Substance use is bidirectionally related to perceived harmfulness of its use. While adolescent tobacco, alcohol, and cannabis use have declined over time, little is known about perceived harmfulness trends across substances and frequencies of use. This study examines 20-year harmfulness perception trends of these substances.

Data from six survey rounds (n = 40,690) of a national cross-sectional school survey on substance use in the Netherlands were used to examine trends in harmfulness perception and substance use among 12- to 16-year-old secondary school students from 2003 to 2023. Logistic regression models were performed to examine these trends.

Students increasingly viewed tobacco and alcohol consumption as harmful (tobacco: occasional use: prevalence difference (PD) + 54.1 %, p < .001; daily use: PD + 2.5 %, p < .05; alcohol: ≥ 5 drinks every weekend: PD + 11.9 %, p < .001; daily use: PD + 40.3 %, p < .001). However, the perceived harmfulness perception of daily cannabis use declined (PD −5.6, p < .001). During that same time, lifetime, monthly, and daily use of tobacco, alcohol, and cannabis significantly declined (e.g., prevalence difference in monthly use; tobacco −55.0 %; alcohol −61.5 %; cannabis −44.3 %). Differences in harmfulness perception trends were observed between adolescents who used the substance in the previous month and those who did not, with a generally more pronounced change in perceived harm among those with recent use.

Over two decades, harmfulness perception of tobacco and alcohol increased, while cannabis perceptions remained stable or decreased. Changing perceptions, particularly the decline in perceived harmfulness of daily cannabis use, should be monitored to prevent potential future increases in use.