Major depressive disorder (MDD) is a major cause of disability and affects the working age population worldwide. The prevalence is estimated to be around 10% in the general population (5% in Japan and 16% in the US). This serious disease has a major negative impact on both the individual and society. It takes several weeks, up to months, for the usual antidepressant medications to take effect, and symptom relief is achieved in only 30-40% of MDD patients. Thus, there is a strong need to improve the diagnosis and treatment of patients with depression. This project aims to develop a cost-effective and minimally invasive method to predict the response to antidepressant medication. The assay can be used in a clinical setting and represents a new diagnostic method for MDD patients with the aim of selecting the group that is sensitive to a particular antidepressant. This would prevent patients from taking a drug with no therapeutic effect for several months. The method we have developed is based on: 1. analysis of the patient's activity recorded with a bracelet; 2. analysis of genes (clock genes) in the patient's skin cells. The results will help doctors confirm the diagnosis and choose the right antidepressant treatment. Thus, shortening the duration of treatment and suffering, and giving new hope to patients with depression. In the longer term, it is possible that our method could also be applied to patients with other psychiatric conditions.