Investigation of Antidepressant Efficacy of Oral Ketamine Treatment

Inclusion Criteria: * Diagnosis of a major depressive episode in the scope of a major depressive or bipolar disorder supported by a Structured Clinical Interview for DSM-IV-TR (SCID) * Hamilton depression rating scale score ≥ 19 * Willingness and competence to sign the informed consent form * Stable psychopharmacological treatment for 10 days (except benzodiazepines) Exclusion Criteria: * Initiation of a new antidepressant or mood stabilizing treatment (pharmacological, physical or psychotherapeutic) with adequate dosage (as defined by the minimum recommended dose in the respective prescribing information) within 4 weeks prior to inclusion * Prior use of ketamine * Pregnancy/Breast feeding * Instable arterial hypertension \>170/110mmHg * Hepatic dysfunction * Hyperthyreosis * History of glaucoma * Neurodegenerative disorders * Any unstable medical illness * History of substance abuse within the past 12 months * History of psychosis * Failure to comply with the study protocol or to follow the instructions of the investigating team * Current treatment with one of the following drugs: clopidogrel, carbamazepine, valproate, barbiturates, memantine, modafinil, disulfiram, amiodarone, ranolazine, phenytoin, verapamil, fibrates, antiretroviral agents, antimicrobial chemotherapeutics, azole antifungals, glucocorticoids, cyclosporine, valeriana/garlic/grapefruit preparations, St. John's wort.