Cigarette pack size and consumption: an adaptive randomised controlled trial

Ilse Lee, Anna K.M. Blackwell, Michelle Scollo, Katie De-loyde, Richard W. Morris, Mark A. Pilling, Gareth J. Hollands, Melanie Wakefield, Marcus R. Munafò, Theresa M. Marteau

Research output: Contribution to journalArticlepeer-review

3 Citations (SciVal)


Background: Observational evidence suggests that cigarette pack size – the number of cigarettes in a single pack – is associated with consumption but experimental evidence of a causal relationship is lacking. The tobacco industry is introducing increasingly large packs, in the absence of maximum cigarette pack size regulation. In Australia, the minimum pack size is 20 but packs of up to 50 cigarettes are available. We aimed to estimate the impact on smoking of reducing cigarette pack sizes from ≥25 to 20 cigarettes per pack. Method: A two-stage adaptive parallel group RCT in which Australian smokers who usually purchase packs containing ≥25 cigarettes were randomised to use only packs containing either 20 (intervention) or their usual packs (control) for four weeks. The primary outcome, the average number of cigarettes smoked per day, was measured through collecting all finished cigarette packs, labelled with the number of cigarettes participants smoked. An interim sample size re-estimation was used to evaluate the possibility of detecting a meaningful difference in the primary outcome. Results: The interim analysis, conducted when 124 participants had been randomised, suggested 1122 additional participants needed to be randomised for sufficient power to detect a meaningful effect. This exceeded pre-specified criteria for feasible recruitment, and data collection was terminated accordingly. Analysis of complete data (n = 79) indicated that the mean cigarettes smoked per day was 15.9 (SD = 8.5) in the intervention arm and 16.8 (SD = 6.7) among controls (difference − 0.9: 95%CI = − 4.3, 2.6). Conclusion: It remains unclear whether reducing cigarette pack sizes from ≥25 to 20 cigarettes reduces cigarette consumption. Importantly, the results of this study provide no evidence that capping cigarette pack sizes would be ineffective at reducing smoking. The limitations identified in this study can inform a more efficient RCT, which is urgently required to address the dearth of experimental evidence on the impact of large cigarette pack sizes on smoking. Trial registration:

Original languageEnglish
Article number1420
JournalBMC Public Health
Issue number1
Early online date18 Jul 2021
Publication statusPublished - 31 Dec 2021

Bibliographical note

Funding Information:
This research was funded in whole, or in part, by the Wellcome Trust [Grant number 206853/Z/17/Z]. For the purpose of open access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission.

Publisher Copyright:
© 2021, The Author(s).


  • Adaptive design
  • Cigarette packaging
  • Pack size
  • Tobacco control

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health


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