Most smokeless tobacco use is not a causal gateway to cigarettes: using order of product use to evaluate causation in a national US sample

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Abstract
Aims To evaluate non‐causal and causal patterns of smokeless tobacco (SLT) and cigarette use; to assess the prevalence of ‘non‐gateway’ and possible ‘gateway’ patterns of SLT use.Design and setting Data from the Cancer Control Supplement to the 1987 National Health Interview Survey, a representative survey of non‐institutionalized adults in the United States. From reported age at first use, participants were categorized by type and sequence of tobacco product use. SUDAAN 8.0.1 was used for statistical analyses.Participants Males aged 18–34 (n = 3454), weighted to provide estimates of the US population. A subsample of males aged 23–34 (n = 2614) was analyzed to minimize the possibility of future product switching.Measurements Smoking status, smokeless tobacco (snuff, chewing tobacco, both) use status, age at regular use of cigarettes, age at first use of smokeless tobacco.Findings Of those 23–34‐year‐olds who had ever used SLT with or without cigarettes, 77.2% (95% CI: 71.3, 83.3) were classifiable as non‐gateway users in that 35.0% (95% CI: 29.9, 40.1) had only used SLT and 42.2% (95% CI: 36.8, 47.7) had used cigarettes first. Cigarette use in younger cohorts was less common, despite increased SLT use. Those who used cigarettes before moist snuff were 2.1 times more likely to have quit smoking (95% CI 1.21,6.39) than cigarette‐only users.Conclusions The large majority of SLT users are non‐gateway users. Causal gateway effects should be of minor concern for policy. SLT may be more likely to prevent smoking than cause it.