him relax and fall asleep at night. He does not perceive cannabis as harmful, and says, “Well, it’s legal, so it’s got to be pretty safe.”

Epidemiology and Mechanisms

The substances most commonly used by adolescents are alcohol, cannabis, and tobacco (Table 8).¹⁰⁴ Discussions of prescription drug abuse, opioid use disorders and their management, and use of other substances are outside the scope of this edition.

The adolescent brain undergoes enormous changes during growth and maturation, which can lead to an increased risk of substance use disorders.¹⁰⁵ Through synaptic pruning, the neuronal connections and pathways that are used most often become strengthened, and the unused or less used pathways atrophy. Use of alcohol, cannabis, and nicotine have been shown to alter the developing brain and synaptic pruning, particularly in the prefrontal cortex and hippocampus.^{106,107,108,109,110,111}