Introduction Tobacco smoking is one of the leading causes of preventable death. This is not inevitable as tobacco control tools have become more powerful and more effective. Among these, warnings on cigarette packs have proven to be somewhat effective. Our objective is to increase the efficacy of antismoking warnings by using innovative psychological approaches and to create an experimental setting for the evaluation of these new warnings based on behavioural indicators.

Methods and analysis First, we created new warnings based on three categories of motivational leverage and on harm reduction. New warnings with innovative texts and pictures were designed for each category and inserted on plain packs. We will then use standard indicators to compare their effect to that of control packs: plain pack without warning, plain pack with conventional warning and branded pack with conventional warning. Second, the novelty of our approach will consist in designing an experimental protocol that uses monetary incentives to evaluate the effect of warnings. Subjects will be able to ‘sacrifice’ part of their participation defrayal to purchase a good whose subjective value is related to one’s attitude towards smoking. These monetarily incentivised measures are designed to assess smokers’ immediate/mid-term intention to quit and non-smokers’ aversion to smoking. In both cases, the monetary amounts individuals accept to sacrifice may be a more reliable measure than declarative responses, which may be distorted by several hypothetical biases. In the end, we should be able to robustly measure the impact of our new warnings between intervention and control groups by using both traditional indicators and our new monetarily incentivised measure.

Ethics and dissemination The ethics committee of the Groupement des Hôpitaux de l’Institut Catholique de Lille approved the research protocol on 5 July 2019 (CIER 2019-22). Results will be presented at scientific meetings and published.