Mobile health interventions are regarded as affordable and accessible tools that can enhance standard psychiatric care. As part of the mHealth Psycho-Educational Intervention Versus Antipsychotic-Induced Side Effects (mPIVAS) project (www.psylog.eu), we developed the mobile application "PsyLOG" based on mobile "smartphone" technology to monitor antipsychotic-induced side effects. The aim of this paper is to describe the rationale and development of the PsyLOG and its clinical use. The PsyLOG application runs on smartphones with Android operating system. The application is currently available in seven languages (Croatian, Czech, English, French, German, Japanese and Serbian). It consists of several categories: "My Drug Effects", "My Life Styles", "My Charts", "My Medication", "My Strategies", "My Supporters", "Settings" and "About". The main category "My Drug Effects" includes a list of 30 side effects with the possibility to add three additional side effects. Side effects are each accompanied by an appropriate description and the possibility to rate its severity on a visual analogue scale from 0-100%. The PsyLOG application is intended to enhance the link between patients and mental health professionals, serving as a tool that more objectively monitors side-effects over certain periods of time. To the best of our knowledge, no such applications have so far been developed for patients taking antipsychotic medication or for their therapists.