Due to the information asymmetry between patients and physicians, prescribing decisions are made by physicians. To promote their drugs, pharmaceutical companies spend considerable amounts to physicians, either by funding their attendance to conferences, or through donations and gifts. The relationships between healthcare professionals and the pharmaceutical industry, and the influence of promotion on doctors' prescribing behavior, is therefore a major issue for the regulation of healthcare spending and the sustainability of our healthcare system. Indeed, laboratory promotion can be beneficial if it provides information to physicians, which then leads them to prescribe treatments associated with better health outcomes. But it can be costly and inefficient if these prescriptions only result from the moral contract which binds doctors to firms and leads them to prescribe treatments which are less effective and / or more costly. This project aims to analyze the role of the relationships between the pharmaceutical industry and doctors on the prescription behavior of the latter. We mobilize a wide range of microeconomic analysis tools (microeconomic theory, mobilization of large administrative databases, laboratory testing and experimentation) in order to assess the impact of drug promotion on doctors' prescribing behaviors. in France. The project will answer to two important questions. First, we will analyze if physicians prescribe more drugs produced by pharmaceutical companies with which they have financial relations. We will also test whether this leads them to more expensive and/or less effective prescriptions than they would do without any financial relations. To answer these questions, we will use administrative, longitudinal and exhaustive data on physicians in France. More precisely, we will merge data from the “Transparence Santé” database to those of the national health insurance. Then, a testing with doctors will be implemented; this is the only possible way to analyze if these financial relations lead to less efficient prescriptions. In our second research question, we will analyze whether prescriptions result from better drug knowledge due to information provided by the pharmaceutical industry, or if they are motivated by financial incentives instead. We will develop a theoretical model whose predictions will be tested thanks to a lab experiment. This entire project will be carried out with a team with varied and complementary skills in microeconomics, as well as with public health doctors and a psychologist.