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Original Articles

A Systematic Review: Adolescent Cannabis Use and Suicide

Schmidt, Kristen MD*; Tseng, Irene BS; Phan, Amanda BS; Fong, Timothy MD; Tsuang, John MD

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Addictive Disorders & Their Treatment: September 2020 - Volume 19 - Issue 3 - p 146-151
doi: 10.1097/ADT.0000000000000196
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Abstract

Cannabis is the most frequently used illicit drug and it has been reported as the most common illicit substance detected on toxicology screens of persons who completed suicide.1,2 As cannabis access, availability and policies evolve, it becomes more critical to identify subpopulations of cannabis users who are most at risk for suicide. One such population that may be especially at risk is adolescents.

Adolescents continue to have the highest suicide rates of any segment of the population.3 The incidence of suicide in this group is estimated at 16.8% of all deaths in the age group 10 to 24.4 Death rates due to suicide in adolescence are eclipsed only by motor vehicle accident fatalities. A consistent theory behind the elevation of suicide in this group is the impulsivity associated with prolonged myelination processes. Many argue that the process of neuromaturation and brain development is not complete until age 25, with the final stages of synaptic pruning, at which time impulsivity might be reduced. This lack of maturation, with poor impulse control, might lead to increases in suicide among adolescents.5

A lack of prefrontal inhibitory control is also posited as the rationale for substance use experimentation in this cohort.5 Increasing access to cannabis due to recent legalization measures may have negative consequences for this subpopulation. To our knowledge, this is one of the first comprehensive reviews of its kind evaluating the association between cannabis use and suicide risk among teenagers since the implementation of new cannabis laws. With much of cannabis law still to be determined, an examination of the evidence is necessary to help guide public policy. Such a review may be a crucial step in determining an appropriate legal age for purchasing cannabis.

We performed a comprehensive review of the literature from the past 29 years examining the association between suicide risk and cannabis use in adolescents. General epidemiological studies and analyses of co-occurring mental health disorders were also included to discern the relationship between suicide risk and cannabis use, with studies focusing on adolescents highlighted in the current review.

MATERIALS AND METHODS

A comprehensive PubMed and Google Scholar search was conducted to ultimately yield 12 papers: a single review, 3 longitudinal studies, 7 cross-sectional investigations, and 1 letter to the editor. We referred to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart and the checklist in the process of selecting our studies. On PubMed, we searched for key words “marijuana OR cannabis OR THC OR tetrahydrocannabinol, suicide, and adolescents” from January 1, 1990, to December 1, 2019. This yielded 344 studies. Only human studies were analyzed, and we further narrowed our search to the subpopulation of adolescents in the PubMed search engine. The PubMed search engine defines adolescents from the ages of 13 to 18 years old. Studies that were outside the scope of our focus on these 3 subjects (cannabis, suicide, and adolescents) were excluded. We excluded papers that were not in English. We used the Google Scholar search engine to supplement our selection of papers. After removing for duplicate papers between the 2 search engines, and screening to ensure that all literature we selected were available in the full-text format, we were left with 12 papers.

We recognize that our search criteria is subject to publication bias and dissemination bias, as we only included published studies that we could access at the time of our search. We also recognize that our review may be subject to selective reporting within studies biases, as we only reported findings of the studies that were pertinent to our focus on adolescent cannabis use and suicidality. Last, we acknowledge that our paper might be subject to interpretation bias, as our analysis of the findings of each paper we collected could influence the results of this review.

RESULTS

After a comprehensive PubMed and Google Scholar search was conducted, we found 12 papers that evaluated the relationship between cannabis use, suicidal behavior, and adolescence. There was a single review, 3 longitudinal studies, 7 cross-sectional investigations, and 1 letter to the editor. Only 1 study failed to show an association between suicidal risk, adolescence and cannabis, while all other studies showed significant associations. We have summarized all the relevant studies below.

In 2000, Hilman et al6 published a targeted literature review on suicide and drug use in an effort to determine prevention strategies for Western Australian (WA) youth. The methodology was 2-fold: (1) National and international literature was reviewed; and (2) clinical, toxicology, and psychological reports for 571 youths who completed suicide in WA were examined. Results suggested that illicit drugs were detected in nearly a third of WA male and >25% of female suicide completers. The most common substances detected in suicide completers were alcohol and cannabis. Against the background of a literature review, the authors concluded that a sizable number of suicide attempts (SAs) may be independently accounted for by cannabis use given its high prevalence in WA. Limitations of the review include studies with varying substances, differing measures of suicidality, and a low number of longitudinal studies available.6

