Combined online prevention of substance use, depression, and anxiety led to increased knowledge of alcohol, cannabis, and mental health, reduced increase in the odds of any drinking and heavy episodic drinking, and reduced symptoms of anxiety over a 30-month period. These findings provide the first evidence of the effectiveness of an online universal school-based preventive intervention targeting substance use, depression, and anxiety in adolescence.

Between Sept 1, 2013, and Feb 28, 2014, we recruited 88 schools (12 391 pupils), of whom 71 schools and 6386 (51·5%) pupils were analysed (17 schools dropped out and 1308 pupils declined to participate). We allocated 18 schools (1739 [27·25%] pupils; 1690 [97·2%] completed at least one follow-up) to the substance use condition, 18 schools (1594 [25·0%] pupils; 1560 [97·9%] completed at least one follow-up) to the mental health condition, 16 schools (1497 [23·4%] pupils; 1443 [96·4%] completed at least one follow-up) to the combined condition, and 19 schools (1556 [23·4%] pupils; 1513 [97·2%] completed at least one follow-up) to the control condition. Compared with controls, the combined intervention group had increased knowledge related to alcohol and cannabis at 12, 24, and 30 months (standardised mean difference [SMD] for alcohol 0·26 [95% CI 0·14 to 0·39] and for cannabis 0·17 [0·06 to 0·28] at 30 months), increased knowledge related to mental health at 24 months (0·17 [0·08 to 0·27]), reduced growth in their odds of drinking and heavy episodic drinking at 12, 24, and 30 months (odds ratio for drinking 0·25 [95% CI 0·12 to 0·51], and for heavy episodic drinking 0·15 [0·04 to 0·58] at 30 months), and reduced increases in anxiety symptoms at 12 and 30 months (SMD −0·12 [95% CI −0·22 to −0·01] at 30 months). We found no difference in symptoms or probable diagnosis of depression. The combined intervention group also showed improvement in alcohol use outcomes compared with the substance use and mental health interventions and improvements in anxiety outcomes when compared with the mental health intervention only.

We did a multicentre, cluster-randomised controlled trial in secondary schools in Australia, with pupils in year 8 or 9 (aged 13–14 years). Participating schools were randomly assigned (1:1:1:1) to one of four intervention conditions: (1) Climate Schools–Substance Use, focusing on substance use only; (2) Climate Schools–Mental Health, focusing on depression and anxiety only; (3) Climate Schools–Combined, focusing on the prevention of substance use, depression, and anxiety; or (4) active control. The interventions were delivered in school classrooms in an online delivery format and used a mixture of peer cartoon storyboards and classroom activities that were focused on alcohol, cannabis, anxiety, and depression. The interventions were delivered for 2 years and primary outcomes were knowledge related to alcohol, cannabis, and mental health; alcohol use, including heavy episodic drinking; and depression and anxiety symptoms at 12, 24, and 30 months after baseline. This trial is registered with the Australian New Zealand Clinical Trials Registry (ACTRN12613000723785) and an extended follow-up is underway.

Substance use, depression, and anxiety in adolescence are major public health problems requiring new scalable prevention strategies. We aimed to assess the effectiveness of a combined online universal (ie, delivered to all pupils) school-based preventive intervention targeting substance use, depression, and anxiety in adolescence.

In a large, school-based, cluster-randomised controlled trial, we aimed to investigate the effectiveness of a combined approach to the prevention of primary substance use (specifically alcohol and cannabis), depression, and anxiety. Research hypotheses were prespecified in the protocol.

The Climate Schools–Combined programme incorporates two proven interventions: the Climate Schools–Substance Use course and the Climate Schools–Mental Health course. Using an online format, these courses are designed to overcome common barriers to effective implementation (eg, the substantial time and costs involved in delivering interventions face-to-face).The Climate Schools programmes are built on a social influence approach, which imparts information in an engaging and youth-focused way using cartoon storylines. The interventions are accessed online by students to maximise engagement and implementation fidelity.Classroom activities and lesson summaries complement the online storylines and are designed to reinforce learning. The Climate Schools–Substance Use course has shown effectiveness in increasing alcohol and cannabis knowledge, and reducing the uptake and heavy episodic use of alcohol up to 24 months post baseline.The Climate Schools–Mental Health course has shown substantial improvements in anxiety and depressive symptoms after intervention.

