This study is being conducted to evaluate how the body absorbs and processes the sustained release (SR) and extended release (XL) medication bupropion (Wellbutrin®). Subject who are 1-3 years post gastric bypass surgery will be invited to participate. Non-surgical controls will also be enrolled based on a matching criteria to post gastric bypass subjects. Participants will be asked to complete two 12-hour study days approximately 11 days apart.

Inclusion Criteria:

1. Male or Female
2. Age 18-65 (inclusive, at time of informed consent)
3. No tobacco use in the past three months.
4. Underwent Roux-en-Y Gastric Bypass weight loss surgery 12-36 months prior to study OR has not had a weight loss surgery but matches the gastric bypass patients on age, gender, and BMI.
5. Ability to read, write and understand English

Exclusion Criteria:

1. Taking a medication that has a clinically significant interaction with bupropion or an interaction that may alter the study data.
2. Hypersensitivity to bupropion or any excipient contained within the dosage forms.
3. Inability to tolerate repeated blood draws.
4. Any history of bipoloar disorder or a psychotic disorder.
5. Current major depressive disorder or current suicidality.
6. Alcohol or substance dependence in the past year.
7. Currently pregnant or lactating or unwillingness to use medically accepted contraception during study
8. Taking a medication which significantly alters gastrointesinal transit time or significantly reduces acid secretion (e.g. routine use of proton pump inhibitors, H2 antagonists, sucralfate).
9. Medical conditon which may increase participant risk with bupropion (e.g., history of significant head injury, seizure disorder, etc.)
10. Self reported history of viral hepatits or HIV.
11. Positive urine drug screen unless documented prescription of a non-interacting medication.
12. History of seizures or epilepsy or other conditions which may increase seizure risk with bupropion as described in the package insert (e.g. history of significant head injury, alcoholism, etc).
13. History of eating disorder such as anorexia nervosa or bulimia.
14. Renal impairment as evidenced by an estimated glomerular filtration rate of less than 60 ml/min/1.73 m2 as reported by the laboratory, or any other abnormality on a renal panel that the medical provider feels puts the participant at risk or may compromise the study data
15. Hepatic insufficiency as defined by any hepatic enzyme greater than 3x the upper limit of normal or other hepatic laboratory abnormalities at the discretion of the medical provider.
16. Any significant electrolyte abnormality on a basic metabolic panel that the medical provider feels may put the subject at risk of a seizure from bupropion.