Country-level rates of drunkenness (from 10% to 37%) and cannabis use (from 4% to 35%) varied widely across school students in Europe. Perceived use of friends (i.e., descriptive norms) was found to be the most important factor that was associated with personal risky alcohol and cannabis use in our sample. Several studies on substance use in European university or college students arrived at comparable results, showing that perceived peer substance use exerts high behavioral influence on emerging adults [28,29,30]. However, less research has been conducted on secondary school students in Europe. A study from Switzerland [10] was in line with our European results, finding that perceived drunkenness and cannabis use were associated with the corresponding personal use among eighth and ninth graders. Additionally, the authors report that a stronger relation between personal use and perceived peer use was found in classes where school students came cannabis-intoxicated to school or used cannabis in school premises than in schools without such incidences [10]. Such associations between the perceptions of peer use and personal use were also identified in European [31] and US adolescents [32]. The cannabis use of friends seemed to be more important among adolescents than the use of adults or siblings [33].

The fact that school students are vulnerable to their friends’ influences can be largely explained by their specific developmental stage. Adolescents become increasingly concerned with descriptive (everybody does it) and injunctive norms (everybody finds it okay) in their environment and find higher emotional reward in social conformity with such norms [34,35]. In this developmental stage, adolescents spend significantly more time with peers, and the peer group increases due to the frequent changing of classes and increased time spent out of classes with peers [36,37]. Interventions using techniques to train resistance skills against peer pressure in regard to risk health behavior might thus be a valid method for prevention, and resistance skills are included as component in so-called life-skills programs. However, simply the increase of and propensity to social cohesion during adolescence might explain increased substance use alone [38,39], without an explicit role of “peer pressure”. Several evidence-based prevention programs, such as the Unplugged study [40], focussing on developmental components (i.e., skills and competences) and normative beliefs are available in Europe, yet need larger implementation.

Furthermore, it might be of relevance to tackle possible misperceptions about peer substance use behavior. Our study showed that especially participants who perceived that their peers engaged in risky alcohol and cannabis use showed a higher likelihood to report drunkenness episodes or the use of cannabis on their own. Perceiving most or all of their peers to be risky alcohol or cannabis users seems to be an exaggerated perception—as already described in other studies [28,30]—as the prevalence estimates in ESPAD suggest that the majority does not engage in risky substance use behavior. The strong relationship of descriptive norms found with risky substance use in this analysis can be explained by two alternative theoretical frameworks with the respective options for prevention strategies, which are complementary to each other. One, in line with Social Norms Theory, argues that the (mis)perception of the behavior of relevant others (“peers”) influences own behavior, as explained above [22]. Prevention responses responding to this assumption are the so-called social norms interventions: they aim at correcting the frequent overestimation of peer substance use among school and university students [41].

In Denmark, the country that has been found to show the highest drunkenness rates among school students in our study, an intervention was tested focusing on drinking behavior in this specific target group. School students that received the intervention showed decreased overestimations of peer use and alcohol-related harms compared to control. Effects on the individual drinking behavior were only found in the sub-sample of pupils who stated that it would be okay if they drank more [42]. Overall, the evidence for the effectiveness of such approaches in Europe is still low [43], and more research among adolescents is needed. To our knowledge, there are no studies available focusing on effects of social norms interventions on cannabis use in European school students.

An alternative explanatory model virtually inverts the assumed chain of events: when school students fill in the ESPAD questionnaire, they report on their own use during the last year/last month, but also on the perceived use of their peers in the current moment. Therefore, the very procedure of data collection reflects that consumption behavior precedes the descriptive norm. The reasoning is in line with the postulation that “attitude follows behavior” [44], suggesting, in this case, that substance-using school students select their peers according to their own behavior and therefore perceive most of their peers as having risky alcohol or cannabis use (norm-narrowing). Under this scenario—where substance-users have been chosen to be peers—there is no normative fallacy to be corrected by social norms interventions. This perspective is underpinned by a recent study, where 39 participants with a cannabis disorder had to nominate close peers and estimate the level of substance use of these. The estimates were accurate, which the authors interpret as challenging the “false consensus theory”. The findings, however, rather support the hypothesis that people quite accurately assess the level of use of close peers whom they have selected themselves [45].

The adequate response principle under this hypothesis appears to be environmental prevention, which aims at reducing the opportunities for undesirable behavior (here: risky alcohol and cannabis use) to occur. This, in turn, reduces the acceptability, normality, and visibility of these behaviors and, consequently, norms, beliefs, attitudes, and values surrounding the undesired behavior also change. Complementary to skills training and the correction of cognitive fallacies, the modus operandi here is to change and sustain modified behavior—often inconspicuously—by altering the physical, economic, and regulatory aspects of the environment in which a certain behavior occurs [24]. Physical (e.g., outlet distance to schools), economic (e.g., lower prices for non-alcoholic drinks), and regulatory (e.g., substance use policies in schools and age checks in outlets) environmental prevention interventions at local level should consistently be improved.

