More Reasons for Concern About Adolescent Cannabis Use

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Cannabis is a widely used drug of abuse in adolescents. With legalization of marijuana, adolescent cannabis use may increase substantially. Clinicians are often faced with a depressed, anxious, or suicidal adolescent who uses cannabis to self-medicate symptoms and is unwilling to stop using cannabis. Several recent studies provide further evidence of the adverse mental health consequences of cannabis use in adolescents.

Depression, anxiety, suicidality

A systematic review and meta-analysis examined the risk of adolescent cannabis use in the development of major depression, anxiety, and suicidal behavior.¹ The analysis included longitudinal and prospective studies of cannabis use in adolescents aged younger than 18 years who were then assessed in young adulthood (aged 18-32 years). Eleven studies for a total sample of 23,317 adolescent cannabis users were included in the analysis.

The risk of depression (odds ratio [OR] = 1.4), suicidal ideation (OR = 1.5), and suicide attempt (OR = 3.5) in young adulthood was significantly higher in adolescent cannabis users than in nonusers; a significantly increased risk was not found for the development of anxiety disorders (odds ratio = 1.2). It is important to note that the increased risk of depression and suicidal behavior in young adulthood was present even in the absence of a premorbid psychiatric condition. Based on this study, the researchers concluded that the estimated population attributable risk of depression from cannabis use is 7.2% in adolescents; approximately 413,326 cases of adolescent depression are potentially attributable to cannabis use.

Age, cannabis use frequency, and mental health problems

The effects of age on cannabis use frequency and cannabis use disorder on psychotic, depression, and anxiety symptoms in adolescents and adults were evaluated by Leadbeater and colleagues.² A randomly recruited sample of 662 adolescents aged 12 to 18 years was assessed over a 10-year period.

More frequent cannabis use was significantly associated with more depressive symptoms from ages 16 to 19 and after age 25. Furthermore, cannabis use was significantly associated with psychotic symptoms after age 22. There was no association between frequency of cannabis use and anxiety symptoms in the study sample. With regard to cannabis use disorder, there was an association with higher depressive symptoms at ages 19 to 20 and after age 25; psychotic symptoms after age 23 were associated with adolescent cannabis use disorder. Cannabis use disorder was also associated with higher anxiety symptoms at ages 26 to 27.

Adolescent cognitive development

Morin and colleagues³ examined the relationship between cannabis use and cognitive development in adolescents. The study sample included 3826 seventh graders (mean age, 12.7 years) from 31 schools in the Montreal area. These youth were assessed annually for 4 years (grades 7-10) on cannabis use, alcohol use, and cognitive functioning, including recall memory, perceptual reasoning, inhibition, and working memory. The assessments were completed via a confidential annual web-based survey during class time to assess cognition and substance use.

Adolescent cannabis and alcohol use were associated with lower working memory, perceptual reasoning, and inhibitory control. Of particular concern, cannabis use showed neuroplastic (concurrent effect) and neurotoxic (lasting effect) of cannabis, which was not found for alcohol use. For example, when adolescent cannabis use increased in frequency in a given year, there was a reduction in delayed recall memory and perceptual reasoning in that same year.

Cannabis use in a given year was also associated with impaired inhibitory control and working memory a year later. These findings are particularly worrisome given that cannabis use in this sample was low and infrequent, yet cognitive changes were detected with small increases in cannabis use.

Decreased threat responsiveness as a function of cannabis use disorder has been reported in adolescents.⁴ Eighty-seven adolescents with cannabis use disorder and/or alcohol use disorder were scanned with fMRI during a looming threat task. During this task, adolescents were shown images of threatening or neutral human faces or animals that appeared to be looming (increasing size over time) or receding (decreasing size over time).

Adolescents with higher severity of cannabis use disorder symptoms showed decreased response to looming stimuli within the rostral frontal and fusiform gyrus and amygdala. There were no associations with alcohol use disorder symptoms. The researchers speculate that decreased threat responsiveness may be a neurotoxic effect of cannabis abuse and related to conduct problems (less concern about negative consequences) associated with cannabis use disorder.

Mental health effects and increasing cannabis potency

The potency of cannabis with rising concentration of delta(9)tetrahydrocannabinol (THC) has been increasing over the past few decades. Wilson and colleagues⁵ reviewed the effects of increasing cannabis potency on adolescent health.

High-potency cannabis was associated with five times higher probability of having a diagnosis of a psychotic disorder compared with cannabis nonusers. Increased risk of relapse following first episode of psychosis was associated with frequent use of high-potency cannabis. In cross-sectional studies, high-potency cannabis use was associated with depression and anxiety in adolescent cannabis users. These findings are concerning because adolescents typically have little information about the potency of cannabis that they are using.

Clinical implications

These recent studies add significantly to the evidence that cannabis use in adolescents has adverse effects on mental health with risk for depression, psychosis, and cognitive impairment, especially inhibitory control. Adolescents and their parents need to be informed about the adverse consequences of cannabis use, whether the adolescent is or isn’t currently using substances. Many psychiatric disorders increase the risk for cannabis use and conversely frequent cannabis use, especially higher potency cannabis, increases the likelihood of psychiatric disorders. With pending legalization of marijuana and increased access for adolescents, the public needs to be informed about the deleterious mental health effects of cannabis use in adolescents.

Disclosures:

Dr Wagner is Professor and Chair, Department of Psychiatry and Behavioral Sciences, University of Texas Medical Branch, Galveston, TX. She is President of the American Academy of Child and Adolescent Psychiatry.

References:

1. Gobbi G, Atkin T, Zytynski T, et al. Associations of cannabis use in adolescence and risk of depression, anxiety, and suicidality in young adulthood: a systematic review and meta-analysis. JAMA Psychiatry. 2019;76:426-434.

2. Leadbeater BJ, Ames ME, Linden-Carnichael AN. Age-varying effects of cannabis use frequency and disorder on symptoms of psychosis, depression and anxiety in adolescents and adults. Addiction. 2018;114:278-293.

3. Morin JG, Afzali MH, Bourque J, et al. A population-based analysis of the relationship between substance use and adolescent cognitive development. Am J Psychiatry. 2019;176:98-106.

4. Blair RJ, White SF, Tyler PM, et al. Threat responsiveness as a function of cannabis and alcohol use disorder severity. J Child Adolesc Psychopharmacol. June 2019; Epub ahead of print.

5. Wilson J, Freeman TP, Mackie CJ. Effects of increasing cannabis potency on adolescent health. Lancet Child Adolesc Health. 2019;3:121-128.