Footnotes

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• Contributors All authors took an active role in the manuscript. CCO, SPM and ET conceptualised and designed the study. CCO collected the data. CCO, SPM and AM analysed and interpreted the data. CCO drafted the initial manuscript. All authors revised the manuscript for important intellectual content. ET obtained funding for this study and is responsible for the overall content. All authors approved the final manuscript.

• Funding This research is supported by the National Institute on Drug Abuse of the National Institutes of Health and FDA Center for Tobacco Products (CTP) under award number R01DA048529.

• Disclaimer The content of this research is solely the responsibility of the authors and does not necessarily reflect the views of the National Institutes of Health or FDA.

• Competing interests None declared.

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