These findings are consistent with modern dimensional approaches to psychopathology, in which an individual's propensity to develop all forms of psychopathology is summarised in terms of a unidimensional p factor. The identification of the p factor offers new conceptualisations for universal prevention,particularly in childhood and early adolescence, when causal risks are transdiagnostic and disorders have not yet emerged.The p factor summarises commonalities across substance use, depression, and anxiety that might explain the secondary benefits gained from prevention programmes focused on one condition. However, prevention approaches that explicitly incorporate and maximise this potential secondary benefit have not been developed.

Interventions that are delivered in schools have the potential to prevent, delay onset, reduce prevalence, and reduce the effect of substance use, depression, and anxiety at a population level. Individual universal school-based programmes, delivered to all adolescents, regardless of the level of risk, have shown small-to-moderate reductions in substance use,depression, and anxiety.These universal prevention programmes have traditionally focused on single disorders. Despite this focus, these programmes have been shown to have disorder-specific (primary) effects as well as more generalised (secondary) effects on untargeted, putative distal outcomes. For example, a prevention programme focusing on adolescent depression reported reductions in depressive symptoms and reduced substance use up to 2 years after intervention.Furthermore, programmes to prevent substance use have effects that extend beyond substance use outcomes. For example, the Preventure programme is a selective personality-targeted programme to reduce adolescent substance use that has proven benefits in reducing mental health symptoms and bullying.In addition to reducing substance use, universal substance-use prevention delivered in adolescence has been shown to associate with reduced depressive symptoms in young adulthoodand psychological distress more broadly.

School-based programmes to reduce and prevent substance use in different age groups: what works for whom? Systematic review and meta-regression analysis.

The Climate Schools–Combined intervention offers an interactive, scalable, and efficient approach to preventing the substantial burden of disease attributed to substance use and related disorders and mental ill health. However, longer-term follow-up is needed into early adulthood, when most people are likely to have their first onset of disorder. Extended follow-up would also allow for a more robust examination of alcohol-related harms, which traditionally increase during the adolescent years as exposure to alcohol increases.

We assessed the first online universal prevention programme to target substance use, depression, and anxiety in adolescents within a combined prevention model, which has the potential to maximise prevention effects by capitalising on primary and secondary benefits. The Climate Schools–Combined programme incorporates two proven interventions; the Climate Schools–Substance Use course and the Climate Schools–Mental Health course. Using an online format, these courses were designed to overcome common barriers to effective implementation (eg, the substantial cost and time involved with delivering face-to-face interventions). Our findings showed broad support for the effectiveness of the combined intervention in increasing knowledge, reducing increases in anxiety, and reducing increases in the odds of alcohol use compared with school-based health education as usual and the stand-alone mental health course. However, we found less evidence for the superiority of the combined intervention compared with the stand-alone substance use course.

Scalable innovative prevention approaches are needed to address the substantial burden of disease attributed to substance use, depression, and anxiety across the globe. Individual, universal, school-based programmes have shown small-to-moderate reductions in substance use, depression, and anxiety during adolescence. These universal prevention programmes have traditionally focused on single disorders and have had disorder-specific (primary) effects as well as more generalised (secondary) effects on untargeted, putative distal outcomes—eg, substance use programmes can reduce mental health problems and mental health programmes can reduce substance use. These findings are consistent with modern dimensional approaches to psychopathology, in which an individual's propensity to develop all forms of psychopathology is summarised in terms of a unidimensional p factor. However, prevention approaches that explicitly incorporate and maximise this potential secondary benefit have not been developed.

Substance use, depression, and anxiety are the leading causes of disability among young people in high-income countries.Onset of these conditions typically occurs during adolescence, with disability greatest among those aged 15–24 years.Importantly, substance use, depression, and anxiety frequently co-occur.Together, these conditions contribute to burden of disease and social and economic costs, largely due to the substantial health-care costs and time spent out of the workforce over a person's lifetime due to absenteeism or the inability to obtain work or undertake study and training during times of mental ill health.To alleviate this burden and improve the life trajectories of young people, we must intervene early, before patterns of substance use, depression, and anxiety are established and cause disability and harm.

The funder of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report. The corresponding author had full access to all the data in the study and had final responsibility for the decision to submit.

