Youth tobacco use remains a significant public health concern in the U.S. (Gentzke et al., 2020; Wang et al., 2019). In 2020, 23.6% of high school students (3.65 million) and 6.7% of middle school students (800,000) reported current (i.e., past 30 days) use of any tobacco product (Gentzke et al., 2020). In the same year, electronic cigarettes (e-cigarettes) were the most commonly used tobacco product (Gentzke et al., 2020). Of concern, rates of use of two or more tobacco products are relatively high; in the U.S., 34.7% of youths who report using a tobacco product report current use of multiple products (i.e., use of 2 or more tobacco products in the past 30 days) (Gentzke et al., 2020; Wang et al., 2019). Multiple product use is especially concerning because compared to single product use, youth multiple product use is associated with higher levels of nicotine dependence (Ali et al., 2016), lower likelihood of expressing quit intent (Ali et al., 2016), and a greater likelihood of using other drugs (Creamer et al., 2016). To prevent youth from multiple product use, researchers need to understand the factors contributing to multiple product use.

The first nicotine product tried may be especially relevant to multiple nicotine product use in several ways.

First, youth who have a common liability to use multiple products may be uniquely attracted to the product (Van Leeuwen et al., 2011). In this case, genetic and individual factors influence the choice of the first substance used. Second, there may be unique characteristics of a product that drive multiple product use (Kandel et al., 2006). For example, it may not be appropriate to chew and spit out some types of smokeless tobacco indoors, therefore, smokeless tobacco users may supplement their use with e-cigarettes. Third, there may be an interaction between individual and product-specific characteristics, whereby individual factors and the first product tried work together to contribute to multiple product use.

Although there continues to be debate regarding the theoretical rationale for why the first product tried may be associated with subsequent product use, empirical evidence supports the conceptual relevance of the first nicotine product tried for understanding the use of other nicotine products. Regional studies have examined the associations between the first nicotine product tried and multiple nicotine product use cross-sectionally (Kowitt et al., 2019; Meier et al., 2015; Sutfin et al., 2015). One study among college students showed that, first trying smokeless tobacco or cigarettes (rather than hookah or electronic tobacco products) was associated with greater likelihood of multiple product use (Meier et al., 2015), and another among college students showed that multiple product use was more common among those first tried with hookah and smokeless tobacco (Sutfin et al., 2015). One study showed that compared to high school students who first tried cigarettes, high school students who first tried e-cigarettes were less likely to be current multiple product users (Kowitt et al., 2019). In contrast, those who first tried cigars or smokeless tobacco (vs. cigarettes) were more likely to be multiple product users (Kowitt et al., 2019). While there have been cross-sectional examinations, to date, there have been no prospective studies examining how the first product tried relates to future multiple product use among youth. Moreover, despite the documented associations between multiple product use and nicotine dependence, no study has examined the association between the first product tried and nicotine dependence. The purpose of the current study is to describe the degree of risk for no use, single product use and multiple product use after first trying a novel nicotine product (e.g., e-cigarettes) relative to nicotine products that have been on the market longer. The current study extends the existing research by examining the prospective associations between the first product tried and subsequent multiple product use and nicotine dependence.

Given the multiple nicotine products available for consumption and the ever-changing tobacco product landscape, it is important to understand which specific tobacco products are first tried and their subsequent association with future use patterns (i.e., no use, single nicotine product use, multiple nicotine product use) and nicotine dependence (Gallaway et al., 2018). Whereas cigarettes were previously the most common first product tried (Kowitt et al., 2019; Ross et al., 2018), recent studies have shown that e-cigarettes are the most common first product tried among youth (Grobman et al., 2021). We used e-cigarettes as the referent for first product tried given evidence that e-cigarettes are the most commonly used product (Gentzke et al., 2020) and findings that e-cigarette use may serve as an entry point into nicotine product use for many youths and may facilitate experimentation and use of other nicotine products (Liu et al., 2016). Prior research has shown that those who start with e-cigarettes progress to cigarettes (Liu et al., 2016); however, the other patterns of progression to other combinations of products is not established.

This paper addresses gaps in our understanding of the first product tried, multiple product use and nicotine dependence by examining 1) demographic factors associated with first trying other products, 2) how the first product tried (vs. e-cigarette) is associated with future multiple product use and 3) how first product tried is associated with future symptoms of nicotine dependence. Although research has shown that e-cigarette use now leads cigarette use, prospective observations using nationally representative data to examine the influence of e-cigarettes as the first product tied has on future patterns of use are lacking. This information is especially important for clinicians and other public health workers who are tasked with preventing tobacco use behaviors among youth and communicating health risks associated with youths' pattern of use. Thus, the current study uses Waves 1 and 4 of the Population Assessment of Tobacco and Health (PATH) to examine the role of first product tried on future multiple product use and nicotine dependence among youth. Two waves of the PATH are required because in the youth population, we expected that most participants would have recently first tried a tobacco product at Wave 1 and thus, would not have had sufficient time to develop a stable pattern of use. Therefore, we assessed current use status and nicotine dependence at the most distant time point at which the outcomes were available in PATH at the time of analysis, Wave 4. By controlling for age of first product tried, we were able to address the question: if youth tried their first product at the same age, how would their first product tried impact their nicotine product use 3 years later?