Introduction: The Complexity of Cannabis Misuse
Cannabis is one of the most common illegal psychoactive substance used in European
countries, in particular among adolescents and young adults (1). It has been estimated
that almost 55% of adolescents aged 15–19 years have used cannabis at least once in
their lifetime (2), while past year use is reported by approximately 30% of 15–17
year olds and over 47% of those aged 18–19 years (3).
Cannabis use has been associated with several adverse life outcomes including unemployment,
legal problems, dependence, early school leaving, increased risk of developing both
psychotic and affective disorders (3, 4) together with brain structural and functional
abnormalities (5, 6). An association between cannabis use, psychiatric disorders and
suicidal behavior has also frequently been reported, although the exact nature of
this link is still poorly understood (4).
Globally, suicide is one of the most common causes of death among young people aged
10–24 years (6% of deaths), exceeded only by motor vehicle accidents (10%) (7). Over
the last decade suicidal behavior has increased among adolescents and young adults,
there has also been a trend toward the earlier initiation of cannabis use (8). This
has led researchers to investigate the associations between the two factors to determine
if cannabis use may be considered a factor that can trigger suicidal behavior.
Evidence indicates that cannabis use is significantly associated with both attempted
and completed suicides among healthy youths (9) and both twin studies (10) and case-control
comparisons (11) have shown the increased risk of suicide ideation/attempts in those
who use cannabis. Moreover, a longitudinal study found that frequent cannabis use
(at least several times a week) predicted later suicidal ideation in susceptible males
but not females (12). The earlier that this intense use first occurred and the higher
the frequency of cannabis use, faster the susceptible individuals experienced suicidal
thoughts.
Frequent and early cannabis use has also been associated with impaired mental wellbeing
among young individuals (13, 14), and the risk of developing psychiatric conditions
such as psychosis (15) and major affective disorders (16). Specifically, evidence
suggests that cannabis use may exacerbate pre-existing conditions such as bipolar
disorder, and predict negative outcomes and psychosocial impairment (17, 18). According
to longitudinal studies, the high and frequent use of cannabis is also associated
with longer recovery times for affective conditions, more hospitalizations, poorer
compliance with treatment, increased aggression, and poorer response to treatment
in patients with bipolar disorder type I and II (12, 17).
Nevertheless, it is important to note that many of the studies investigating associations
between cannabis use and psychiatric conditions are cross-sectional in nature and
cannot establish a causal relationship between the two phenomena (19). Further, several
studies (20, 21) suggest a bidirectional relationship, as cannabis use variables do
not solely explain the psychiatric outcomes observed nor do pre-existing psychiatric
conditions fully explain the increased use of cannabis. Some researchers (22) have
suggested that individuals with high levels of anxiety sensitivity or hopelessness
may be more sensitive to the negative reinforcement processes of substance use (i.e.,
the ability of substances to modulate negative affective states) than non-affected
individuals; however, some individuals experiencing the onset of mania or depression
are not more likely to report increased cannabis use than those not experiencing these
disorders (23, 24). In addition, other authors (25) have questioned the hypothesis
that individuals may use cannabis to self-medicate psychotic or depressive symptoms.
In summary, cannabis use may be considered only as a risk factor, and possibly one
of a great many that may predict the onset or exacerbation of affective disorders
and suicidal behavior (26). Thus, whether cannabis use can trigger psychiatric disorders
or only precipitate or exacerbate psychiatric conditions in vulnerable individuals,
is still poorly understood.
Affective Symptoms and Hopelessness: A Possible Mediating Factor?
Depression, and in particular hopelessness, are widely recognized as strong predictors
of suicidal behavior (15, 27–29). Specifically, hopelessness has been shown to predict
completed suicides among psychiatric patients after 10–20 years of follow-up (30,
31), and it is significantly associated with both adolescent self-harm and completed
suicides (32).
Studies have also reported that hopelessness may be a risk factor of substance use
suggesting that the presence of hopelessness could be considered a predictor of substance
misuse (33, 34). With regard to cannabis use, Malmberg et al. (22) found that adolescents
with high levels of hopelessness were more likely to have ever smoked cannabis when
compared to adolescents with lower levels. The authors also suggested that increased
levels of hopelessness were usually associated with earlier initiation of cannabis
use. As such, it is possible that young adolescents experiencing hopelessness are
more likely to use cannabis as a strategy to cope with their negative thoughts and
feelings (35).
Informed by such research evidence, we suggest that the presence of hopelessness should
be considered as a specific risk factor of negative outcome and suicidal behavior
among depressed individuals with a history of early cannabis use. Thus in this review,
we propose a theoretical model that addresses this issue (see Figure 1 for more details).
This view is consistent with the hypothesis that early cannabis use may represent
a relevant risk factor that can trigger or exacerbate suicidal behavior in vulnerable
adolescents and young adults, with high hopelessness levels. In addition, vulnerable
individuals may show hopelessness (36) and risk factors such as dysthymic temperamental
traits (37, 38), dysthymia associated with periventricular white matter abnormalities
(39), possibly the S-allele of the serotonin transporter gene polymorphism (5-HTTLPR)
(40), sleep disturbances (e.g., insomnia) (41), abnormal pro-inflammatory cytokines
levels (42), and/or comorbid symptom development (43). We highly recommend that the
complex interaction between these variables is more closely investigated in adolescents
at risk, in order to understand the possible emergence of depression and suicide.
Figure 1
The complex interaction between risk factors involved in the emergence of suicidal
behavior: the mediating effect of hopelessness.
