BackgroundIn addition to the reduction of symptomatic gallstone disease, ursodeoxycholic acid (UDCA) might also have beneficial metabolic effects after bariatric surgery. We examined the impact of UDCA on liver enzymes, hemoglobin A1c (HbA1c), lipids, and inflammation markers.MethodsPatients in the UPGRADE trial (placebo-controlled, double-blind) were randomized between UDCA 900 mg daily or placebo pills for 6 months after bariatric surgery. Patients without blood measurements pre- or 6 months postoperatively were excluded. The change in liver enzymes, Hba1c, lipids, and inflammation markers after surgery were compared between the UDCA and placebo group, followed by a postoperative cross-sectional comparison.ResultsIn total, 513 patients were included (age [mean ± SD] 45.6 ± 10.7 years; 79% female). Preoperative blood values did not differ between UDCA (n= 266) and placebo (n= 247) groups. Increase of alkaline phosphatase (ALP) was greater in the UDCA group (mean difference 3.81 U/l [95%CI 0.50 7.12]). Change in other liver enzymes, HbA1c, lipids, and CRP levels did not differ. Postoperative cross-sectional comparison in 316 adherent patients also revealed a higher total cholesterol (mean difference 0.25 mg/dl [95%CI 0.07–0.42]), lower aspartate aminotransferase (mean difference −3.12 U/l [−5.16 – −1.08]), and lower alanine aminotransferase level (mean difference −5.89 U/l [−9.41 – −2.37]) in the UDCA group.ConclusionUDCA treatment leads to a higher, but clinically irrelevant increase in ALP level in patients 6 months after bariatric surgery. No other changes in metabolic or inflammatory markers were observed. Except for the reduction of gallstone formation, UDCA has no effects after bariatric surgery.Graphical AbstractSupplementary InformationThe online version contains supplementary material available at 10.1007/s11695-023-06581-8.