Double Blinded Randomized Trial of eTNS as adjuvant treatment for Major Unipolar Depressive Disorder. The primary objective is to assess the safety and tolerability of eTNS (external trigeminal nerve stimulation) of the V1 branch of the trigeminal nerve as an adjunctive treatment for adult patients with the diagnosis of unipolar MDD (Major Depressive Disorder).

Inclusion Criteria:

• Outpatients with non-psychotic, unipolar Major Depressive Disorder assessed via the MINI structured interview and legally capacitated to sign the informed consent for participation in the study;
• A score of ≥ 14 on the HAM-D17 with Item 1 (depressed mood) ≥ 2;
• A history of treatment failure with at least 3 adequate trials antidepressants over the previous 6 weeks and less than 6 medications, with no change in antidepressant medication or dose within the previous 6 weeks, and ongoing use of at least one antidepressant (which will continue during participation in the study);
• Patients with suicidal ideation are eligible only if the thoughts of death or of life not being worth living are not accompanied by a plan or intention for self-harm and lack of self-harming attempt in the past 6 months;
• Patients with appropriate support to be compliant with the study protocol.

Exclusion Criteria:

• Patient is mentally or legally incapacitated, unable to give informed consent;
• Patients with psychosis (psychotic depression, schizophrenia, or schizoaffective diagnoses (lifetime); bipolar disorder (lifetime); dementia (lifetime); delirium or any substance abuse disorder within the past 6 months; eating disorder within the past year; obsessive-compulsive disorder (lifetime); post-traumatic stress disorder within the past year; acute risk for suicide or self-injurious behavior. Patients with diagnostic uncertainty or ambiguity (e.g. rule-out pseudo-dementia of depression) will be excluded;
• Patients currently receiving more than six medications for treatment of MDD;
• Patients with exposure to ECT or rTMS or any investigational treatment (for any disorder) within the past 6 months;
• Prior VNS and/or DBS therapy (lifetime);
• Past history of skull fracture; cranial surgery entering the calvarium; space occupying intracranial lesion; stroke, CVA, or TIAs; cerebral aneurysm; Parkinson's or Huntington's disease; or Multiple Sclerosis.
• Current pregnancy, breast feeding, plans to become pregnant during the study, or not using a medically accepted means of contraception;
• Other medical conditions that would increase the risk of infection or surgical related morbidity and/or would affect compliance with the study protocol.