Next to perceived substance use of peers, poor parental support was also found to be a significant risk factor for alcohol and cannabis use among school goers. This is in line with research findings suggesting that parental support belongs together with parental monitoring, parent–child relationship quality, parental support, and parental involvement to the longitudinal protective factors for both alcohol initiation and levels of later alcohol use/misuse that are modifiable, alongside with parental provision of alcohol, favorable parental attitudes towards alcohol, and parental drinking as risk factors [46]. The Monitoring the Future study conducted in the US showed that parental monitoring was one of the strongest predictors of substance use among school students, and it was found especially protective against substance use for high-risk-taking adolescents [47]. Consequently, selective preventive efforts are required. Several evidence-based interventions are available that address these factors [48,49].

Poor academic performance was found to be associated with risky alcohol as well as with cannabis use behavior in this analysis. There is additional evidence for a reciprocal association between academic performance and parental support [50], also across cultures [51]. Both factors that were examined in our study therefore suggest further implementing interventions to improve parental skills as an additional preventive strategy.

Due to the cross-sectional design, we cannot determine causal inferences between academic performance and substance use. Other studies in this field show a clear negative relation between school performance and substance use, but assume a reverse association [52,53]. A study measuring trajectories of academic self-esteem in a younger target group (13 to 15 years), however, showed that substance use is associated with persisting or increasing perceptions of academic failure. School students who perceived that their academic performance increased during the survey period or remained at a good level showed a smaller increase in substance use behavior between the survey time points [54]. In regard to cannabis, a European prospective cohort study suggested that adolescent cannabis use is not associated with educational performance, after adjustment for potential confounders such as smoking [55]. A longitudinal French study [56] showed that over three birth cohorts that less educated cannabis use initiators more often shifted to daily use than the most educated, thus giving support to academic underachievement predicting more cannabis use. Interpreting our data in the context of these additional studies warrants the need for education policies that are committed to providing particular support to school students with less academic success and hence less engagement with school. It seems important to also consider such policies as prevention interventions.

In general, it is common for schools in Europe to employ alcohol and drug policies to regulate access to substances on school grounds or events and set standards for the acceptability of alcohol and drugs in school. However, a study from the US and Australia highlighted that the means of their implementation is crucial for influencing substance use. Evans-Whipp et al. [57] found that lax policy enforcement was associated with an increased likelihood of drinking. Counselling for alcohol policy violators reduced the likelihood of risky alcohol use. However, perceptions of harsh penalties were unrelated to alcohol use.

Our study demonstrates that ESPAD provides a valuable data source to identify factors that are found to be associated with alcohol and cannabis use among adolescents and which can be targeted by prevention strategies. The multi-national perspective offers the opportunity to tailor prevention strategies to the needs of specific European regions. Morgan et al. [58] already addressed this issue when analyzing 1995 data from ESPAD across the then 26 participating countries. Morgan et al. stated that most of the research about risk factors for substance use employed individualistic research designs, only differentiating between adolescents who use various substances and those who do not. Their study results indicated that some results from the individualistic tradition are confirmed in cross-cultural comparison, while other results are less so [58].

The focus should arguably now turn to the question of how our findings might be used as a basis to improve preventive interventions in the future.

The strengths of this study are the sample size and the multinational standardized data collection. As ESPAD data are collected on a regular basis, they can give an insight in changes and trends over time. However, the findings of our study should be interpreted with several caveats. It should be noted that the German ESPAD survey covered only five of the 16 federal states, and the UK survey had low participation of invited schools in 2011. In general, results might not be fully generalizable to all school students of the participating countries. Furthermore, the same questions were not integrated into the respective questionnaires in all countries. Even though most of the questions were asked in all countries, heavy drinking and personal adherence to rules were not. We have therefore decided not to select binge drinking as a proxy for risky alcohol use. Furthermore, as the personal adherence to rules was not addressed in questionnaires in Western Europe, no European area-specific estimate for Western Europe could be generated in stratified analyses. Moreover, ESPAD is based upon self-reported data, and an under- or overestimation of risky substance use behavior due to social expectation bias cannot be ruled out. Furthermore, the ESPAD survey does not obtain information on when exactly, on what specific occasions, and which kind of alcoholic beverages were used. Thus, we cannot draw any conclusions as to whether substances were used in a nightlife context or in everyday life. This information should be included in future studies, since other studies from the US showed that assessing this kind of information (i.e., the frequency of evenings out with friends (unsupervised by adults)) regarding alcohol and substance use is important [59]. Additionally, due to the research design and the asked questions in ESPAD, we cannot say whether the perception of peer use follows personal behavior (norm-narrowing), or it is an overestimation of peer use, or both. Since the perception is the most important associated factor, it should it should be investigated in more depth in future studies.