Does e-cigarette experimentation increase the transition to daily smoking among young ever-smokers in France?

According to multiple studies, e-cigarette use among adolescents is associated with subsequent smoking initiation. However, little is known about its effect on the transition from smoking initiation to daily smoking.Using retrospective data from a French national representative survey collected in 2017 (n = 39,115), we analyzed the role of ever using e-cigarettes on daily cigarette smoking status at 17 among ever smokers (n = 21,401). Risk-ratios (RR) were computed through modified Poisson regressions with an inverse probability of treatment weighting (IPTW) approach.Among French adolescents aged 17, 16.8 % declared current e-cigarette use (1.9 % reported daily use) and 34.1 % cigarette smoking (25.1 % reported daily smoking). Among ever-smokers, adolescents who declared having ever used e-cigarettes were less likely than those who did not to transition to daily smoking at 17: RR = 0.62 95 %CI [0.60 - 0.64]. We found similar results for those who experimented with e-cigarettes before initiating smoking, RR = 0.76 95 %CI [0.66 - 0.89].Our results found no evidence of an increased risk of transitioning to daily smoking at 17 among ever-smokers who also experimented with e-cigarettes. Further studies should investigate the longer-term role of vaping on future smoking habits with the use of causal inference methods.