Frequent teenage cannabis use: Prevalence across adolescence and associations with young adult psychopathology and functional well-being in an urban cohort

Highlights

• >30% of participants reported past-year cannabis use at age 15, >50% at age 17+.

• Frequent teenage cannabis use (FTCU) between ages 13 and 17 was common (18.2%).

• FTCU was associated with age 20 poorer functional well-being and problematic substance use.

• Frequent teenage nicotine or alcohol use had weaker links with outcomes than FTCU.

• Occasional teenage cannabis use had weaker associations with outcomes compared to FTCU.

Abstract

Background

Amidst cannabis legalization efforts and laws, we do not fully understand how the youngest frequent cannabis users fare during young adulthood. This study aims to 1) examine the prevalence of cannabis use during adolescence, and 2) investigate links of frequent (i.e., weekly or daily) teenage cannabis use with psychopathology and functional well-being at age 20—compared to no or occasional use.

Methods

Data came from a prospective-longitudinal cohort study (assessments from 2004 to 2018, from ages 7–20) in an urban setting (N = 1482). Substance use was assessed with self-reports between ages 13 and 20. At age 20, participants reported on psychopathology (psychotic symptoms, problematic substance use, aggression, and internalizing symptoms) and functional well-being (delinquency, financial difficulties, social exclusion, general well-being, and not being in education, employment, or training). Covariates were based on self-, parent-, teacher-, and behavioral measures.

Findings

Almost one in five adolescents had used cannabis frequently between ages 13 and 17 (26.6% of males, 9.8% of females). Adjusting nearly 20 potential confounders, frequent teenage cannabis use was associated with age 20 problematic substance use and poorer functional well-being compared to the no cannabis use and the occasional use groups. Frequent teenage cannabis use was more consistently associated with age 20 functional outcomes compared to frequent teenage nicotine or alcohol use.

Conclusions

Frequent teenage cannabis use was common and associated with problematic substance use, more delinquency, and poorer functional well-being at age 20. Accordingly, frequent teenage cannabis users could experience increased difficulties in mastering the transitions of young adulthood.

Introduction

Legal and illegal substance use is one of the biggest challenges facing young people in the Western world today. Early substance use in particular is associated with a range of negative outcomes, with high costs for individuals and societies (Degenhardt et al., 2016, Erskine et al., 2015, Vonmoos et al., 2013). In addition to nicotine and alcohol, cannabis is one of the most commonly used drugs (Volkow et al., 2014). Cannabis use during later adolescence and young adulthood, especially frequent use, has been linked with later illicit and problematic drug use (Blanco et al., 2016, Boden et al., 2020, Volkow et al., 2014); certain psychiatric disorders such as psychosis (Arseneault et al., 2002, Bourque et al., 2018, Fergusson et al., 2005b, Volkow et al., 2014); poorer functional outcomes, including delinquency, financial and social problems into midlife (Boden et al., 2020, Cerda et al., 2016, Degenhardt et al., 2013, Fergusson et al., 2002, Green et al., 2017, Horwood et al., 2012, Horwood et al., 2010, Silins et al., 2015, Silins et al., 2014, Taylor et al., 2017), and reduced intellectual ability (Meier et al., 2012) and educational attainment (Horwood et al., 2010, Silins et al., 2015, Silins et al., 2014).

Evidence for associations between adolescent/young adult cannabis use and other psychiatric outcomes (e.g., depression, anxiety) is less consistent (Agrawal et al., 2017, Boden et al., 2020, Borges et al., 2016, Degenhardt et al., 2003, Lev-Ran et al., 2014, Moore et al., 2007, Silins et al., 2014, Smolkina et al., 2017). For example, in a meta-analysis of prospective-longitudinal analyses, zero of three studies found an associations of cannabis use before age 18 with anxiety; three of seven studies, and also the overall meta-analysis, found a significant association with depression (Gobbi et al., 2019). Knowledge about the later well-being of the earliest frequent cannabis users (i.e., younger than 18 years old) is also limited.

