Intra-nasal vs. Intra-venous Ketamine Administration

Inclusion Criteria: 1. Age 18-65 2. Diagnosis of MDD (Major Depressive Disorder), made or affirmed by a senior psychiatrist in Shalvata 3. MADRS score \> 20 4. Treated with conventional anti-depressant, administered within a formal psychiatric clinic or by a certified psychiatrist. Exclusion Criteria: 1. Active or past psychotic disorder, including a history of psychotic affective state 2. Mental Retardation or Autistic Spectrum Disorder 3. Prominent personality disorder 4. Cardiac or neurologic active medical condition, including past CVA/TIA (Cardiovascular Accident/Transient Ischemic Attack) or any other unstable medical condition. 5. Chronic nasal congestion 6. Active or recent drug or alcohol abuse 7. Substantial suicidality in a patient requiring admission but refuses to do so, and signs an "against medical advice" release form as part of clinical evaluation, and does not answer the terms for involuntary admission.