IntroductionPatients living with psychiatric illnesses (PIs) have a high prevalence of obesity. In a 2006 survey, 91.2% of professionals in the bariatric field identified “psychiatric issues” as clear contraindications to weight-loss surgery.MethodsThis retrospective matched case–control study investigated the impact, safety, and possible relapse after bariatric metabolic surgery (BMS) in patients with PIs. Also, we tested the incidence of patients who developed PI after BMS and compared the post-procedural weight loss with that in a matched control group without PIs. The cases were matched in a ratio of 1:4 to the control patients standardized for age, sex, preoperative BMI, and type of BMS.ResultsOf 5987 patients, 2.82% had a preoperative PI; postoperative de novo PI was present in 0.45%. Postoperative BMI was significantly different between the groups when compared to preoperative BMI (p< 0.001). Percentage of total weight loss (%TWL) after six months was not significantly different between the case (24.6% ± 8.9) and control groups (24.0% ± 8.4,p= 1.000). Early and late complications were not significantly different between the groups. The psychiatric drug use and dosage changes did not differ significantly pre- and postoperatively. Of the psychiatric patients, 5.1% were postoperatively admitted to a psychiatric hospital (p= 0.06) unrelated to BMS, and 3.4% had a prolonged absence from work after surgery.ConclusionBMS is an effective weight loss treatment and a safe procedure for patients with psychiatric disorders. We found no change in the patients’ psychiatric status outside the usual disease course. Postoperative de novo PI was rare in the present study. Furthermore, patients with severe psychiatric illness were excluded from undergoing surgery and, therefore, from the study. Careful follow-up is necessary to guide and protect patients with PI.Graphical Abstract