This is a 20-subject, dose finding study to examine the use of external trigeminal nerve stimulation (TNS) as an adjunctive treatment for adults with major depressive disorder (MDD) co- occurring with posttraumatic stress disorder (PTSD) when added onto antidepressant medications. Our primary objective is the examination of TNS in this patient population.

To accomplish our specific aims, the investigators will test the following specific hypotheses:

1. Subjects will show improvement in ratings of mood, PTSD, and other symptoms during the eight-week period.
2. Subjects will show improvement in ratings of life functional capacity and quality of life with TNS.
3. Subjects will report the TNS treatments to be acceptable in terms of side effects and burden of using the device.

A total of 20 subjects with Major Depressive Disorder (MDD) co-occurring with Post Traumatic Stress Disorder (PTSD), ages 18 to 75 years, will be consented and join this project at UCLA.

The project will use TNS in under open-label conditions, using the same stimulation parameters as have been used in prior studies in MDD by itself and in treatment-refractory epilepsy. Subjects will be seen every two weeks during the 8 week study. At the end of the 8 weeks, the TNS systems will be returned and the adjunctive treatment will end. The co-primary endpoints are the changes in depression severity and in PTSD severity from enrollment to the week 8 visit.

Inclusion Criteria

1. Outpatients with non-psychotic, unipolar Major Depressive Disorder AND Posttraumatic Stress Disorder, assessed via the MINI structured interview
2. A score of ≥ 14 on the HAM-D17 with Item 1 (depressed mood) ≥ 2
3. A score of ≥ 50 on the CAPS (Clinical-Administered PTSD Scale for DSM-IV)
4. A history of treatment failure with at least one adequate trial of an antidepressant over the previous 6 weeks, 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)
5. Age range: 18 to 75. 6) 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.

Exclusion Criteria

1. Patient is mentally or legally incapacitated, unable to give informed consent.
2. 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); acute risk for suicide or self-injurious behavior. Patients with diagnostic uncertainty or ambiguity (e.g. rule-out pseudodementia of depression) will be excluded.
3. Patients with exposure to ECT or VNS within the past 6 months.
4. 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.
5. current pregnancy, breast feeding, plans to become pregnant in the 12-week treatment phase of the study, or not using a medically accepted means of contraception.
6. Other medical contraindications to any of the study procedures