App content validity and usability was tested in a previous study at the pain unit of the Vall d'Hebron Hospital (Suso-Ribera et al., in preparation). Thus, the study objective is to test if the introduction of this tool in the day-to-day work of the pain unit improves pain management of chronic pain patients. To do this, it is necessary to compare the evolution of patients who follow the usual treatment at the pain unit (without app) with a group of patients who do use the Pain Monitor app. In addition, the present study investigators have created a new utility that allows alarms to be generated by healthcare professionals in the presence of an undesired event, such as an adverse effect of the medication or a lack of response to medical treatment. Before determining that both the use of the app and this new utility (alarms) are beneficial for patient care, it is necessary to perform a clinical trial comparing the 3 conditions mentioned above: