In the study published in the March 2011 issue of Addiction[1], Ferguson et al. present data on secondary analyses of a randomized trial in which 608 participants were allocated to one of three intervention groups (placebo, 2 mg nicotine gum and 4 mg nicotine gum) [2]. The authors conclude that participants who quit smoking and used nicotine gums in the first 30 days experienced less weight gain than smokers who used placebo gums. In a previous report on the same study, the authors did not find a statistically significant association between allocation group and weight gain [2]; therefore, we wonder whether the exclusion of 59 (9.7%) of participants after randomization in the present analyses might have influenced the results.

In the present paper, the authors analysed data from 103 participants from the original 608 participants. They excluded 445 participants (73.2%) because they failed to achieve continuous abstinence at 30 days, and 59 participants (9.7%) because they had been assigned to an off-label active treatment dose according to the US Food and Drug Administration labelling instructions [if <25 cigarettes per day (CPD): 2-mg nicotine gums; if >25 CPD: 4-mg nicotine gums]. This last exclusion criterion implies that no participants were excluded from the placebo group, and given the mean cigarette consumption of 22.2 CPD overall [1], more participants might have been excluded from the 4-mg group than the 2-mg group (i.e. there were more participants allocated in the 4-mg group excluded because they smoked fewer than 25 CPD and fewer participants excluded from the 2-mg group because they smoked more than 25 CPD). The present paper does not mention how many participants were excluded in each allocation group, but based on the original paper [2] we calculated that 17 participants might have been excluded in the 2-mg group and 42 in the 4-mg group (see Appendix Table below for details of the calculation, not to be published).

Selective exclusion of participants from the analyses after randomization might have influenced the results [3]. Before educating smokers on the benefits of nicotine gums over weight gain on the basis of the present results, we would find it helpful to present the full flowchart of included and excluded participants from the baseline sample for each allocation group, and also to present additional analyses without excluding the 59 participants who were assigned to an off-label active treatment dose [1].


  1. Top of page
  2. Declarations of interest
  3. References
  • 1
    Ferguson S. G., Shiffman S., Rohay J. M., Gitchell J. G., Garvey A. J. Effect of compliance with nicotine gum dosing on weight gained during a quit attempt. Addiction 2011; 106: 6516.
  • 2
    Garvey A. J., Kinnunen T., Nordstrom B. L., Utman C. H., Doherty K., Rosner B. et al. Effects of nicotine gum dose by level of nicotine dependence. Nicotine Tob Res 2000; 2: 5363.
  • 3
    Hulley S. B., Cummings S. R., Browner W. S., Grady D., Newman T. B. Designing Clinical Research, 3rd edn. Philadelphia, PA: Lippincott Williams & Wilkins; 2007.