The use of alcohol among adolescents in Denmark is one of the highest in Europe, which applies both to quantities consumed at each drinking session as well as to the frequency of sessions [1–3]. Approximately 37 % of Danish pupils aged 15–16 years reported drunkenness in the last 30 days, while the European average for this age group is 17 % [2]. Similarly, the percentage of binge drinkers in this age group, i.e. those who have consumed five or more drinks at one drinking session in the last 30 days, is high with 60 % for boys and 53 % for girls, respectively [2]. Regarding other drug use, 6 % of Danish adolescents reported cannabis use within the last 30 days and an average of 5 % reported lifetime use of illicit drugs other than cannabis. Hence Danish adolescents reported a similar prevalence compared to adolescents in other European countries, where the average in 36 countries was 7 % and 6 %, respectively. Further experience with various drug use other than alcohol is more frequently reported among boys [2, 4].

Excessive alcohol use has serious short-term consequences for a number of young Danes. Among other harmful consequences, one third of boys and girls performed poorly at school due to drinking. Furthermore, a proportion of 17 % of boys have gotten into fights with peers as a result of alcohol use [5]. Adolescents who use alcohol, tobacco or other drugs achieve lower grades, have more negative attitudes towards school and exhibit increased absenteeism [6, 7]. A large longitudinal study in the US concluded that by the end of high school, alcohol consumption predicted declining socio-economic functioning with negative implications for adolescents’ academic grades [8]. Additionally, an increased likelihood of harmful drinking in adolescence has been described as contributing to long-term consequences with regard to harmful drinking as an adult [9]. It has also been observed that an early debut of alcohol drinking increases the risk of alcohol dependency and alcohol related diseases later in life [10, 11]. Thus, it can be argued that decreased substance use would reduce the risk of substance related events and other harmful behaviour, and potentially improve health and life prospects among young people.

Individuals, particularly young people, are strongly influenced by their perceptions of the behaviour and attitudes of those around them, which has been suggested by social comparison theory [12, 13]. However, it has also been demonstrated that individuals overestimate the risk behaviours of their peers (descriptive norms), and also how accepting their peers are of such behaviours (injunctive norms). The origins of this finding derive from evidence exploring alcohol use among students in the American college system [14–19]. Yet misperceptions of peer alcohol and other related substance use have also been documented in school and college students across a number of European countries [20–23].

This tendency towards misperception has serious consequences as individuals are likely to be driven to match what they perceive to be the norm amongst their peers, as suggested by psychological theories of behaviour such as the Theory of Planned Behaviour [24]. It is also known that individuals often lack awareness of how easily influenced they really are by the norms of a particular group [25]. Other social psychological research investigating factors such as attribution bias helps to explain how people tend to perceive those around them as behaving in a more risky way than themselves [26]. Such misperceptions may also be reinforced by media rhetoric which frequently perpetuates negative stereotypes. For instance, media portrayals in Denmark often describe adolescents and young people as regular and frequent heavy drinkers, despite the fact that in reality the majority of Danish adolescents do not binge drink on a regular basis [27].

The findings that reveal the presence of such misperceptions has become the basis for an approach towards behaviour change and prevention known as the social norms approach. This approach works on the premise that if misperceptions about a group norm are challenged, the social pressure on the individual to behave in the respective risky manner will decrease and result in the promotion of more positive, healthy behaviour [28]. Similarly, the social norms approach can be used to challenge misperceptions that people may hold regarding the attitudes of their peers, such as an individual perceiving their peers to support cannabis use to a higher extent than they actually do [29]. The social norms approach differs from other prevention approaches because it does not rely on negative or fear based imagery and it does not contain any moralistic messages about how the target population should behave or what their attitudes should be. Instead, it aims to empower individuals through promoting informed decision making by encouraging them to question the negative misperceptions they hold about their peers [22]. In conclusion, the social norms approach differs fundamentally from many other forms of prevention and behaviour change interventions by focusing on the positive behaviour of the majority, rather than on the negative behaviour of the minority.

It is increasingly evident from various studies that mass media campaigns with a moralistic or fear arousing focus have modest effects on young people and a few studies even report their negative effect. These counter-productive interventions often include a single component of many, and focus on the negative health consequences of a risk-behaviour [30–32]. When using social norms marketing to influence the behaviour of young individuals, it is essential to ensure sufficient repetition of the message through different channels such as posters, websites/web applications, flyers, e-mail messages and newspaper editorials. Furthermore, the setting in which the social norms marketing campaign is received should meet the needs, expectations and cultural requirements of the target group [30, 33]. In their umbrella review, Jepson et al. [32] found that the most effective interventions included school-based activities promoting positive behaviours and social norm marketing has been shown to be an effective method in decreasing alcohol consumption among adolescents [14, 15].

A European study with 170 intervention and control schools investigated the effectiveness of a substance abuse prevention programme with a social norm correction. Results showed “a persistent positive effect over 18 months for alcohol abuse and for cannabis use, but not for cigarette smoking” [23]. The authors explained the lack of effect for smoking by stating that accumulating evidence illustrates how dependency in adolescence can occur following the sporadic use of tobacco. Cigarette smoking may also be a normative behaviour to a larger extent compared to episodes of drunkenness or illicit drug use in the age groups studied. However, this European study did not include Danish schools.

In Denmark, intervention studies based on social norms theory are sparse. A smaller scale study called the Ringsted trial, which partly used social norm approaches at primary schools, could demonstrate that the social norms intervention reduces misperceptions of descriptive norms related to smoking, alcohol, drug use, crime and bullying, but the sample size was too small to observe significant effects on behaviour [34]. Another intervention study using the social norms approach to reduce teenage smoking has been evaluated in the municipalities of Frederikssund and Bornholm among 6 graders, (“Alle de andre gør det”) resulting in some positive effects on perceptions. However, the study design did not allow for any conclusions on the effectiveness of the approach in Denmark [35]. Similarly, a qualitative survey in 2011 showed that 67 % of the Danish municipalities had adapted the social norms theory and tailored it to each of their school interventions. Unfortunately, neither of the designs allowed any measure of effectiveness [36].

The scientific evidence to date illustrates the need to strengthen effective interventions targeting school aged children in Denmark in order to positively influence their perceived and actual alcohol and other drug (AOD) use. As a result, this paper describes the design of the school-based cluster-randomized trial The GOOD life (In Danish: Det GODE liv) which aims to reduce AOD use and related harm among Danish adolescents. The trial is funded as the research project “De gode liv mellem de unge” by the Danish foundation TrygFonden.