Three studies looked at suicide risk and behavioral correlates in adolescents using a prospective methodology. Roberts recruited 4175 persons ages 11 to 17 by telephone in the Houston metropolitan area and queried them by survey and diagnostic interview about SAs and risk factors.7 Follow-up utilizing the same screening measures was performed a year later and 75% (3134) of the sample remained.8 Cannabis use was one of only 2 independent predictors of the first incidence for SA with an odds ratio (OR) of 4.7. The study also found that a substantial proportion of subjects reporting attempts had no plan before the attempt (59% of first responders and 43% of follow-up responders). This suggests that impulsivity may be a significant component of SA in adolescents and may be worsened by cannabis or other substance use. Limitations of this study include self-report assessment, lack of collateral from parents and some loss to follow-up.8

In a further effort to identify risk and protective factors for adolescent SAs, Borowsky investigated what role race and sex might play. Data from the national longitudinal study of adolescent health (ADD health) was analyzed. This included 134 schools and employed students attending grades 7 to 12. There was an in-school survey as well as an interview conducted at subjects’ homes. Follow-up was obtained 11 months later. Results suggested that there was a relationship between cannabis use and SA with OR of 10.3 for black females; 4.5 for Hispanic females; 3.4 for white females; 5.9 for black males; 2.9 for Hispanic males; and 6.8 for white males as compared with nonusers. Age, family structure and welfare status was controlled for in capturing these results. Of note, the study also found that the presence of at least 3 protective factors [such as parental-family connectedness, positive emotional well-being, high Grade Point Average (GPA), school connectedness] reduced the risk of SA by 70% to 85%. Limitations include a small number of youth in sex and ethnic subcategories, self-report bias, and potential of parental influence for home interviews.9

Fergusson and colleagues also found a significant dose-response relationship between cannabis use in adolescence and later SA in a prospective analysis of a New Zealand birth cohort. The methodology of the study included a cohort of 1265 children as part of the Christchurch Health and Development Study comprised of parental interviews, teacher reports, self-reports, and other data. The sample included 1063 subjects and controlled for confounding variables including adverse life events, peer affiliations, age of leaving school, age of leaving home, and alcohol abuse/dependence. They found that 14- to 15-year-olds who were weekly cannabis users had an OR of 13.1 for SAs and an OR of 7.3 for suicidal ideations (SIs), compared with nonusers. These ratios declined at ages 20 to 21 to 1.8 for SI and 0.8 for the SA. Associations between cannabis use and increased rates of crime, depression, other drug use, SI, and SA remained significant after adjusting for confounding. Limitations included a loss to follow-up, selection bias, and self-report.10

The other investigations evaluating suicidal behavior and cannabis use in adolescents were cross-sectional. Maharajh and Konings did a cross-sectional study in Trinidad, which has the second-highest suicide rate internationally and cannabis use is reported by 16% of adolescents. The study attempted to elucidate the relationship between depressive and psychotic symptoms, suicide, and cannabis use. A self-report survey was completed by 227 students ages 12 to 20 querying for psychotic and depressive experiences. The authors suggested that there is a relationship between cannabis use, depression, and suicidal behavior. Limitations of the article include the fact that the study data was not well described; there was no mention of how cannabis use was assessed or suicidality determined (ideation, attempts, completions), and no mention of exclusion/inclusion criterion. In addition, as is the case with all cross-sectional studies, causality cannot be determined.11

In a later study, Chabrol and colleagues found that cannabis use did appear to independently predict suicidal behaviors after controlling for psychiatric symptoms such as depression and anxiety in adolescents. They queried 248 high school students ages 15 to 20 using an anonymous survey that asked about cannabis use, psychiatric symptoms, SI and SA. Results demonstrated that cannabis use was significantly associated with higher rates of SI and SA, anxious and depressive symptoms, and that the association with cannabis use remained independent of psychiatric symptoms. Limitations included the cross-sectional nature, lack of assessment of cannabis use frequency, and lack of control for other variables including other drug use.12

Cho and colleagues was interested in the question of drug use onset and suicide risk in adolescents. Researchers had 1252 adolescents in grades 9 to 11 complete surveys about substance use and suicide. The onset of cannabis use was not associated with any suicide risk factor for girls or boys; however, boys currently using cannabis did have a higher endorsement of suicide as “an option” compared with those not using cannabis. This study highlighted sex differences in substance use and associated suicide risk. Limitations included the fact that the study was less generalizable due to the fact that >60% of the subjects were below median GPA and upper quartile truancy and receiving education in an urban setting. The study was also cross-sectional and retrospective bias applied to surveys.13

Another cross-sectional investigation aimed at clarifying the relationship between drug use patterns and adolescent suicidality. This comprehensive study surveyed 73,183 high school students between the years 2001 and 2009 as a part of the Youth Risk Behavior Study. Ten substances were included: alcohol, tobacco, cannabis, cocaine, ecstasy, heroin, hallucinogens, inhalants, methamphetamine, and steroids. In addition, multiple variables were controlled to exclude confounding such as demographics, violence, sexual behavior, eating disorders, and symptoms of depression. After controlling for these variables, cannabis was shown to have a significant relationship with suicidal risk. Cannabis prevalence in the sample was 39.1% and predicted SI with an OR of 1.4 (1.3-1.5); suicidal plans with an OR of 1.3 (1.2-1.4); SA with an OR of 1.6 (1.4-1.8); serious SA needing medical attention with an OR of 1.8 (1.5-2.3). Increased risk of suicide was found to be most significantly associated with heroin use and a higher lifetime total substance use. Limitations included the lack of controlling for psychiatric comorbidity and the cross-sectional, self-report nature of the study.14

