In routine school settings, this brief curriculum-integrated intervention was associated with a short-term increase in a content-specific measure of cannabis risk knowledge assessed two weeks after the final session. Because this was a single-group pre–post study, the observed change cannot be attributed exclusively to the intervention and may also reflect testing effects, short-term recall, item familiarization, maturation, or other uncontrolled influences. Accordingly, the findings should be interpreted as documenting short-term within-sample change in a proximal cognitive outcome, rather than as evidence of intervention effectiveness or superiority over other preventive approaches. This interpretation is consistent with reviews showing that universal school-based prevention programs often have small or null effects on cannabis use, whereas interactive and higher-dose skills-based programs tend to show more consistent benefits [13,20,25,26,27,28].

The main contribution of this study is to quantify, under routine school implementation and with a total dose of three hours, the magnitude of short-term cognitive change in specific cannabis-related knowledge. This provides a pragmatic reference point for future controlled and implementation-focused evaluations of brief school-based prevention formats.

The magnitude of change should be interpreted in light of the assessment timing and the type of outcome measured. Because the posttest was administered two weeks after the final session, the findings likely reflect short-term recall or near-term retention of intervention content rather than sustained knowledge consolidation. In addition, the primary outcome was measured using an ad hoc scale developed to reflect the intervention’s specific content. Although this may increase sensitivity to detect near-term change, it limits comparability with other studies and raises the possibility of content alignment or teaching-to-test effects. Because no psychometric evaluation was performed, the reliability, validity, interpretability, and responsiveness of the measure remain uncertain. A recent systematic review in adolescents indicates that higher cannabis-related knowledge and higher perceived risk are often associated with lower current use and lower intentions to use, supporting these constructs as proximal prevention targets [7]. Therefore, the observed change should be interpreted as an intermediate cognitive outcome only, without conclusions about prevention impact, behavioral change, or durability.

Importantly, longitudinal research suggests that perceived risk is not only a predictor of later cannabis use but also a consequence of use: initiation and continued use can lead to decreases in perceived risk over time, reinforcing the need for repeated messaging and components that target normative beliefs and risk appraisal. In Spain, national survey analyses similarly show that lower perceived risk and greater perceived accessibility are associated with a higher likelihood of cannabis use among adolescents, indicating that prevention content may benefit from explicitly addressing both risk perception and perceived availability [29,30]. Educational content also needs to keep pace with the rapidly changing cannabis landscape in Europe. Recent monitoring describes increases in THC potency, diversification of consumer products (e.g., vaping products, edibles, and high-potency concentrates), and the emergence of semi-synthetic cannabinoids, all of which can complicate adolescents’ understanding of dose, routes of administration, and risk. This supports the value of curricula that move beyond “cannabis” as a single product category and include product- and harm-relevant information aligned with current epidemiological and market indicators [31]. In practice, these findings support considering brief curricular interventions as pragmatic approaches that warrant a further evaluation of early cognitive mediators, although studies with comparator groups and follow-up are required to assess the persistence of change and its relationship to behavioral outcomes [3,18].

Secondary analyses were intended only to describe the sample context and explore possible associations with selected family and clinical factors. Given the small cell frequencies in several categories, these findings should be interpreted exclusively as exploratory and hypothesis-generating. In particular, the observed relationships between reported parental use and student cannabis and amphetamine use, as well as the association between mental health follow-up and non-daily amphetamine use, should not be given inferential weight. Nevertheless, the patterns observed for parental cannabis use are consistent with previous evidence linking parental cannabis use with a higher likelihood of cannabis initiation and use among offspring [32,33].

The strengths of this study include the evaluation of a brief preventive intervention delivered under routine school conditions, integrated into the curriculum and implemented in three schools using standardized classroom sessions led by health professionals. The paired pre–post design allowed for the estimation of short-term change in a relevant cognitive outcome in an adolescent sample. However, several limitations constrain interpretation. First, the absence of a control group prevents attributing the observed change exclusively to the intervention and does not allow alternative explanations, such as history, maturation, testing effects, or item familiarization, to be ruled out. Second, implementation in a single municipality limits the direct generalizability of the effect magnitude. Third, because the total number of eligible students invited and the reasons for non-participation were not systematically recorded, the participation rate could not be estimated, and potential selection bias cannot be excluded. Fourth, evaluation focused on a short-term cognitive outcome without longitudinal follow-up or the measurement of behavioral change. Finally, although the intervention was standardized through a common script and materials, formal implementation measures such as fidelity, adherence, quality of delivery, and participant engagement were not collected; therefore, the consistency of delivery cannot be verified, and feasibility or scalability should not be inferred from these data alone. Secondary analyses should also be considered strictly exploratory because of the limited sample size and small subgroup frequencies.

Future studies should use controlled designs, longer follow-up, and standardized or psychometrically evaluated outcome measures to assess whether short-term changes in knowledge are sustained and whether they are associated with trajectories of use during adolescence. Process and implementation measures, including fidelity, received dose, and participant engagement, would also strengthen interpretation under routine conditions [15,28,34,35]. Recent school-based approaches using digital delivery, harm reduction framing, or drug literacy components may offer useful directions for future evaluation [21,22,23].