Rodu is correct in stating that because the U.S. population is so large, even a small percentage of cigarette smokers switching to smokeless would mean many thousands of people [1]. However, he has done only half the math- the other half is that exclusive smokeless users also switch to cigarettes. In fact, it is easy to see from Table 2 in Zhu et al. that the number switching from smokeless to cigarettes is much greater than the number of smokers switching to smokeless [2]. The reason is that the rate of switching from smokeless to cigarettes is more than 10 times higher than the rate of switching from cigarettes to smokeless. One can use the CPS 2002-2003 longitudinal sample with the proper population weights and find that 120,266 people switched from smokeless to cigarettes, whereas only 53,850 switched from cigarettes to smokeless. Someone else could use these numbers to suggest that if more people use smokeless, more will use cigarettes (although that is not the interpretation in Zhu et al.). That is why it is important not to selectively choose numbers from Zhu et al. and ignore the larger context [3].

Bergen and Phillips dismiss our empirical results as “not interesting or useful to know” [4], and then they reiterate the well known arguments for harm reduction. It is true that our results do not support Bergen and Phillips’ position. Our paper strives to address pertinent arguments from both sides of the harm reduction debate. After examining possible explanations (socio-cultural, price, and product differences) for the difference between the Swedish results and those that we found in the U.S., we raise a cautionary note in our conclusion. Readers can judge for themselves whether our paper is an anti-harm reduction opinion piece or a careful empirical analysis. Interested readers with no access to the PDF file for our paper can request a copy by sending an email to szhu@ucsd.edu.

Conflict of Interest: None to declare

1. Rodu B. Evidence from Zhu et al. that American smokers have switched to smokeless tobacco. Tob Control eLetter published online February 20, 2009. http://tobaccocontrol.bmj.com/cgi/eletters/tc.2008.028209v1#2853

2. Zhu S-H, Wang JB, Hartman A, Zhuang Y, Gamst A, Gibson T, et al. Quitting cigarettes completely or switching to smokeless: Do U.S. data replicate the Swedish results? Tob Control. Published Online First: 23 January 2009. doi:10.1136/tc.2008.028209

3. Zhu, S-H. Gamst, A. Response to Nitzkin and Rodu. Tob Control eLetter published online February 11, 2009. http://tobaccocontrol.bmj.com/cgi/eletters/tc.2008.028209v1#2837

4. Bergen P, Phillips CV. Response to Zhu et al. Tob Control eLetter published online February 20, 2009. http://tobaccocontrol.bmj.com/cgi/eletters/tc.2008.028209v1#2862

The authors of this paper (1), the responders (3), and most everyone else agree that smoking is high risk, and that the use of smokeless tobacco is fairly low risk. In any other area, the obvious conclusion would be to encourage smokers to switch to the lower risk alternative.

However, what follows instead is a strange and yet quite common argument that because many smokers might not switch, this alternative should not be promoted. Whether or not most people will actually use a low-risk alternative has never been a necessary precondition for promoting or introducing it. Effectively, the authors suggest that because tobacco harm reduction currently only saves the lives of a few thousand American smokers per year, it should not be encouraged.

But this study actually tells us nothing about how many more might be saved. Zhu et al. argue that their paper adds needed empirical data to the discussion, but in fact they have merely measured something that is not interesting or useful to know, and have confirmed something that no one would ever doubt: They discovered that when a population of smokers does not know that there is a low-risk alternative, then it is likely that few of them will switch to it. Presumably no one would fail to predict that, and reporting it says nothing about the potential benefits of promoting harm reduction.

The authors acknowledge that smokers are unaware of the comparative risks of tobacco use, and to their credit, point out that this shortfall is something that the public health community must still address. However, the authors mislead somewhat by stating that a reason that switching may not have occurred at higher rates might be due to the fact that despite its general availability, smokeless tobacco has not been promoted as a safer alternative, when it is more the case that smokeless tobacco has been actively discouraged as an alternative for smokers. Yes, smokers can buy smokeless tobacco instead, but they do not know there is good reason to do so. The lack of knowledge is the result of a concerted (and successful) disinformation campaign by anti-tobacco extremists to convince people that there are no low-risk nicotine products. Whatever the present paper's empirical findings about historical switching rates, such findings tell us almost nothing about how many smokers would switch if they knew the truth.

If someone was interested in producing actual useful empirical information, rather than just contributing to anti-harm-reduction rhetoric, the most useful experiment would be to education a population about the comparative risk and then observe how many smokers make the switch. If few switched, then the authors' claims would actually be supported. (Though their policy conclusions would still not be supported: It would still be ethically mandated, as well as beneficial to some extent, to tell smokers the truth about alternatives and encourage them to switch, even if most of them chose not to do so.)