In another cross-sectional study utilizing the Youth Risk Behavior Survey, researchers found that the use of crack cocaine, rather than heroin, was most strongly associated with SA in North Carolina public school students. That same study did find that the use of cannabis was also associated with SA as well as serious consideration of suicide or making suicidal plans. Felts and colleagues provided the survey to ninth and 12th graders. However, exclusion of confounding variables was not performed and there was no analysis comparing responses between ninth-grade and 12th-grade students. Further limitations include the cross-sectional nature of the study and self-report bias.15

King and colleagues published the only negative study in the series of investigations evaluating cannabis use as a risk factor for suicidality in adolescents. This study employed 1285 youths ages 9 to 17 and queried students as well as care-takers for collateral. Subjects were a part of the National Institute of Mental Health Methods for the Epidemiology of Child and Adolescent Mental Disorders Study. They looked at the association between psychosocial and risk behaviors in adolescent SAs and SI. The study found that 42 had attempted suicide, while 67 had SI; and 109 had either SI or SA. While they found that SI and SA were significantly associated with a history of cannabis use after controlling for demographic factors, cannabis use was no longer significant when psychiatric disorders were controlled for as a confounder. Limitations include the fact that frequency and amount of cannabis was not captured and combining the groups of SI and SA in the analysis may have skewed results as these can be very disparate populations. The study was cross-sectional and based on self-report.16

A recent cross-sectional study international study conducted by Carvalho and colleagues looked at 86,254 adolescents in 21 different countries. The study focused on 12- to 15-year-olds and assessed the relationship between cannabis use and SAs. These authors included control variables of sex, food insecurity, age, alcohol consumption, smoking, amphetamine use, and anxiety-induced insomnia. The anxiety-induced insomnia was a control variable intended to serve as a proxy for other mental illness, such as depression. Statistical analyses showed that cannabis use within the last 30 days or any use during lifetime was associated with greater SAs. Overall, the prevalence of SAs was 10.1% among these adolescents, and after adjusting for all potential confounders, there was a 2.30 [95% confidence interval (CI)=1.73-3.04] times higher odds of SA in those who had used cannabis in their lifetime. In adolescents who had used cannabis within the last 30 days, there was a 2.03 increased odds of SA (95% CI=1.42-2.91). However, the authors to note that due to the cross-sectional nature of this study, it is difficult to ascertain whether the relationship between cannabis use and the SA is causative. Self-reporting bias may also be present in this study. In addition, the control variable of anxiety-induced insomnia may not necessarily serve as a complete proxy for depression or other mental illness, thus resulting in a large confounder that may have been overlooked.17

In a letter to the editor, Clarke and colleagues described a small prospective study concerned with evaluating the impact of adolescent cannabis use, mood disorders and lack of education on later SAs in young adulthood. The study included 140 students who had screened positive for significant SI matched against 174 controls. Students then received a structured clinical interview with their guardian and follow-up was obtained 8 years later with 79% of subjects. Results demonstrated that adolescent cannabis use was an independent risk factor for SA with an OR of 7.5 (95% CI=1.2-43.8). The study was limited by the potential of parental influence during the interview, not accounting for a history of previous SAs, and loss to follow-up.18

DISCUSSION

A review of the literature of the past 29 years suggests that adolescence appears to be the population of cannabis users most at risk for suicidal behavior as demonstrated by multiple prospective studies. Roberts and colleagues highlighted that cannabis use was an independent predictor of first incidence for SA in adolescence (OR=4.7); while Borowksy and colleagues’ national longitudinal study identified black and Hispanic females as being particularly associated with increased SAs in grades 7 to 12 (OR of 10.3 and 4.5, respectively).7–9 Frequency of use in adolescence was a significant risk factor with 13 times the amount of SAs in 14- to 15-year-olds using cannabis weekly compared with cannabis naive teens.10 A large scale cross-sectional study conducted by Carvalho et al17 demonstrated that adolescents with cannabis use within the last 30 days, and adolescents with any lifetime cannabis use had higher likelihoods of attempting suicide. As cannabis laws change, clinicians need to become aware of patients, such as adolescents, who are at especially high risk to incur detrimental outcomes with the use of cannabis. Greater efforts should be undertaken by physicians to screen such patients for suicide and provide informed consent about cannabis risk. Much more needs to be examined about the relationship between cannabis use and the initiation, maintenance or reactivation of suicidal thoughts, feelings, or behaviors.

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Keywords:

adolescent; cannabis; marijuana; suicide

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