Preventing teenagers’ use of cannabis with school interventions

A recent study investigated the efficacy of high school drug prevention programs

Attitudes towards cannabis have changed drastically in the past few years. The most notable aspect relates to the perception of drug safety, which is taken for granted by an increasingly larger set of the populace. Included in this group are teenagers, who might be particularly vulnerable to the disruptive effects of cannabis on neural development and cognition.

Data from 2015 suggests that up to 30% of U.S. teenagers from grades 8 to 12 have experimented with cannabis, with past-month use and daily use surpassing that of tobacco. In Canada there is a similar picture, as governmental data indicates that 29% of youths aged 15 to 19 have used the drug, with the average user being 15 years old at the time of initiation.

The educational community has not been impervious to these trends. Today, several interactive programs are being implemented in the classroom by teachers, health practitioners, older peers and law agents. The main goal is to reduce current and future cannabis use by informing students about the risks of consumption and teaching them skills to resist peer pressure.

Project ALERT brochure (RAND corporation)

Does it work?

Dr. Steven Lize and seven collaborators from the University of South Carolina attempted to answer this question. To accomplish this, they reviewed the evidence from the best intervention programs conducted in the U.S. and Canada. Their report has been published in the Journal of Prevention Science, where it can be freely accessed.

Thirty studies that included appropriate control groups (no programming, health information or treatment as usual) and comparable methodologies were selected. In most cases, the program was implemented in schools and comprised an average of 17 sessions. Some also included ‘booster sessions’ up to six months or a year later.

Among the interventions that measured changes in cannabis use (usually through self-report), two achieved a medium effect, twenty-two had small effects, two had no effect and four had negative effects that favored the control group. Pooled together, the interventions converged to a significant effect size of 0.07*.

There were fewer interventions aimed at promoting the ability to refuse other people’s offers to use cannabis or to change individuals’ intentions to use it in the next week or month. These had smaller effects that, when merged, failed to attain statistical significance.

Further analysis did not reveal any differences between studies according to the type of control treatment used, nor any evidence for study publication bias. The only aspect that systematically altered the efficacy of an intervention was the nature of the instructor—teachers and health practitioners fared better than the alternatives.

Interestingly, the only case where the intervention was given by a peer (with the presence of adults) led to negative effects in reported cannabis use. Although peer interventions should not be crossed out immediately, this finding calls for a re-assessment of this type of intervention.

In sum, the combined evidence suggests that interactive school programs can be effective in reducing adolescent cannabis use, but to a limited extent. The authors argue that this small statistical effect could still translate to considerable practical effects, especially if the programs get adopted by a large number of schools.

* If the intervention had the goal of increasing students’ IQ, an effect size of 0.07 would mean that the treatment group had gained, on average, 1.05 IQ points.

Featured image via Wikipedia.

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  1. Maxcatski Reply

    Wow, we suddenly leapt from an article about school interventions to a conclusion about a drop in IQ! Firstly, an intervention effect of .07 is NOT significant given the likely errors and self-reporting. Secondly, a drop of one point in IQ is scarcely measurable and also NOT significant. And, thirdly and most important, who decided the consuming cannabis was a bad thing? Regardless of age, consuming cannabis is preferable to consuming alcohol and tobacco. Teenage behavior is not going to stop regardless of the number of school interventions. These will do more harm than good once the students wake up and recognize they have been lead astray. And how did they calculate that drop in IQ anyway? Sounds like bullshit to me!