Dual use of smokeless tobacco and cigarettes is an important contributor to the health effect associated with increased promotion of smokeless tobacco, particularly since tobacco companies are now aggressively promoting snus and other smokeless products as a way to deal with smoking restrictions rather than quitting.
An Australian study concluding that snus is likely to produce a net health benefit to population health, if adopted in sufficient numbers by inveterate smokers, did not account for dual use.36
They concluded that at least 19 people (averaging men and women) would have to begin using snus for each person that would otherwise have stopped all tobacco use to crossover from reducing health effects to producing net harm. Reducing the base probability of smokeless initiators becoming cigarette smokers or dual users to 0 and placing these people in the continuing smokeless group in our model (to reflect the Australian assumption of no dual use) produces a similar result, with the ‘crossover point’ at 21.5 new snus users per cigarette user avoided; well within the uncertainty of both models. (Increasing the tobacco-related health effect of smokeless in our model slightly, from 11 to 12 units, would make the estimated crossover points the same in the Australian model and our model.) The fact that our model can be modified to produce predictions similar to the Australian model increases confidence in our model and highlights the importance of dual use in determining the population-level health impact of smokeless tobacco promotion.
The prevalence of dual tobacco use has been found to be high among smokeless tobacco users in some,6,7,12,37
but not all,38
US studies. Because the health effects of cigarettes and smokeless are different, the health effects of concurrent (dual) use of these two tobacco products may be additive or even synergistic, may increase the risk of tobacco-related diseases and mortality above single product use.20
As noted above, the INTERHEART study found that dual use was associated with the highest increase in risk of acute myocardial infarction when compared to smoking and chewing tobacco alone.23
Since we assumed that dual use had, on average, a lower health effect than smoking cigarettes alone (assuming lower levels of carcinogen exposure were associated with dual use) and, in any event, no higher risks than smoking, we are almost certainly underestimating the health effect associated with increased promotion of snus.
The importance of dual use in predicting the population-level health effects of aggressive smokeless tobacco use is also reflected in the lower tobacco-related health effects in our second set of scenarios, based on older data on smokeless use patterns that assume low levels of dual use ( and ).
Dual use in a smokefree environment was modelled in all three alternative scenarios as having the effect of cutting quitting in half, with half the smokers adopting smokeless and three-quarters of them subsequently becoming dual users, based on the fact that the tobacco industry is explicitly promoting dual use of snus as a way to cope with smokefree environments () while continuing to smoke at other times. This increase in dual use is one of the most important reasons that promotion of snus is unlikely to have any substantial benefits on a population level, despite the fact that switching from cigarettes to snus reduces individual risk.
Sweden is widely cited as the prototype for promotion of smokeless snus as a harm reduction strategy even though the effects of snus use on smoking behaviour in Sweden remains controversial.39
The low rates of dual use reported for Sweden40
are based on a definition that requires someone to smoke cigarettes and use snus every day to be categorised as a dual user. This definition is not relevant to the way that snus is being promoted in the US, particularly as a way to cope with smokefree environments (), which might only encourage snus use on weekdays at work or in certain situations such as travel or attending concerts. Smokeless tobacco use is not associated with cigarette cessation in the US.38
More important, there are important differences in the way that snus is marketed in Sweden versus the US and other new markets that the multinational cigarette companies are developing. RJ Reynolds and Philip Morris are actively promoting Camel and Marlboro snus as line extensions of their cigarette brands.