BACKGROUND AND AIMS: It is postulated that due to decreased smoking rates and increased denormalisation of smoking, those who start and maintain smoking have more socially disadvantaged characteristics and are more dependent on nicotine than those who do not (the so-called 'hardening' hypothesis). The aim of this study was to measure changes in daily smoking and cigarette consumption among Finnish adolescents according to background factors.

DESIGN AND SETTING: A repeated cross-sectional study using data from European School Survey Project on Alcohol and other Drugs (ESPAD) on six representative cross-sections of 15- to 16-year-old students between 1999 and 2019 in Finland. A total of 11 377 males and 12 247 females.

MEASUREMENTS: The outcome measures included the proportion of daily smokers among current smokers, daily smoking and the estimated mean number of smoked cigarettes per day (CPD). Substance use, parental monitoring and school performance were used as independent variables. All measures were self-reported.

FINDINGS: Daily smoking decreased over time and daily smokers constituted a smaller part of current smokers in 2019 compared with 1999 (the ratio among boys 0.68 and 0.43, respectively; among girls 0.59 and 0.43). Boys using cannabis (interaction between cannabis*survey year: P = 0.020; in 2019 odds ratio [OR]: 3.68, 95% confidence interval [CI] 2.23-6.08) and girls with heavy episodic drinking (interaction between heavy episodic drinking*survey year: P = 0.006, in 2019 OR: 9.00, 95% CI 5.61-14.42) had elevated adjusted odds for daily smoking over time. The estimated mean number of CPD decreased among daily smokers from 9.0 in 1999 to 7.2 in 2019 (P = 0.0002) and the differences diminished between groups based on gender, snus/alcohol use and parental monitoring. The between-group differences remained with regard to cannabis use (P = 0.0233 in 2019) and school performance (P = 0.0111 in 2019).

CONCLUSIONS: Among currently smoking Finnish adolescents, the proportion of daily smokers decreased between 1999 and 2019, as did the number of cigarettes smoked per day (CPD) among daily smokers, suggesting an absence of 'hardening' in this group. However, differences were observed related to the odds of daily smoking and the mean number of CPD, indicating the change has been less favorable among some adolescent groups than others.