Determine bioequivalence between branded and generic bupropion extended release (XL) products (and between generic products) at steady state in patients with major depressive disorder.

The protocol is a prospective, randomized, double-blinded, crossover study with Major Depressive Disorder (MDD) receiving bupropion HCl 300mg XL (branded or generic).

Subjects will be studied in 4 phases for a total of approximately 28 weeks:

Phase 1: an approximately 4-week lead-in phase during which participants remain on their existing bupropion product Phases 2 - 4: randomized cross-over phases of approximately 6 weeks on each of the four bupropion study drugs (brand and 3 generics).

Inclusion Criteria

Each subject must meet all of the following criteria:

1. Adult outpatients age 18-75 years
2. Currently on once daily bupropion HCl 300mg XL (brand or any generic), for a minimum of 4 months
3. Major depressive disorder (MDD), in partial or full remission for at least 4 months, as confirmed by the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID). Spontaneous relapse of depression unrelated to medication changes is less likely - about 5% chance per year - after remission has been maintained for at least 4 months.2
4. Ability to understand and willingness to comply with study procedures, and to provide written informed consent

Exclusion Criteria

Subjects will not be enrolled if any of the following criteria exist:

1. Remission from depression not clearly attributed to bupropion treatment
2. Current severe side effects attributable to bupropion
3. Poor adherence to bupropion treatment per patient self- report and history of refill persistence
4. History of active seizure disorder, or seizure treatment within past year
5. History of significant hepatic or renal disease, based on physician assessment
6. Currently taking drugs or natural products known to influence cytochrome P450B6 (CYP2B6) activity
7. Currently taking drugs for hepatitis C or multiple sclerosis, due to their ability to cause depression
8. Dementia or other significant cognitive impairment, per diagnosis or investigative team's assessment
9. Lifetime diagnosis of schizophrenia, schizoaffective or schizophreniform dis-order, delusional disorder, or current psychotic symptoms diagnosed by SCID
10. Abuse of or dependence on alcohol or other substances within the past 6 months as determined by SCID, and confirmed by study physician interview
11. Current suicidal ideation

28 weeks

The randomization table will be generated by the Barnes-Jewish Hospital Investigational Pharmacy. Each subject will be assigned the next available number. Subjects, investigators, and all study team members will be blinded to drug treatment. In the case of dropouts (either subject- or investigator-initiated), subjects will be replaced, to provide the required number of subjects.