The impact of substance use on our society is reflected by its harmful effects. Smoking causes about 5 million deaths annually worldwide and the harmful use of alcohol results in approximately 2.5 million deaths each year. Among adolescents, risk behaviours such as smoking, alcohol and drug use are found to cluster with other risk behaviour such as unprotected sexual intercourse and antisocial or criminal behaviour. These (clustered) risk behaviours are associated with poor school results, and an increased risk of future morbidity and premature mortality. Starting to use alcohol, tobacco or drugs at a young age is a risk factor for the use or abuse as an adult. Prevention of substance use in young adolescents is therefore crucial in public health.
In 2003 Dutch adolescents were among Europe's highest alcohol consumers. Therefore, the political and social attention for harmful alcohol use among young people in the Netherlands has increased considerably. Since 2006, national drinking policies and school-based intervention programmes target adolescents and their parents with the message to postpone drinking until the age of 16. Other policies in the Netherlands aim at discouraging and postponing tobacco smoking by introducing an age limit [age 16] on buying tobacco products, by prohibiting advertising and by introducing smoking bans in public places. Policies on marijuana use, however, have not changed much and health promotion is relatively muted. Drug policy in the Netherlands mainly aims at controlling and reducing drug-related problems and has done so since its development in the mid-seventies of the previous century.
Recent national population studies showed promising trends on substance use among adolescents in the Netherlands. Between 2003 and 2009 lifetime and present (last month's) use of alcohol among Dutch adolescents strongly decreased among those under 16. Binge drinking among adolescents decreased between 2005 and 2007. Indeed, several studies support the idea that interventions addressing adolescents as well as their parents have been effective in preventing alcohol use in early adolescence. Between 2001 and 2009 decreasing trends were also found in smoking (lifetime and daily) and cannabis (last year) use by adolescents in the Netherlands.
Although the Dutch policies appear to be successful, the coherence in these policies and their evaluation is lacking; there is an alcohol policy, a tobacco policy, and a drugs policy. Policies are rarely developed and evaluated on a more general level. To date, there are no studies about whether a decrease in the use of one substance leads to an increase in the use of another. In other words, is there replacement? Does a reduction in the use of alcohol lead to more drug use? Do people who stopped smoking drink more in compensation? Personality characteristics and the developmental stage of adolescents are related to a need for risk or sensation seeking behaviour exercised in the form of different risky health behaviours dependent on opportunity. Therefore, in this paper, the emphasis is on the question to what extent behaviour and time trends in the use of different substances are interrelated. In this context we are furthermore curious to find out how trends develop in different subgroups. Does differential changes in different subgroups, as was also shown by others, lead to different replacements? Previous studies have shown that health promotion is effective in different ways and might need to target different aspects in different demographic groups. Therefore, we studied substance use by gender, age and educational level to get insight in possible effects of the campaigns. With this study we aim to provide points of reference for national policies or campaigns in other countries in or outside Europe.