Additional sensitivity analyses adjusted for the covariates of sex and school type (public, private, Catholic), drinking at baseline, and possible diagnoses of depression and anxiety, covariates that were associated with missingness or were expected to be associated with the outcomes. After accounting for these predictors of missingness, and the observed outcome values, we assumed that the data met the missing at random (MAR) assumption. The multilevel mixed-effects models used in the analysis produce unbiased estimates under the MAR assumption. However, the sensitivity analyses showed little difference to the primary analyses in the size of effects or patterns of significance. Results of these sensitivity analyses are reported in the appendix (pp 3–12)

The fixed effects parameters included group and time as categorical predictors, as well as the group × time interaction. The control group was the reference level for group, and the baseline survey was the reference level for time. Random intercepts were included at the individual and school levels, as well as random slopes over time at the individual level to allow for a changing correlation between measurements of the same individual. Intervention effects were assessed on the basis of the group × time coefficients, representing the change from baseline for each intervention group compared with the control group. Data from all time-points (except for alcohol use and knowledge outcomes at the 15-month follow-up) were used in the statistical analysis. Specific comparisons of interest between groups were done for the 12, 24, and 30-month follow-up occasions. The 12-month follow-up time-point occurred after the delivery of the substance use intervention but before the delivery of the mental health intervention. The 24-month time-point occurred after the delivery of the mental health intervention. Comparisons were done using the Stata (version 15.1) margins command. Effect sizes were calculated as standardised mean differences (Cohen's d) for continuous outcomes and odds ratios (ORs) for binary outcomes, on the basis of group × time coefficients.

Outcomes were analysed using multilevel (generalised) linear mixed-effects models to account for the clustered structure of the data, with clustering occurring both within schools and within individuals.Linear mixed-effects models were used for continuous outcomes, and generalised linear mixed models with a logit link were used for binary outcomes. All analyses used an intention-to-treat approach, including all available measurements for all pupils, in the groups in which they were randomised.

We calculated sample size using a method to detect intervention by time interactions in longitudinal cluster-randomised designs.A minimum detectable effect size of 0·15 was chosen on the basis of reviews of previous universal anxiety, depression, and substance use prevention programmes.The required sample size for 80% power to detect between-group differences at the 0·05 level was seven schools per group, with 100 pupils in each school. This sample size also allowed for 10% dropout at the school level. The trial originally aimed to achieve this sample size within each of the three states to allow within-state comparisons.This size was not achieved; however, the total number of participants recruited across all states exceeded the required sample size and the trial was adequately powered to allow overall comparisons between the intervention groups.

School-based programmes to reduce and prevent substance use in different age groups: what works for whom? Systematic review and meta-regression analysis.

Symptoms of anxiety were assessed using the Generalised Anxiety Disorder Assessment 7-item version questionnaire.Scores ranged from 0 to 21, with scores of 10 classified as showing the possible presence of an anxiety disorder.

Depression symptoms were assessed using the adolescent version of the Patient Health Questionnaire-8 (PHQ-8).Scores on this scale ranged from 0 to 24, with scores of 10 or more representing the possible presence of a depressive disorder.

Alcohol use questions were derived from those used in previous climate schools trials.Participants were asked “Have you had a standard alcoholic drink in the past 6 months?”, responding either yes or no, and “How often did you have 5 or more standard alcoholic drinks on one occasion in the past 6 months?”, responding never, less than monthly, once a month, 2–3 times a month, weekly, daily, or almost daily. Heavy episodic drinking responses were converted to a dichotomous outcome (any heavy episodic drinking in the past 6 months or not).

Knowledge about alcohol was assessed using a 16-item scale adapted from the knowledge-of-alcohol index.Pupils responded “true”, “false”, or “don't know” to statements about alcohol—eg, “On average, younger people can tolerate alcohol more easily than older people,” giving scores (number of items answered correctly) between 0 and 16. Knowledge about cannabis was assessed with a 16-item scale used in previous climate schools trials,with “true”, “false”, “don't know” responses, yielding total scores between 0 and 16. Mental health knowledge was assessed using a 13-item multiple-choice scale, in which participants had to select the correct response for a statement or question—eg, “Which of the following is not a symptom of anxiety: dry mouth, feeling sick, sweating, dizzy, feeling sleepy?”

The primary outcomes were knowledge related to alcohol, cannabis, anxiety, and depression; alcohol use, including heavy episodic use; and severity of anxiety and depression symptoms. Ethics approval restrictions limited us from asking students about their cannabis use, which could therefore not be analysed.

