Footnotes

• Twitter @gracekongphd, @DDavisPhD

• Contributors Study conception and design: GK, MEM. Interpretation of results: GK, MEM, DD, KB, SK-S. Draft manuscript preparation/edits: GK, MEM, DD, KB, SK-S. All authors reviewed the results and approved the final version of the manuscript.

• Funding This study is funded by Institute of Drug Abuse (NIDA) and the Food and Drug Administration’s Center for Tobacco Products (FDA CTP) grant U54DA036151 (SK-S). Support for authors is also provided by R01DA049878 (GK), K01DA065494 (DD) and R01DA054993 (KWB). The content of this paper is solely the responsibility of the authors and does not represent the official views of the NIH or the FDA.

• Competing interests None declare.

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

• Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.