Psychiatric disorders and treatment with antidepressants SSRI/SNRI (selective serotonin reuptake inhibitors/ serotonin-norepinephrine reuptake inhibitors) are common in people with morbid obesity who are candidates for bariatric surgery. Although longitudinal assessments reveal positive effects of bariatric surgery on quality of life and mood, depressive disorders may also deteriorate after bariatric surgery. There is few and inconsistent data about the postoperative pharmacokinetics of SSRI/SNRI. The aims of our study were to provide comprehensive data about the postoperative bioavailability of SSRI/SNRI, and the clinical effects on the course of depression.

Prospective multicenter study including 63 patients (i.e. 46 participants in the bariatric surgery group, and 17 participants in the conservative group as controls) with morbid obesity and therapy with SSRI/SNRI: participants filled the Beck Depression Inventory II (BDI) questionnaire, and plasma levels of SSRI/SNRI were measured by HPLC (High Performance Liquid Chromatography), preoperatively (T0), 4 weeks (T1) and 6 months (T2) postoperatively.

Inclusion Criteria:

• Age >18 years
• BMI >35
• Existing antidepressant drug therapy with SSRI or SNRI
• Written informed consent

Exclusion Criteria:

• Taking other psychotropic drugs than SSRI/SNRI
• Active drug addiction or psychosis
• Severe depression (BDI score >30)
• Suicidality at the beginning of the study
• Gastrointestinal malabsorption
• Pregnancy

As part of the regular consultation at the obesity center of the three study sites patients were assessed for participation according to the inclusion and exclusion criteria of the study. An interprofessional team decided about the treatment, consisting of gastric bypass surgery (Roux-en-Y gastric bypass [RYGB]), sleeve gastrectomy (SG) or conservative therapy (consisting of medical visits, nutritional counseling, physiotherapy, antiobesogenic medication and psychological coaching). Afterwards, patients who had met the inclusion criteria were asked for participation, and were allocated (according to the treatment option) to the "bariatric surgery group" with the two subgroups "gastric bypass" and "sleeve gastrectomy", and to the "conservative group".