Perhaps the only interesting question that arises from this analysis is why Swedish smokers switched to smokeless tobacco. Though a much larger portion of Swedes know the truth than do Americans, many still incorrectly think the risks from snus are similar to those from smoking. Part of the explanation for the popularity of smokeless tobacco is certainly cultural (or, put another way, an historical accident, an economic "path dependence" resulting from social phenomena that trace back about four decades). But part of the explanation is that, despite the widespread lack of knowledge, Swedes are not being actively bombarded by so much disinformation that it drowns out the truth. An American who tries to learn the truth must learn to ignore the disinformation coming from the U.S. national government, other government entities, and most major self-styled health organizations, including some that are respectable sources of advice in other areas (4), and sort through to the rare accurate information that is available (e.g., 5, 6,7). (Nitzkin and Rodu address this point well (2)). Moreover, an American who learns the truth in spite of the disinformation and then wants to tell others needs to then convince the others that most of the authorities they normally trust are lying, making it quite difficult to spread the truth once it is learned.

Despite being largely an historical accident, the Swedish experience with tobacco harm reduction is still a great public health triumph. Zhu et al. admit that tobacco harm reduction seems effective in Sweden but are loathe to generalize or to suggest that we should even try to pursue such triumph elsewhere. Extending their reasoning, consider this: In 1984, in the United States roughly 14% of individuals used seatbelts (8), which is less than half the prevalence in Sweden more than a decade earlier (9). The general knowledge about the usefulness of seatbelts was similar in the two countries, so there was clearly some cultural difference that resulted in Americans adopting the restraints at a lower rate. Following Zhu et al.'s logic, we should have just conceded that Americans are culturally uninterested in using seatbelts, and that the Swedish success could not be generalized.

Fortunately for the tens of thousands of Americans who have been saved by seatbelts over the last few decades, in public health (in contrast to anti-tobacco activism), we generally see success at reducing harm as something to pursue and emulate rather than to dismiss as too foreign to work.

Conflict of Interest

The authors' research is partially supported by an unrestricted (completely hands-off) grant to the University of Alberta from U.S. Smokeless Tobacco Company. Dr. Phillips has consulted for U.S. Smokeless Tobacco Company in the context of product liability litigation. Dr. Phillips is also a member of British American Tobacco's External Science Panel that deals with developing reduced harm products.

References

1. Zhu S-H, Wang JB, Hartman A, Zhuang Y, Gamst A, Gibson JT et al. Quitting cigarettes completely or switching to smokeless: do U.S. data replicate the Swedish results? Tob Control; in press.

2. Zhu et al. Response to Nitzkin & Rodu's comments. Tob Contol eLetter published online February 11, 2009.

3. Nitzkin JL, Rodu B. Promoting snus will save lives in the USA. Tob Control eLetter published online February 6, 2009.

4. Phillips C, Wang C & Guenzel B. You might as well smoke: the misleading and harmful public message about smokeless tobacco. 2005. BMC Public Health 5:31.

5. Phillips C. Tobaccoharmreduction.org. (At: http://www.tobaccoharmreduction.org)

6. Rodu B & Godshall WT. 2006. Tobacco harm reduction: an alternative cessation strategy for inveterate smokers. Harm Reduction Journal 3:37.

7. Royal College of Physicians. 2007. Harm reduction in nicotine addiction: Helping people who can't quit. (Available at: http://www.rcplondon.ac.uk/pubs/brochure.aspx?e=234)

8. Presidential Initiative for Increasing Seat Belt Use Nationwide: Recommendations from the Secretary of Transportation. April 16, 1997. http://www.nhtsa.dot.gov/people/injury/airbags/Archive- 04/PresBelt/fullreport.html

9. Phaner G & Hane M. 1979. Seat Belts: Opinion Effects of Law Induced Use. Journal of Applied Psychology 64(2):205-212.

Nitzkin and Rodu raise several interesting points about harm reduction and how they would like to see the current FDA bill (HR1108/S625) be improved [1]. However, the purpose of Zhu et al.’s paper is not to advocate for or against harm reduction. It is simply to examine whether current US data replicate the Swedish results [2].

If large numbers of US smokers could be induced to switch to smokeless tobacco, that would certainly help to increase the population smoking cessation rate. However, our study shows that very little switching has occurred in the US population, unlike the Swedish population. Smokeless tobacco has been promoted in both countries for a long time, without a focus on relative risk. In light of these findings, we sound a cautionary note. Tobacco control policymakers face difficult choices, and our hope is that these new results might be helpful.

