The elevated risk of suicide among youth exposed to bullying (or peer) victimization is a significant concern (see van Geel et al.,
2021, for a meta-analysis), the more so because both bullying victimization (Modecki et al.,
2014) and suicidality (incorporating a range of suicidal ideation and behaviors; Cha et al.,
2018) are prevalent among young people. A better understanding of the mechanisms that link bullying victimization to suicidality in young people is needed to inform health policies, preventive screening, and interventions (Hong et al.,
2015). Thus, the current study aimed to investigate potential mediators of this link, focusing on internalizing problems (i.e., depressive and anxiety symptoms) and substance use (i.e., tobacco, alcohol, and cannabis use). This study focuses on suicidal ideation as the outcome, owing to its strong links to suicidal attempts and completion (e.g., Castellví et al.,
2017). To provide a developmental perspective and to help disentangle the processes occurring within young people over time from between-person confounds, this study used the random-intercept cross-lagged panel model (RI-CLPM) in a high-quality longitudinal dataset spanning ages 15 to 20.
Bullying is commonly defined as repeated intentional aggressive behavior that involves a power imbalance between perpetrators and victims (Olweus,
1993). There is ample evidence suggesting that bullying victimization is associated with subsequent suicidal ideation among youth (see van Geel et al.,
2021, for a meta-analysis). However, exposure to bullying victimization may act via triggering certain psychological or behavioral processes that can lead to suicidality, and those processes are not well understood or rigorously examined (Hong et al.,
2015).
According to the general strain theory (e.g., Agnew,
2001), for instance, internalization or substance use may function as (maladaptive) coping mechanisms evoked by strains (e.g., bullying victimization). In this view, suicide is conceptualized as a kind of self-directed, escapist coping response (e.g., Walls et al.,
2007), which may be a last resort, especially in the absence of effective coping resources to buffer the influence of repeated exposure to uncontrollable interpersonal stressful life events. Moreover, from the three-step theory (3ST, and psychache theory) perspective (Klonsky & May,
2015), suicidal ideation can begin with psychological or emotional pain (e.g., internalizing problems), and bullying victimization/social rejection may be a significant source of eliciting distressing feelings in youth. Combining these two theoretical perspectives (i.e., the general strain and three-step theory), internalizing problems may act as mediators linking victimization experiences and suicidal ideation.
In addition to the aforementioned general strain theory, the effects of substance use on suicidality have been extensively investigated, and the potential mediating role of substance use in the victimization-suicidality link has been tentatively indicated by empirical studies. Possible explanations for the role of substance use as a mediator in the victimization-suicidality link, for example, include the idea that substance use, as one possible coping mechanism for victimization experiences, may impair judgment, worsen impulse control, or increase the risk of neurocognitive dysfunctions, resulting in suicide risk (e.g., Pompili et al.,
2012). A related idea is that substance use may be co-occurring with psychopathology (e.g., depressive symptoms, Hunt et al.,
2020), which may in turn increase suicide risk. However, a lack of theories incorporates problematic substance use into the association between interpersonal stress and suicidality. Given indications from empirical evidence suggestive of its role, it will be critical to further evaluate it as a mediator to inform the enrichment of suicide theories.
Some empirical studies have investigated mediating effects of depressive and anxiety symptoms, and substance use on the relation between victimization and suicidal ideation. However, the majority of these studies employed a cross-sectional design, making it difficult to discern temporal order. Indeed, previous authors have highlighted that cross-sectional mediation analyses can produce misleading findings (Maxwell & Cole,
2007). For example, a cross-sectional study surveyed 403 (ages 13–16 years) American adolescents and found that traditional/cyber victimization was indirectly related to suicidal ideation through depressive symptoms (Fredrick & Demaray,
2018). Another cross-sectional study, recruiting 12,354 Chinese adolescents (ages 10–21 years), indicated that the effects of bullying victimization, witnessing, and perpetration on suicidal ideation were linked via depressive symptoms and negative coping styles (Duan et al.,
2020). Regarding anxiety symptoms, a study based on 488 American adolescents (ages 10–18 years) found no evidence that the indirect effect of anxiety symptoms on the cross-sectional relation between bullying victimization and suicidal ideation when family conflict, depressive symptoms, and substance use were also included in the model (Lardier et al.,
2016). However, a longitudinal study showed that bullying victimization predicted self-harm thoughts via emotional problems (reflective of anxiety symptoms) and depressive symptoms in a small group of adolescents (
n = 112;
Mage = 14.14,
SD = 1.81) from high-risk communities (i.e., respondents with discipline issues) who participated in two interviews at a 6-month interval (Bryson et al.,
2020).
Concerning the empirical evidence that on the mediating role of substance use, one cross-sectional study suggested that physical/cyber bullying victimization was associated with substance use (including seven forms of substance use, e.g., alcohol, tobacco) and violent behavior, which was in turn related to suicidality among American adolescents (
n = 4693, ages 14–19 years; Litwiller & Brausch,
2013). A similar cross-sectional study has also been carried out with American youth (
n = 15,364, ages 12–18 years; Moon et al.,
2015), supporting the indirect effect of substance use (including legal and illegal substance use, e.g., smoking marijuana) on the victimization-suicidality association. A study of 238 Canadian adolescents investigated the longitudinal relations between peer victimization, alcohol use, and suicidal ideation, using a cross-lagged panel model (CLPM) (Marschall-Lévesque et al.,
2017). The results suggested that age 13 victimization was associated with age 14 suicidal ideation, which in turn predicted age 15 alcohol use; however, a direct test of mediation was not performed.
