The investigators aim to recruit, in a 2-year prospective observational study, 15 to 20 year-old participants upon the initiation of SSRI treatment. During the study period, bone mineral density of the lumbar spine and whole body will be measured using dual-energy x-ray absorptiometry (DXA) and of the radius using peripheral quantitative computed tomography (pQCT). A detailed psychiatric assessment will be conducted to control for psychopathology, as a potential confounding factor affecting bone mineralization. Changes in psychiatric treatment during the follow up period will also be documented and accounted for. By using a group of controls, of comparable age and sex distribution, the investigators aim to evaluate 1) whether psychopathology, at baseline, is associated with low bone mass, 2) if treatment with SSRIs suppresses bone mineralization, and 3) if the discontinuation of the SSRI is followed by a restoration of bone mineral accrual. 4) Furthermore, genetic testing will investigate whether variants of the serotonin system genes moderate the effect of SSRI treatment on bone mineral density.