Visit 4: After the participants have completed their medication course on the morning of this visit day, they will return to have cognition and mood reassessed; completing all previously administered assessments excepting the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders (SCID). Vital signs will be taken and blood will be drawn to assess CMP, CBC, cortisol and phenytoin levels. Participants will now enter a "washout" period of this medicine combination (approximately 3 weeks) before returning for their next visit. For those participants offered the MRI scans, their visit will extend to approximately 3 hours.