Considering the brain’s remarkable malleability during the teenage years—including in response to exposures to psychoactive drugs (Dahl et al., 2018, Fuhrmann et al., 2015, Rubino and Parolaro, 2008, Schneider, 2008, Volkow et al., 2014)—frequent use during these years could be particularly detrimental. A number of cohort studies, including the Dunedin and E-Risk studies (Cerda et al., 2016, Meier et al., 2012, Meier et al., 2018), have assessed problematic and frequent cannabis use from age 18. Others have assessed frequent use at earlier ages (e.g., age 15) but have still missed the earliest teenage years (Boden et al., 2020). Yet others found prevalence rates of early frequent cannabis use to be quite low, making evaluations of links with later outcomes difficult (Copeland et al., 2017). This leaves a gap in knowledge regarding the prevalence and long-term correlates of frequent teenage cannabis use (FTCU), especially in Europe, where rates of teenage substance use tend to be high (Andersson et al., 2009).

Previous cohort studies of later correlates of FTCU have several additional limitations. First, they often do not adjust for other forms of frequent teenage substance use and tend to include limited numbers of covariates. Accordingly, potential confounders of FTCU-outcomes associations are not always adequately taken into account (VanderWeele, 2019). For example, child characteristics such as sensation-seeking and low self-control could explain associations of FTCU with later psychopathology and functioning, but are often not adjusted in previous work. Notably, when several Australasian studies adjusted for large numbers of covariates (e.g., sociodemographics, family functioning, child abuse, childhood characteristics, adolescent behavior), most associations between FTCU and psychopathology and poorer functional well-being in young adulthood remained significant (e.g., Boden et al., 2020; Silins et al., 2014), but these analyses have not been replicated with European samples.

Second, links between FTCU and later externalizing-spectrum outcomes (e.g., aggression, delinquency) are under-examined (e.g., Volkow et al., 2014), perhaps because of cannabis’s reputation as a “peaceful” drug (Sandberg, 2012). Some shorter-term studies have reported that conduct problems predicted subsequent cannabis use, but not vice versa (Defoe et al., 2019). Other, longer-term studies reported associations between chronic (frequent) cannabis use and later arrests/convictions (Boden et al., 2020, Green et al., 2010, Pedersen and Skardhamar, 2010, Schoeler et al., 2016), but were not informative about the types of delinquent behaviors (e.g., minor vs. severe). Associations of FTCU with externalizing behaviors deserve additional attention.

We use a prospective-longitudinal cohort study from urban Switzerland to (1) document the prevalence of cannabis use from ages 13–20, and (2) examine links between FTCU from ages 13–17 with a broad range of age 20 indicators of psychopathology (psychosis, problematic substance use, aggression, and internalizing problems) and poor functional well-being (i.e., delinquency, financial difficulties, perceived social exclusion, poor general well-being, and non-participation in education, employment or training). We are particularly interested in frequent cannabis use, because frequent exposure to THC may have more potent effects on teenagers’ brains and behaviors than rare exposure (Battistella et al., 2014). This could subsequently increase difficulties in mastering the transitions of young adulthood. In addition to direct effects on structural and functional architecture of the brain, frequent early cannabis use could be associated with a preoccupation with drug use over other responsibilities, poor academic attainment (e.g., due to truancy), deviant peer affiliations, involvement in the illicit drug market, and additional outcomes that could impede successful transitioning to young adulthood.

Cannabis use is currently illegal in Switzerland, but possession of small amounts is not punished in some parts of the country; open cannabis use is often tolerated by law enforcement agents (Sznitman, 2009). Where penalties are enforced, they are mild. Legalization debates and trials are underway (Zobel, 2017, Zobel and Maier, 2018, Zobel and Marthaler, 2016), with some proposing 16 as the age of legalization. Accordingly, cannabis use is perceived as relatively safe and normal by Swiss youth (Sznitman, 2009). Large cross-sectional surveys place young people in Switzerland at/above the European average in terms of cannabis use (Andersson et al., 2009). We leverage these high rates of early use to gain deeper insights into how FTCU unfolds, and how it is associated with young adult psychopathology and functional well-being.