Bipolar disorders are severe and complex psychiatric disorders and lithium remains one of the most effective drugs for relapse prevention. Despite its effectiveness, prescription of lithium therapy can be complicated because of its narrow therapeutic range. Furthermore, adherence to treatment is generally low. One means of improving adherence would be to make the patient an actor of his/her treatment. The possibility to control the lithium level with a device that can be used at home would favor this involvement. Although the main part of the work to produce a device is research and development, regulatory analysis, including usability, should not be neglected. Indeed, some design choices should be made taking into account usability constraints. This ensure the fabrication of a device which will be safe, effective and well accepted by the intended users. In this conference, we present actions taken in this direction during the R-Link project.