Tell me who your friends are?! The mediating role of friends’ use in cannabis abuse

Abstract Objectives To evaluate the relationship between age at onset of cannabis use and cannabis abuse in a sample of Portuguese cannabis users, testing the mediating role of the number of friends using cannabis and comparing these relationships between male and female subsets. Method A sample of 529 Portuguese cannabis users comprising 276 males and 244 females aged from 14 to 21 years completed a sociodemographic questionnaire, the Cannabis Abuse Screening Test (CAST), and answered four questions related to cannabis use. Data were analyzed using the PROCESS macro in SPSS version 26.0. Results Age at onset of cannabis use was negatively related to the number of friends using cannabis, while the number of friends using cannabis had a positive relationship with cannabis abuse. As predicted, the number of friends using cannabis seems to have a mediating role in the relationship between cannabis onset age use and cannabis abuse, since the indirect effect was found to be significant. The pattern of the relationships among the variables observed was found to be similar for both male and female subsets of the sample. However, males reported higher cannabis abuse than females. Conclusion The results highlight the mediating role of friends’ use of cannabis in the relationship between age at onset of cannabis use and users’ abuse. These results highlight the importance of early intervention in cannabis use. In particular, the pattern of the relationships observed among the studied variables emphasizes the need to monitor and conduct peer training interventions or interventions to promote of social skills.


Introduction
According to the World Health Organization (WHO), 1 cannabis is a psychoactive substance of natural origin that exerts an action on the central nervous system and modifies one or more of its functions, perceptions, emotions, attitudes, and behaviours. 1 It is currently the most widely used illicit substance 2 and it has been estimated that 3.8% of the global population between 15 to 64 years old used cannabis in the past year, an increase of about 30% between 1998 and 2017.
Among Europeans aged from 15 to 34, estimated use is around 15%, rising to 19.2% among those aged 15 to 24. 3 In Portugal, prevalence of cannabis use has been estimated at 9.7% between the ages of 15 and 74, with 4.5% reporting use in the previous 12 months. 4 According to a survey of young people participating in the National Defense Day, aged 18 in 2019, prevalence of cannabis use in the last year reached 26.9%. These data allow us to understand the extent of this public health problem. In fact, cannabis is the most used illicit substance, regardless of age, gender, or region of residence, with a prevalence of consumption during the last year that is higher than the European average and still increasing. 4 Some factors have been associated with cannabis use. It tends to be higher in males, [5][6][7][8] related to parenting practices and parental cannabis use, [9][10][11][12] as well as to friends' use. [13][14][15] Also, ease of access, 8 in a culture of complacency or permissiveness, 16 being perceived as harmless 17,18 and even normalized, 19 contribute to its growing use among adolescents.
In a developmental period that is well-known for its challenges and changes, 20 during which the peer group becomes a source of identity and bonding, students desire to "fit in" and substances are used as a strategy to manage their anxiety, particularly regarding schoolwork, sense of academic failure, and lack of social support. 21 Although some studies have already explored the effect of friends on cannabis use [13][14][15] or age at onset of cannabis use on other psychopathological problems 22,23 and cannabis abuse or other harmful substance use behaviours, 7,24 there is a lack of evidence relating to the mediating role of friends' use in the relationship between age at onset of cannabis use and users' abuse of this substance.
The present study explored the relationships between age at onset of cannabis use, number of friends using cannabis, and cannabis abuse, in particular, testing the mediating role of the number of friends using cannabis. In addition, since previous studies suggest a moderating role of certain demographic characteristics, 5-8 such as when comparing men and women, 5 the current study explored the relationships among the age at onset of cannabis use, the number of friends using cannabis, and cannabis abuse, comparing male and female subsets. Bearing in mind the conceptual model under study, this paper has the potential to contribute to both literature and practice.
First, we explore the mediating role of the number of friends using cannabis, contributing to explain the relationship between the age at onset of cannabis use and cannabis abuse. To the best of our knowledge, this is the first study testing a more complex model by including the number of friends using cannabis as an intervenient variable that contributes to explain the relationship between the age at onset of cannabis use and cannabis abuse. Second, the current study tests whether there are differences between males and females in the relationships between age at onset of cannabis use, number of friends using cannabis, and cannabis abuse. Furthermore, based on the results obtained, we expect to contribute to indicating a set of practices to be implemented in the psychotherapeutic process with cannabis users and peer training or promotion of social skills interventions focused on social groups with a history of substance use.

