Materials
’
The NVP: The ‘Aspire PockeX’ or the ‘Juul’ were randomly assigned to each participant (20 participants have been randomised to Juul and 25 to Aspire PockeX; unequal numbers were due to a delay in obtaining Juul). The ‘‘Aspire PockeX’ is an all-in-one second-generation NVP kit with a 1500mAh internal battery and integrated 2 ml e-liquid tank. Participants could choose an e-liquid with 18 mg/ml concentration of nicotine, with tobacco, fruit or menthol flavour. The Juul is a slim NVP that has no buttons or switches and uses a regulated temperature control. It is charged through USB ports and has prefilled cartridges (‘pods’) of 18 mg/ml nicotine concentration in UK and participants could choose tobacco, mint, mango or menthol flavour. These NVPs were selected on the basis of nicotine delivery efficiency (Juul) and popularity (Aspire PockeX) in UK when the study begunThe HTP: ‘IQOS’ is an HTP manufactured by Philip Morris, which heats specially designed tobacco sticks called HEETS. IQOS was the most popular HTP in the UK when the study begun. HTPs were fully charged prior to the session and participants could choose tobacco smooth, rich tobacco, or menthol HEETS of 18 mg/g nicotine to use. The amount of nicotine per gram of tobacco in a regular IQOS tobacco stick is ~ 15.4 mg/g and in a menthol tobacco stick is ~ 16.4 mg/g