Schizophrenia is a severe mental disorder associated with significant impairments in affective, cognitive and social functioning. Consequently, a special interest in the prevention of schizophrenia and psychotic disorders has emerged. Pharmacological as well as psychological interventions show promising preventive effects. The purpose of this multicentric study is the investigation of possible preventive effects of a treatment combination containing a psychotherapy form and medication (N-Acetylcytein - NAC) in individuals with an enhanced risk for developing schizophrenia. Both treatment forms may reduce the risk in this population due to their specific properties: The psychotherapy can improve social skills, whereas NAC is supposed to develop its protective effects on neuronal level due to its antiinflammatory properties. We will investigate the preventive effects by measuring transition rates to psychosis after treatment as well as improvements in social, affective and cognitive functioning.