Table 1 Data collection to take place at the baseline visit

Demographics

Basic demographic information (date of birth, gender, ethnic group, educational qualification, occupational classification),

Additional baseline measures to allow future assessment of predictive ability of variables on weight change from baseline to follow-up:, heaviest weight to date, weight gain. For more information on investigation of weight gain see Additional file 2.

Medical history

Medical problems and concomitant medication.

Healthcare usage data

Baseline healthcare use (including primary care and secondary care visits) for economic analysis.

Mediators

Baseline measures to allow future assessment of change in potential mediators of the preloading effect, such as dependence, nausea from smoking, reward from smoking, urges to smoke, smoking stereotypy, confidence in quitting, motivation to quit.

Past smoking and quitting history

Information on smoking history (cigarettes per day, age at commencement, dependence, longest period of previous abstinence), and exhaled CO.

Additional baseline measures to allow future assessment of predictive ability of variables on weight change from baseline to follow-up: cigarettes per day, alcohol intake, previous quit attempt.

Previous use of pharmacotherapy for cessation and experiences of doing so, to assess suitability for treatment, and to examine whether it moderates the effectiveness of preloading.

Biological samples and measurements

Blood sample to identify genetic information (this will only take place at research centers with the resources to do so, where researchers are trained in phlebotomy, and will be optional for participants). For more information on genetic investigation see Additional file 1.

Weight, height Participant weight recorded using self-report and weighing scales. As people who relapse will not attend clinic at 6 and 12 month follow-ups the difference between self-reported and measured weights will be applied as a corrective adjustment to self-reported weight at follow-up in these participants. For more information on investigation of weight gain see Additional file 1.

Salivary sample to measure cotinine concentration (the best measure of smoking intensity).