Schools that were randomised to the active control condition delivered their usual health education classes over the year, including lessons on alcohol, drugs, and mental health. In Australia, this education is a mandatory part of the secondary-school health curriculum and all control schools reported delivering such lessons during this trial. Teachers were asked to provide details about the number and format of these existing lessons ( appendix p 1 ). Pupils were invited to participate in questionnaire assessments at baseline, then at 6, 12, 15, 18, 24, and 30 months after baseline (at the 15-month follow-up, only mental health-related measures were assessed; figure ). Pupils completed these self-reported questionnaires in classroom settings, either through an online questionnaire or paper surveys, and this was the only primary outcome measure used. A unique code was used to link the same participants' responses over time, while maintaining a de-identified dataset. Further details on implementation fidelity of the intervention and control groups are provided in the appendix (p 1)

In schools that were randomised to Climate Schools–Combined, pupils received the substance use programme one year and the mental health programme the next year.

Schools that were randomised to Climate Schools–Mental Health delivered the universal mental health course to their year 9 (Year 10 in Queensland) pupils during health education classes. This course is based on cognitive-behavioural principles and incorporates skill acquisition, psychoeducation, management of psychological symptoms, cognitive symptoms, behaviour, and additional skills that are specific to anxiety and depression. The course comprised six 40-min lessons aimed at reducing anxiety and depression, delivered in the same format as the substance use course. This intervention was delivered as a substitute to the schools' standard mental health education.

Schools that were randomised to Climate Schools–Substance Use delivered the universal substance use course to their year 8 students (year 9 in Queensland as students were 1 year younger in Queensland in this year level than in other states) during health education classes. The course comprised 12 40-min lessons aimed at reducing alcohol and cannabis use and related harms. Each lesson comprised a 20-min online cartoon component that was completed individually by pupils, followed by a 20-min activity delivered by the teacher, which reinforced the information in the cartoons and allowed for interactive communication. Teachers were provided with a hard-copy manual containing the activities, implementation guidelines, links to the education syllabus, and teacher and pupil summaries for each lesson. Teachers and pupils were provided with confidential login details to access the study website . Further details on the content of each lesson are described elsewhere ( appendix p 11 ).This intervention was delivered as a substitute to the schools' standard substance-use education.

Participating schools were randomly assigned to one of four study conditions: Climate Schools–Combined, Climate Schools–Substance Use, Climate Schools–Mental Health, or active control. Schools were assigned to the four interventions in a 1:1:1:1 ratio, using blocked randomisation, with blocks of four using the Stata ralloc command. The study biostatistician generated the random allocation sequence and the research coordinators allocated enrolled schools to the interventions per the random allocation sequence. Schools, pupils, and the research team were not masked to allocation.

The research protocol,including informed consent procedures and sample size calculations, was approved by the University of New South Wales, Curtin University, Queensland University of Technology Human Research Ethics Committees, the Western Australian and Brisbane Catholic Education Offices, and the New South Wales, Queensland and Western Australian Department of Education and Training.

We did a multicentre, cluster-randomised controlled trial in secondary schools in three Australian states (New South Wales, Western Australia, and Queensland). All pupils from participating schools in year 8 (New South Wales or Western Australia) or year 9 (Queensland), approximately 13–14 years old, were invited to take part in the trial. Only pupils who consented, and whose parents also consented to their participation, were eligible for inclusion in the trial.

Depression and anxiety outcomes are shown in table 7 . The change in PHQ-8 scores in the combined group was significantly lower than in the mental health group at 12 and 30 months, but not at 24 months ( table 8 ). The odds of a possible diagnosis of depression showed significantly lower relative change in the combined group than in the mental health group at 12 months.

Alcohol use data are shown in table 5 . Compared with the control group and the mental health group, the combined group's odds of drinking increased less over time, with significantly lower relative change in odds at 12, 24, and 30 months; and at 24 and 30 months when compared with the substance use group ( table 6 ). The odds of heavy episodic drinking in the combined group increased less than in the control and mental health groups at 12, 24, and 30 months, and less than in the substance use group at 30 months ( table 6 ).

Heavy episodic drinking was defined as drinking five or more standard drinks in a single occasion. ORs compared the relative change in odds from baseline for each group. OR=odds ratio.

Data are n/N (%). All outcomes refer to behaviours in the 6 months before the survey. Heavy episodic drinking was defined as drinking five or more standard drinks on a single occasion.