However, studies including those informing the development of this model, should be
considered in the light of significant shortcomings. Many of the studies were conducted
using cross-sectional designs or included retrospective evaluations of lifetime behavior
while attempting to predict long-term outcome variables or making reliable causal
inferences. In addition, these studies adopted different measurements and outcome
variables or they assessed patients at different time points (for more details see
a complete list of limitations within Table 1 in Serafini et al. (15)). Further, not
all studies included specific follow-up periods and only some of them were able to
distinguish between suicide attempts and completions. Furthermore, the use of heterogeneous
samples did not permit some researchers to determine a clear association between the
onset of psychiatric conditions, suicidal behavior and the age of first cannabis use.
Regarding retrospective studies, the absence of any strategies to ensure both inter-rater
reliability and validity of the data also indicates that careful consideration must
be given to the study results. Finally, the patients did not receive psychiatric assessments
using structured psychometric instruments in all studies.
Table 1
Risk factors for suicide risk and early cannabis use in adolescents.
Socio-demographic and social factors
Death/loss of a parent or close friend
Social events including humiliation, loss, defeat, or threat
Interpersonal problems such as romantic difficulties
Poor social support
Financial or employment problems
Availability of weapons
Occasional failure at school or in society
Parental and family factors
Family history of suicide or suicide attempts
Family history of violence and aggression
Parental substance abuse and/or antisocial behavior
Parental separation or divorce
An argument with a parent
Disorganized family environment
History of physical/sexual abuse as a child or childhood maltreatment
Individual factors
Psychiatric disorders such as affective disorders and psychosis
Sleep disturbances such as insomnia
Antisocial and conduct problems
Loneliness
Impulsivity and poor self-control
Hopelessness
Neuroticism
Victimization
History of suicide attempts
Impairments in decisional competence and decision-making skills
Aggressive threats/fantasies
Dysthymic temperamental traits
Sources: van Ours et al. (12), Malmberg et al. (22), Beautrais et al. (49), Bridge
et al. (50), Berger et al. (44), and Reinherz et al. (51).
Implications for Prevention
Psychological distress and social decline need to be carefully investigated in young
adolescents in order to provide appropriate ongoing management (44). Youth suicide
prevention programs aimed at identifying risk behavior and the subgroups of individuals
at high suicidal risk are absolutely necessary in clinical practice. Based on the
current literature, such vulnerable subgroups of individuals include those who used
cannabis early during adolescence (22), those who currently experience hopelessness
(15), and those at high clinical risk of psychiatric conditions (45–47). Furthermore,
vulnerable individuals usually present with additional risk factors that may severely
influence their childhood development [e.g., a poor performance on tasks assessing
sustained attention, impulse control and executive functioning (48)], presumably affecting
both their suicide risk as well as early use of cannabis (12, 22, 44, 49–51) (for
more details see Table 1).
Early warning signs of emerging psychiatric conditions such as behavioral, emotional,
and cognitive changes, should be quickly recognized by clinicians by performing a
multi-dimensional assessment of the patients (52). In addition, we recommend the careful
assessment of hopelessness since it has been demonstrated to significantly increase
the accuracy of suicide risk assessment by allowing the collection of reliable information
about suicide risk even several years after the initial assessment (53). We also suggest
that clinicians assess the current and past use of cannabis in their patients, including
a determination of the age of initial use.
According to the affective model of prevention, young adolescents begin to use cannabis
because they have poor self-esteem, poor self-control, and poor decision-making skills
(35). In this context, youths may also experience negative expectations about their
self and their future related to depression or pervasive feelings of loneliness (54).
Prevention programs aimed at helping young adolescents to clarify their subjective
states, improve their decision-making abilities and enhance their self-esteem are
available, thus potentially preventing the onset of hopelessness and subsequent suicidal
ideation (55, 56). Young adolescents are expected to perceive the information provided
in these programs as credible, otherwise they will not be likely to modify their behaviors
(57). These prevention programs should be conducted during early adolescence and specifically
focused on addressing hopelessness, although it is currently unclear whether the benefits
may vary for different subgroups of adolescents (e.g., younger or older individuals)
(57).
Evidence also suggests that school-based programs are very effective in preventing
and/or reducing the use of cannabis among young adolescents, especially if they are
able to provide active motivational strategies that inform adolescents about the prejudices
against using psychoactive medications (55–57). For example, typical strategies may
include actively explaining how to implement non-use behavior, such as coping skills
for prodrug pressures and negative affective states, helping youths to understand
that most people do not use cannabis, as well as increasing their awareness of the
consequences of cannabis use and benefits related to non-use (57). In particular,
research has demonstrated the efficacy of social-influence programs that use interactive
(not didactic) sessions, and those that encourage active participation in small groups
(55, 56).
In summary, clinicians need to be aware of the importance of preventive programs that
are directed at preventing/treating modifiable factors such as adolescent hopelessness
and/or delaying early cannabis use in specific subgroups of adolescents who experience
major affective disorders.
Conclusion
Suicide, cannabis use, and psychiatric conditions (e.g., depression) are likely to
be underpinned by similar complex factors. Of particular interest for clinicians is
the identification of individuals at risk of suicide who show early (i.e., prodromal)
affective symptoms such as hopelessness. Suicide prevention programs may provide additional
benefits if they focus on delaying or reducing adolescent cannabis use as well as
responding to early signs of depression and hopelessness, which are widely recognized
as important risk factors for suicide (58).