Footnotes

• Contributors PTH wrote the original draft. TE provided feedback and suggestions. Both authors reviewed and approved the final manuscript.

• Funding PTH effort is supported by the National Cancer Institute of the National Institutes of Health under award number R03CA195124 and the Center for Tobacco Products of the US Food and Drug Administration. TE effort is supported by the National Institute on Drug Abuse of the National Institutes of Health under award number P50DA036105 and the Center for Tobacco Products of the Food and Drug Administration. The content is solely the responsibility of the authors and does not necessarily represent the views of the NIH or the FDA.

• Competing interests PTH does not have any competing interests to declare. TE is a paid consultant in litigation against the tobacco industry and is named on a patent application for a device that measures the puffing behaviour of electronic cigarette users.

• Provenance and peer review Not commissioned; externally peer reviewed.