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.