Age at onset of cannabis use and cannabis abuse
Several studies in the literature report increasing cannabis use, particularly since the end of the first decade of the millennium, 6,25 with the largest percentage of first experimentation with cannabis occurring before the age of 20. 26 According to a systematic review of studies on the prevalence and risks of cannabis use disorder among users, performed by Leung et al.,27 one in every eight individuals who use cannabis will develop cannabis dependence, with the greatest risks associated with early initiation and frequent use in the adolescent population. Similar evidence is found in the literature. Adolescents who started using cannabis before 15 years of age were at higher risk of developing drug abuse symptoms by age 28. 24 This issue assumes particular importance since several studies associate higher risks of cannabis and other drug abuse with early age of onset. 7,26-28 A proportion of subsequent adverse educational outcomes, [28][29][30] and early, frequent, and heavy cannabis use, is strongly associated with cognitive and mental health problems in adulthood. 31 Moreover, evidence shows that brain impairment is greater in adolescents who use cannabis when compared with adults. [32][33][34] Bearing in mind the literature, this study's first hypothesis was as follows: Hypothesis 1 (H1): age at onset of cannabis use has a negative relationship with cannabis abuse.
Indirect effects: a proposal for the mediating role of the number of friends using cannabis As previously noted, the literature suggests that age at onset of cannabis use is significantly related to cannabis abuse. 27 Going one step further, the current study suggests that beyond this direct relationship, an indirect relationship can also occur via the number of friends using cannabis.
In the literature, most studies explore the relationship between the number of friends using cannabis and cannabis abuse. Some authors point out the role of socialization and identification with groups that they consider to be similar from the point of view of substance use. 35 Also, through social learning, 36 adolescents imitate their high-status peers, leading to involvement in cannabis use. 37 Particularly with the increasing time children and adolescents spend at schools, this context assumes a determinant role in their behaviors. Authors such as Fletcher et al. 21 explore how this context influences drug use and find three main motives: students who do not identify with indicators of success find a source of identity and connection in substance use; students who want to feel included in schools that are considered unsafe and the use of drugs facilitating this process; but also substance use might be used as a coping strategy for schoolwork or unhappiness. 21 Regardless of the motives, several studies have identified friends using cannabis as a predictor of substance use. 15

Comparing males and females regarding the relationships studied
In the literature, we find consistent data related to higher rates of cannabis use in males than females. [5][6][7][8] This trend is similar for overall substance use and, according to the European Drug Report 2021, cannabis was used by approximately 47.5 million males compared to 30.9 million females in the European Region. 3 This trend is naturally followed in Portugal, not only in overall cannabis use, but also in moderate to highrisk use in men and women. 4 Authors of a longitudinal study with male-female sibling pairs spanning more than 20 years explored factors related to substance use disorders. 45 If males were at higher risk of earlyonset alcohol use, the trend for cannabis was the opposite. Females tend to be involved in cannabis use earlier than males. Along the same lines, authors find gender differences in the developmental trajectories of substance use progression between substances. 46 Not only does the effect of cannabis use onset age seem to be different between men and women, 47,48 but these differences have also been explored considering the roles of group membership, identity construction, and relations with peers in terms of their influence on cannabis use patterns. 49 Bearing in mind the findings of these abovementioned previous studies, it is possible to expect males and females to differ in terms of the relationships analyzed in the present study. As such, this study's third hypothesis was as follows: Hypothesis 3 (H3): the relationships between age at onset of cannabis use, the number of friends using cannabis, and cannabis abuse differ comparing the male and female subsets.

Method Procedures and sample
The sampling procedure used was a nonprobabilistic sample with a convenience sampling approach. The questionnaire was administered in  Table 1.

Descriptive statistics
On average, the participants of the present study

Hypothesis testing
The correlation results provide a general idea of the pattern of the relationships between the constructs.
Thus, the next step in data analysis, before mediation testing, consisted of estimating a model that included only the direct relationship between cannabis use onset age and cannabis abuse (Figure 1). This model was tested without the hypothesized mediating variable (i.e., number of friends using cannabis) and a negative relationship was observed for the total sample, and for Proceeding with the hypotheses testing, another model was tested with the hypothesized mediating variable (i.e., number of friends using cannabis) included. As can be seen in Figure 2, negative relationships were found between age at onset of cannabis use and the number of friends using cannabis for the total sample and for the male and female subsets analyzed separately (β = -0.20; p < 0.01; β = -0.23; p < 0.01; β = -0.17; p < 0.01; respectively).
In turn, positive relationships were found between the number of friends using cannabis and cannabis abuse for the total sample and for the male and female subsets analyzed separately (β = 0.28; p < 0.01; β = 0.29; p < 0.01; β = 0.35; p < 0.01; respectively).
Bearing in mind the results presented in Figure 1 for the direct relationship between age at onset of cannabis use and cannabis abuse, it can be observed that this relationship was weakened when the mediator variable was included in the model ( Figure 2 and females did not differ significantly in terms of the relationship between the age at onset of cannabis use and the number of friends using cannabis (z = 0.62, not significant), the relationship between the number of friends using cannabis and cannabis abuse (z = -0.08, not significant), or the relationship between age at onset of cannabis use and cannabis abuse (z = 1.47, not significant). Therefore, H3 was not supported.

Discussion
The main purpose of the present research was to study an unexplored mediating role of the number of friends using cannabis to explain the relationship Cannabis abuse

Conclusion
The present study allows us to confirm the mediating role of the number of friends using cannabis in the relationship between the age at onset of cannabis use and users' abuse. The mediation effect found is a very interesting finding, since it allows us to theorize and understand the effect of the variables, with implications for prevention and intervention programs.
In a context of increasing complacency or permissiveness, these findings allow us to understand the crucial role of early intervention, in educational contexts, preventing early exposure of youth to cannabis risk, but also the need to monitor and conduct peer training interventions or promotion of social skills focused on social groups with substance use history. Selective programs might be important in this strategy to delay onset age, decrease the level of cannabis abuse, or motivate treatment. Given the trend of increasing prevalence of cannabis use in European countries and the age of onset, efforts should be strengthened not only to avoid the escalating effect that is to be expected, but also to postpone or prevent experimentation by new users. Besides face-to-face interventions, new strategies using new technologies should also be implemented to address this public health problem.