Knowledge about mental health increased more in the combined group than in the control group at 24 months, but not at months 12 and 30 ( table 4 ). The combined group also showed greater increases than the substance use group did at all follow-ups, and a greater increase compared with the mental health group at 12 months.

Knowledge outcomes for alcohol, cannabis, and mental health at each follow-up occasion are shown in table 2 . Increases in alcohol knowledge scores were greater in the combined and substance use groups than in the control group at 12, 24, and 30 months ( table 3 ). Cannabis knowledge scores increased more in the combined than in the control group at 12, 24, and 30 months ( table 3 ). The combined group also showed greater increases in alcohol and cannibas knowledge than the mental health group did at these occasions and had greater increases in cannabis knowledge from baseline than did the substance use group at 12 and 24 months, but not at 30 months ( table 3 ).

Full details of the multilevel mixed-effect models that were used for each outcome, including estimated coefficients and fit statistics, are reported in the appendix (pp 3–12)

Numbers of pupils followed up at each time-point are shown in the figure . 6206 (97·2%) of 6386 pupils completed at least one follow-up survey, and 3619 (56·7%) were absent for at least one follow-up. Boys were more likely to miss at least one follow-up than girls (1813 [62·9%] vs 1806 [51·6%]; OR 1·59, p<0·0001). Pupils in public schools were more likely to miss a follow-up compared with pupils in private or Catholic schools (2078 [61·9%] vs 1541 [50·9%]; 1·56, p<0·0001). The odds of missing at least one survey also increased among participants who reported drinking a full standard drink in the past 6 months at baseline (2·12, p<0·0001), among those who had a possible diagnosis of anxiety at baseline (1·45, p<0·0001), and among those who had a possible diagnosis of depression (1·41, p<0·0001).

The mean age of pupils at baseline was 13·5 years (SD 0·6), and 3502 (54·8%) were girls, which was similar to the general Australian population in 2014.Baseline characteristics of the participants are shown in table 1

18 schools (n=1739 [27·2%] pupils) were assigned to Climate Schools–Substance Use, 18 schools (n=1594 [25·0%]) to Climate Schools–Mental Health, 16 schools (n=1497 [23·4%]) to Climate Schools–Combined, and 19 schools (n=1556 [24·4%]) to the control group. In the control group, the number of lessons varied between schools (ranging from five to 20) with the average length of each lesson being 52 min.

Of the 556 schools in the three states that were approached to participate in the study, we recruited 88 schools (n=12 391 pupils) between Sept 1, 2013, and Feb 28, 2014. 17 schools dropped out and 1308 students declined to participate. The final sample consisted of 71 schools, with 6386 pupils consenting to participate ( figure ).

Discussion

This study is the first to show the effectiveness of a universal online combined approach for preventing alcohol use, anxiety, and depression in adolescence. Compared with pupils who received health education as usual (control group), pupils who received the Climate Schools–Combined intervention showed increased knowledge regarding alcohol and cannabis at 12, 24, and 30 months, and mental health at 24 months; less increase in their odds of any drinking and heavy episodic drinking at 12, 24, and 30 months; and reduced increases in anxiety symptoms at 12 and 30 months. Compared with pupils who received standalone prevention for substance use, pupils who received the combined intervention showed increased knowledge regarding cannabis at 12, and 24 months, and less growth in their odds of any drinking at 24 and 30 months. Compared with pupils who received standalone prevention for mental health problems, pupils who received the combined intervention showed increased knowledge regarding alcohol and cannabis at 12, 24, and 30 months; and mental health at 12 months; less increase in their odds of any drinking and heavy episodic drinking at 12, 24, and 30 months; reduced increases in anxiety and depressive symptoms at 12 and 30 months; and reduced odds of a probable diagnosis of depression at 12 months.

Our results support the effectiveness of the combined intervention compared with school-based health education as usual and the standalone mental health course. However, we found no significant evidence for the superiority of the combined intervention compared with the standalone substance use course. Not all comparisons were significant at all time-points, which could be related to a number of factors, including developmental age, the different lengths of the interventions, and the complex timing of intervention delivery across a 2-year period within the constraints of school-based delivery. Overall, the findings indicate support for generalised rather than specific effects of the intervention.

