Cannabis is the most commonly used illicit psychoactive substance among European and North American adolescents. The 2017/2018 Health Behaviour in School-aged Children (HBSC) study (Inchley et al., 2018) showed that the lifetime prevalence of cannabis use among 15-year-old school students ranged from about 2 % in Azerbaijan and Kazakhstan to 25 % in Bulgaria, with a 43-country average of about 13 % (Jo et al., 2017). Evidence indicates that early and frequent cannabis use can be harmful to health and mental health (Volkow et al., 2014, Albaugh et al., 2021). Early, heavy, and accelerated use are related to problems such as impaired brain development, low height and weight, short-term memory loss, and other cognitive disorders (Van Ours & Williams, 2009), deterioration of school performance and dropout (Bachman et al., 2007), risk taking, aggression and delinquency (Griffith-Lendering et al., 2011), depression and anxiety (Griffith-Lendering et al., 2011), and the development of the so-called lack of motivation syndrome (Ding et al., 2014). Its use can also trigger psychosis among those who are vulnerable to this disorder (Casadio et al., 2011). Cannabis use is often part of a more extensive pattern of risk behaviors: it goes hand in hand with, among others, more smoking, (binge) drinking, and drunkenness (Charrier et al., 2019).

In the first decade of 2000, decreases in cannabis use were observed across many Western countries; however, this downward trend has come to a halt in most countries. The overall prevalence of lifetime and last 30-day use of cannabis among secondary school students has remained stable in Europe and Canada between 2014 and 2018 (Jo et al., 2017, Inchley et al., 2016). Stable trends in cannabis use but increases in some regions – South Europe and the Balkans – were also found in studies of the European School Survey Project on Alcohol and Other Drugs (ESPAD) (Kraus et al., 2018).

Consumption may have declined or stabilized in most regions of the Western world, but cannabis is still a widely used illicit drug, with a substantial minority of young people consuming it on a regular basis, from an early age on. Furthermore, population surveys show that the perception of the risk of cannabis has declined significantly (Harel-Fisch et al., 2015), and in many Western countries its use is “normalized” (Sznitman et al., 2015). Other studies suggested that cannabis use has “trickled down” from richer to poorer countries, and within these countries, from adolescents with higher family affluence to peers with lower family affluence (ter Bogt et al., 2014).

From a public health perspective, monitoring trends in adolescent substance use is essential. Health surveys have been shown to be a valuable tool to evaluate trajectories of continuity or change in health outcomes and are crucial for the (early) detection of changes over time. Not only monitoring but also predicting trends can have great value in shaping substance use interventions and policies. Comparing the actual data collected (and used for forecasting) with the forecast data can provide insight into the effectiveness of current policies and health promotion interventions. Pullum (2022) noticed that earlier rounds of a specific survey can be used to predict the levels of health outcomes in later rounds of the same survey. Indeed, predictions are built on the notion of continuity of underlying processes, and changes in expected values of an outcome may be indicative of modifications of health determinants.

Recent evidence showed that relatively simple methods for predicting future trends in health issues can be highly accurate. For example, in an HBSC-study, alcohol use was predicted based on observed trends from past data, showing consistent patterns between estimated and actual prevalences across countries (Charrier et al., 2022).

The HBSC study serves as an important source for several indicators of cannabis use, relevant to both regional and cross-country assessments of health-related behaviors among adolescents. The present study aims to summarize HBSC cannabis consumption data from the past two decades and project trends among 15-year-olds in the HBSC 2021/2022 survey sample (data still under embargo). Moreover, since between the last two HBSC waves (2017/2018 and 2021/2022) the COVID-19 pandemic has heavily influenced adolescents’ lives and probably also their risk behaviors, including cannabis use, the discrepancies between the predicted and observed data in 2022 could help generate hypotheses about the effect of the pandemic and the measures taken to contain it. In fact, the studies to date have failed to uniquely capture this aspect, presenting mixed results.