Non-adherence, defined as the discrepancy between patients' behaviour and medical prescriptions, is a massive public health issue, the consequences of which are serious. Nearly half of the patients who have a chronic disease do not take their treatment as prescribed. In order to improve our understanding of this phenomenon and to remedy it, the proposed research will examine following hypothesis : in the case of long-term conditions for which a treatment is effective and has little side effects, a cause of intentional non-adherence could be that (1) the patients perceive or, in a way, create, different types of uncertainty regarding the causal relationship between their treatment and their health and that (2) they consider that this uncertainty makes the case for non-adherence. This assumption is based on patients' adherence behaviour that I evidenced in previous research on cystic fibrosis and Wilson's disease. The proposed research will consider 4 disorders and 5 treatments that are : chronic myeloid leukemia treated with imatinib, Parkinson's disease treated with dopamine agonists and by L-DOPA, diabetes 2 treated with metformin and hypertension treated with antihypertensive treatments. The inquiry will proceed in three steps, that aim at (1) understanding the phenomenon through a qualitative study (focus groups and interviews), (2) designing an intervention based on this understanding, through an interventional study, in order to reduce the phenomenon and (3) at validating empirically the effectiveness of the intervention, through a quantitative study. The proposed research matches the first goal of the Horizon 2020 programme for a Better Society. It is at the intersection of 3 academic disciplines: (1) sociology of health, (2)  psychology of risk perception and behaviour change and (3) medicine, i.e. chronic disease management. And it is to be performed in a Franco-Dutch cooperation between Université Lille 2 and Technical University Eindhoven.