ACKNOWLEGDEMENTS Authors would like to thank the nurses of ward 309 (Aberdeen Royal Infirmary) for consenting participants and NHS Grampian Biorepository staff. Also, Gary Cameron for performing the LC-MS/MS cotinine analyses and Ms Linda Robertson for technical assistance. The authors state there are no conflicts of interest. Author contributions: NW, PF and PAF designed the research; NW conducted research, analysed data and wrote paper; PAF responsible for ethics (SAFeR study). All authors read and approved the final manuscript. Authors would like to thank the study funders: Glasgow Children’s Hospital Charity YRSS/PHD/2016/05 and UK Medical Research Council: MR/L010011/1, to PAF & PJOS and MR/P011535/1 to PAF. The funders played no role in the conduct, analysis or publication of the studyPeer reviewedPublisher PD