Bidirectional Associations between Bullying Victimization, Substance Use, Internalizing Problems, and Suicidality
A further issue that needs to be addressed is that research evaluating these mediating mechanisms has been mostly limited to the unidirectional pathway from bullying victimization to suicidal ideation, which may oversimplify the complex processes underlying these links (e.g., Zhu et al.,
2021). For example, youth suffering from suicidality (e.g., Speckens & Hawton,
2005), depressive symptoms (e.g., Rudolph et al.,
2008), anxiety symptoms (e.g., de Lijster et al.,
2018), and/or substance use (e.g., Unger et al.,
2003) are more likely to display significant social-behavioral deficits such as using less effective, mood-based, or conflict solutions on social problem solving, or engaging more impulsive (e.g., Verdejo-García et al.,
2008) and aggressive behaviors (e.g., Doran et al.
2012). As a result, these youth may create negative social circumstances in which they exhibit a distinctive pattern of social behavior that may elicit disliking or aggressive responses from their peers and/or may result in them being perceived as an easy or desirable target, making them more vulnerable to victimization. These speculations on how suicidal ideation, internalizing problems, and substance use can also lead to increases in the risk of bullying victimization are supported by some empirical evidence where they have been examined (see Christina et al.
2021, for a meta-analysis); however, there also remains a need to examine these links using statistical methods that can disaggregate between- and within-person associations.
Differential Effects of Substance Use Types
Previous evidence has suggested relations between substance use and suicidal ideation might be complex and are not yet fully understood. Specifically, there might be variation in the magnitude and consistency of the associations between different types of substance use with suicide ideation, among which alcohol, tobacco, and cannabis use have received extensive attention. For example, a meta-analysis study indicated positive longitudinal associations between cannabis use in adolescence and suicidal ideation in young adulthood (Gobbi et al.
2019), which is consistent with previous review work (e.g., Schmidt et al.
2020). However, a recent meta-analysis of prospective cohort studies covering a wide range of age groups suggested a significant prospective effect of alcohol use on suicidal attempts and completed suicide but not on suicidal ideation (Amiri and Behnezhad
2020), which was corroborated by another meta-analysis indicating no significant effect of alcohol reduction on suicidal ideation (Witt et al.
2021). This could be because despite the fact that other evidence has shown suicidal ideation to strongly predict suicidal attempts, alcohol use may play a particularly important role in impulsive or unplanned suicidal behavior (e.g., suicide attempt with no prior suicidal ideation) (e.g., Schilling et al.
2009). A few longitudinal studies have focused on the relation between tobacco use and suicidal ideation in young people but yielded mixed findings: Some supported the positive link between the two (e.g., Bronisch et al.
2008) while others did not (e.g., Boden et al.
2008). Although more research is needed, a small number of studies suggested the reverse pathway from suicidal ideation to substance use in young people (e.g., Marschall-Lévesque et al.
2017), which supports the self-medication hypothesis (i.e., substances might be used to cope with or self-medicate suicidal thoughts). Taken together, there is a clear need for further research to clarify the direction of longitudinal relations between suicidal ideation and the use of different substances among young people.
Increased Suicide Risk in the Transition from Middle Adolescence to Adulthood
The developmental stages from middle adolescence to emerging adulthood (i.e., from ages 15 to 20) were the particular focus of this study, as the suicide rate is higher in older adolescents than in younger adolescents (Glenn et al.
2020). The lifetime prevalence rate of suicidal ideation has been found to be in the range of 19.8–24.0% and 19.5–25.3% for adolescence (see Nock et al.
2008, for a review) and young adulthood (see Mortier et al.
2018, for a review), respectively. Further, the suicide-related risk factors examined in this study, e.g., internalizing problems and substance use, increase as young people age across adolescence and into young adulthood. For example, it is estimated that globally, 34% of youth aged 10–19 years are at risk of developing depressive symptoms (Shorey and Wong
2021), with youth aged 15–19 showing a higher rate of depressive disorder compared to those aged 10–14 (World Health Organization
2021). Concerning substance use, globally, 13.6% of youth aged 15–19 years have engaged in heavy episodic drinking in 2016, and about 4.7% of adolescents aged 15–16 years used cannabis at least once in 2018 (World Health Organization
2021). These have a major individual and societal cost, with mental health issues (World Health Organization
2021) and substance use (Degenhardt et al.
2016) each accounting for more than 10% of the worldwide burden of disease and injury among youth. Though not as common as in early adolescence, bullying victimization remains common at this age), with an average prevalence of 35% for traditional victimization and 15% for cyber victimization among youth aged 12–18 (Modecki et al.
2014). Taken together, the transition from middle adolescence into adulthood may represent a critical period to capture how earlier victimization experiences cascade into later suicide risk.