Ketamine for Obsessive-Compulsive Disorder

Inclusion Criteria: * Primary diagnosis of obsessive-compulsive disorder * A score of 16 or higher on the Yale-Brown Obsessive Compulsive Scale and ability to provide written informed consent * At least one previous treatment for OCD Exclusion Criteria Experimental Group: * Any history of current or past psychotic disorder * A manic episode within the preceding three years * Current or unstable remitted substance abuse or dependence except nicotine * Pregnancy or elevated risk of becoming pregnant during study duration (desire to have children) and refusal to utilize a proper method of contraception * Any current severe personality disorder except comorbid anankastic personality disorder * Morbus Raynaud * Inability to follow the study protocol or adhere to operational requirements * Current and unstable suicidality * Unstable hypertension * Untreated hyperthyroidism * Any unstable cardiovascular disease * Untreated disorders severely affecting the HPA-axis (M.Addison, M.Cushing) * Current pharmacological therapy severely affecting the HPA-axis like corticosteroids or ACTH Exclusion Criteria Treatment as Usual Group: * Any history of current or past psychotic disorder * A manic episode within the preceding three years * Current or unstable remitted substance abuse or dependence except nicotine * Any current severe personality disorder except comorbid anankastic personality disorder * Current and unstable suicidality