Nitzkin and Rodu’s arguments for the merits of harm reduction are well known because there has been so much debate on this topic. Some are convinced of such arguments while others are not [3,4]. Our paper aims to inject empirical data into what sometime seems like an endless logical exercise without new information. The debate is often filled with hypothetical scenarios on how things might work this or that way. Some of these hypotheses may turn out to be correct. Our paper does not say that the hypotheses for harm reduction are wrong. It simply says that new results from the US are quite different from the Swedish results and do not support the idea that promoting smokeless tobacco necessarily leads to increased smoking cessation on a population level. We believe that the field needs more such empirical research.

That research can be misused, however, as in Nitzkin and Rodu’s extrapolation of our finding that US men quit smokeless tobacco products at three times the rate of quitting cigarettes. They suggest that this means that “encouraging American smokers to switch to smokeless products will increase the number that eventually quit all use of tobacco and nicotine.” They ignore our larger finding that US smokers are not switching to smokeless in the first place, and they fail to understand that the differential quit rates suggest that, mathematically speaking, US men tend to quit smokeless before quitting cigarettes. Are Nitzkin and Rodu necessarily wrong, then, in suggesting such a hopeful scenario? We would not say that. One can easily imagine various scenarios in which smokeless tobacco helps smokers quit cigarettes or even all forms of tobacco. But however enticing those scenarios may be, the US data do not yet support them.

1. Nitzkin JL, Rodu B. Promoting snus will save lives in the USA. Tob Control eLetter published online February 6, 2009.

2. Zhu S-H, Wang JB, Hartman A, Zhuang Y, Gamst A, Gibson JT et al. Quitting cigarettes completely or switching to smokeless: do U.S. data replicate the Swedish results? Tob Control; in press.

3. Rodu B, Godshal WT. Tobacco harm reduction: an alternative cessation strategy for inveterate smokers. Harm Reduction J 2006;3:37. Open access, available at: http://www.harmreductionjournal.com/content/3/1/37 (Accessed February 10, 2009).

4. Tomar SL, Fox BJ, Severson HH. Is smokeless tobacco use an appropriate public health strategy for reducing societal harm from cigarette smoking? Int J Environ Res. Pub Health 2009, 6(1), 10-24; doi:10.3390/ijerph6010010

A recent article in Tobacco Control 1 reported that 33% of cigarettes are consumed by smokers who had a current mental disorder. The title, abstract and discussion of that article stated that this 33% represented how much “mental disorders contribute to tobacco consumption in New Zealand.” This statement is misleading for at least two reasons. First, although 33% of smokers had a current mental disorder, 21% of nonsmokers also had a current mental disorder; thus, the actual excess that mental disorders could “contribute” is +12%, not 33%. Second, and more importantly, neither this study nor the prior literature has consistently shown that mental disorders per se cause the initiation of smoking, cause smokers to smoke more or interfere with cessation 2. For example, recent reviews have concluded that prior alcohol dependence and depression do not appear to impair smoking cessation 3,4. Since we cannot randomize smokers to mental illness, we must rely on associative data. Among the criteria for judging whether an association is causal 5, the plausibility, replicability, strength of the association, dose-responsivity of the association, and the consistency with other knowledge argue for causality. However, data on whether smoking remits if mental disorders remit, whether the association persists when all reasonable confounds are considered, evidence of specificity, and temporal relationship do not strongly argue causality. For example, a) most mental disorders temporally follow, not precede, smoking, b) those in remission from a psychiatric disorder have not been shown to stop smoking and c) smoking is associated with over 20 different mental disorders suggesting nonspecificity 2. Finally, even if the association was causal, it is unlikely that mental illness accounts for 100% of the reason these smokers smoke. If it accounted for only half, then the excess due to mental disorders would be only +6% (half of +12%). In summary, the “contribution” of psychiatric co-morbidity to the current prevalence of smoking is likely much less than the stated 33%.

References

1. Tobias M, Templeton R, Collings S. How much do mental disorders contribute to New Zealand's tobacco epidemic? Tobacco Control 2008;17:347- 350.

2. Hughes JR. Comorbidity and smoking. Nicotine and Tobacco Research 1999;1:S149-152.

3. Hughes JR, Kalman D. Do smokers with alcohol problems have more difficulty quitting? Drug Alcohol Depend 2005;82:91-102.

4. Hitsman B, Borrelli B, McChargue DE, Spring B, Niaura R. History of depression and smoking cessation outcome: A meta-analysis. J Consult Clin Psychol 2003;71:657-663.

5. Hill AB. The environment and disease: Association or causation? 295-300. 1965.