Background. In 2017, 2.3 million patients were using Levothyrox (R) from Merck when the formulation changed. This new formulation generated more than 17,300 reports of adverse reaction. The crisis first emerged on social media and then grew in the media before health authorities took care of it Aims. To describe and analyse patients' experiences about the information of this subject during the crisis and then to understand their principles sources of knowledge. Methods. Interpretative phenomenological analysis, with semi-structured individual interviews of patients recruited in general practice. Maximum variation sampling was carried out, until data saturation was reached. Analysis assisted with NVivo 12 (R) software and triangulation by two researchers. Results. 15 patients were interviewed. During the crisis, patients felt a lack of information from their usual sources, which resulted in an adaptation of their behavior: active search for information with multiplication of sources and contents. The experiences were different according to the sources of information. Overexposure to information increased the feeling of misinformation and fear of a misunderstood phenomenon. Several protective factors appeared in a spontaneous or adaptive way: early information by a trusted health professional, refusing to be informed during crisis, feeling not concerned, behavior adaptation to protect oneself. Conclusion. Patients are becoming more informed, which does not mean that they are better informed. During a crisis, the phenomenon reaches its paroxysm with a loss of reference. The doctor's role as a source of health information then becomes crucial.< Réduire