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et al. Evaluating the long-term effectiveness of school-based depression, anxiety, and substance use prevention into young adulthood: protocol for the Climate School Combined study. Aside from the reduced odds in probable diagnosis of depression between the combined and mental health groups, no differences over time were found in the odds of probable anxiety or depression diagnoses between the combined and any other group. This finding is not entirely unexpected given that diagnoses generally occur in early adulthood.This finding also highlights the need for longer-term follow-up of this sample into late adolescence and early adulthood, when most people are likely to have their first onset of disorder. Extended follow-up would also allow for a more robust examination of alcohol-related harms and cannabis use, which traditionally increase over the adolescent years as young people's exposure to alcohol and cannabis increases.To address this need, as well as the notable absence of rigorous data assessing the long-term effectiveness of prevention programmes,a longer-term follow-up study of this cohort is underway.This study aims to understand the longer-term effectiveness and cost-effectiveness of the combined intervention, up to 7 years after intervention, when the cohort will be aged 20 years.

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et al. Effectiveness of psychological and/or educational interventions in the prevention of anxiety: a systematic review, meta-analysis, and meta-regression. Nevertheless, our study addresses an important gap in the literature by investigating the effectiveness of the first universal online programme to concurrently target substance use, anxiety, and depression in adolescence. Although universal school-based programmes have shown small-to-moderate effects in reducing alcohol useand symptoms of anxiety and depression,prevention programmes traditionally ignore co-occurrence of these conditions. Additionally, although the capacity to deliver engaging and interactive interventions online has dramatically improved in the past decade, the benefit of online delivery is often overlooked, despite the advantages. The Climate Schools–Combined intervention offers an interactive, scalable, and efficient approach to preventing the substantial burden of disease attributed to substance use and related disorders, and mental ill health.

A main strength of this study is the large and diverse sample of independent private, government, and Catholic secondary schools from three states in Australia. Retention was high across the 30-month study period. Also, the cluster-randomised controlled trial design limited confounding effects and our statistical analyses used intention-to-treat analysis and controlled for individual-level and school-level clustering.

34 Del Boca FK

Darkes J The validity of self-reports of alcohol consumption: state of the science and challenges for research. Our study is not without limitations. Although we did not have corroborating information to support self-reported drinking outcomes, self-reported data were collected using structured and validated instruments, with clear guidance including Australian alcohol drinking charts. Within this context, self-report methods have been shown to be a reliable and valid approach to measuring substance use and mental health.Furthermore, although cannabis use was specified in the protocol as a primary outcome, ethics restrictions limited us from asking students about their cannabis use, which could therefore not be analysed. Future research should endeavour to include outcomes of cannabis, as well as other drug use.

Of the 556 schools approached to participate in the trial, 88 initially agreed, representing a participation rate of 15·8%. Students were generally from schools located in areas of above-average socioeconomic status, somewhat limiting the generalisibility of the findings. Furthermore, although over 97% of participants completed at least one follow-up session, those who missed a follow-up occasion were more likely to be male, to have reported consuming alcohol, and to have had a probable diagnosis of anxiety or depression at baseline. However, we found no evidence to suggest that this finding affected the results or interpretation of findings across groups.

16 Moffitt TE

Caspi A Psychiatry's opportunity to prevent the rising burden of age-related disease. Substance use, depression, and anxiety often share common risk factors. If we wish to address the major public health priority of substance use and mental ill health, continued research into novel and efficient programmes that target these problems together is crucial. Future research will address the need for longer-term follow-up to examine the effect of the intervention, because exposure to substance use and mental health symptoms increases over the transition out of secondary school. Similarly, longer-term follow-up might shed light on the mechanisms at play in the groups who received substance use or mental health interventions only, compared with the group who received the combined intervention. Future research might also focus on the differential effects these programmes have on underlying propensities for the development of manifest disorders, such as internalising, externalising, and general psychopathology (ie, the p factor). Novel methods for investigating treatment effects on these underlying dispositions have been developed, representing exciting new directions for assessing preventive interventions.

The Climate–Schools Combined intervention was found to be an effective model for increasing knowledge of alcohol, cannabis, and mental health; preventing alcohol use, including heavy episodic drinking; and reducing symptoms of anxiety and depression up to 30 months after baseline. These findings provide the first evidence, to our knowledge, of the effectiveness of an online, universal school-based preventive intervention, concurrently targeting substance use, depression, and anxiety in adolescence.