This study is being conducted to evaluate how the body absorbs and processes the immediate release (IR) and sustained release (XR) medication venlafaxine (Effexor®). Subject who are 1-3 years post gastric bypass or sleeve gastrectomy 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. This study will enroll up to 30 participants.