Study Comparing Outcomes for Patients With Treatment Resistant Depression Who Receive VNS Therapy at Different Doses

Inclusion Criteria

• Patient has a diagnosis of chronic or recurrent depression and is currently experiencing a major depressive episode.
• Patient has not had an adequate response to four or more adequate antidepressant treatments from at least two different antidepressant treatment categories.
• Patient has (in the investigator's judgment) sufficient impairment from his/her depression and/or depression treatment that the potential benefits/risks of VNS Therapy are warranted.
• Patient must currently be receiving at least one antidepressant treatment; the patient must be receiving all current antidepressant treatments in a stable regimen.
• If the patient has a current diagnosis of bipolar disorder, the patient must be receiving a mood stabilizer.
• Patient must be 18 years of age or older and of legal age of consent.
• Patient must be able to complete the evaluations specified in the study procedures flow chart.
• Patient must provide written informed consent and Health Insurance Portability and Accountability Act (HIPAA) authorization.

Exclusion Criteria

• Patient has had a bilateral or left cervical vagotomy.
• Patient currently uses, or is expected to use during the study, short-wave diathermy, microwave diathermy, or therapeutic ultrasound diathermy.
• A VNS Therapy System implant would pose an unacceptable surgical or medical risk for the patient.
• Patient is expected to require full body magnetic resonance imaging during the clinical study.
• Patient is acutely suicidal.
• Patient has a history of schizophrenia, schizoaffective disorder, or other psychotic disorder or a current major depressive episode that includes psychotic features (commonly referred to as psychotic depression).
• Patient has a history of rapid cycling bipolar disorder or a current diagnosis of bipolar disorder mixed phase.
• Patient has a history of borderline personality disorder.
• Patient has a history of drug or alcohol dependence within the 12 months prior to the baseline visit or currently takes a narcotic drug five or more days per week.
• Patient is currently enrolled in another investigational study.
• Patient has had a prior VNS Therapy System implant.

Note: Some IRBs may require additional conditions for enrollment.