BACKGROUND-AIM:
In Poland, the popularity of novel nicotine products, such as e-cigarettes, has increased among youth in recent years. However, their use is also combined with concurrent use smoking of tobacco cigarettes as part of the dual use phenomenon. Examining the level of dependence between the two types of products is also important, since nicotine delivery differs by product type, concentration, and user behaviour. The aim of this study is to determine the level of nicotine dependence in exclusive tobacco cigarette users, exclusive e-cigarette users, and dual users among Polish adolescents, by comparing the values of the Heaviness of Smoking Index (HSI) and Heaviness of Vaping Index (HVI).

METHODS:
The study was conducted in 2020, and it was representative for the overall Polish youth population, with a sample of 16712 secondary school students (aged 15-18) from 200 schools. Participants were recruited through a stratified and random sampling method. Data collection was conducted via Computer-Assisted Web Interviews (CAWI), using a questionnaire based on the Global Youth Tobacco Survey (GYTS) framework. To address the differing score ranges of the HSI (0–6) and HVI (0–10), values were rescaled (HSI×10, HVI×6) to enable meaningful comparisons between the indices.

RESULTS:
As many as 18.3% of participants (N=3064) were dual users, while users of exclusive one type of product made up only 2.9% (N=485) of study sample. The majority of dual users attended technical schools (58.8%), with heavy dual users being predominantly male (62.8%). The most common subtype of dual user was light dual user (6.3%, N=1053), while 2.5% (N=418) were heavy dual users. Heavy dual users had a median HSI of 10 (range of answers 0-60) and HVI of 30 (range of answers 0-42). Daily users who exclusively used e-cigarettes (1.8%) had a median HVI score of 24 (range of answers 0-42), whereas daily users who exclusively used tobacco cigarettes (1.1%) had a median HSI score of 10 (range of answers 0-60).

CONCLUSIONS:
Dual use of tobacco and e-cigarettes is multiple times more popular among Polish adolescent than using only an e-cigarette or tobacco cigarette. Daily concurrent use of both electronic and tobacco cigarettes is associated with a higher level of dependence on both products compared to those who use only one type of product daily. As dual use imposes greater health risks and poses a significant public health concern, tailored prevention strategies are essential and should be implemented during early adolescence.