Ursodeoxycholic acid (UDCA), also known as ursodiol, is a secondary bile acid, produced in humans and most other species from metabolism by intestinal bacteria. It is synthesized in the liver in some species, and was first identified in bile of bears of genus Ursus, from which its name derived. In purified form, it has been used to treat or prevent several diseases of the liver or bile ducts. It is available as a generic medication. Medical uses UDCA has been used as medical therapy in gallstone disease (cholelithiasis) and for biliary sludge. UDCA helps reduce the cholesterol saturation of bile and leads to gradual dissolution of cholesterol-rich gallstones. UDCA may be given after bariatric surgery to prevent cholelithiasis, which commonly occurs due to the rapid weight loss producing biliary cholesterol oversaturation and also biliary dyskinesia secondary to hormonal changes. Primary biliary cholangitis UDCA is used as therapy in primary biliary cholangitis (PBC; previously known as primary biliary cirrhosis) where it can produce an improvement in biomarkers. Meta-analyses have borne out conflicting results on the mortality benefit. However analyses that exclude trials of short duration (i.e. < 2 years) have demonstrated a survival benefit and are generally considered more clinically relevant. A Cochrane systematic review in 2012 found no significant benefit in reducing mortality, the rate of liver transplantation, pruritus or fatigue. Ursodiol and obeticholic acid are FDA-approved for the treatment of primary biliary cholangitis. Primary sclerosing cholangitis UDCA use is associated with improved serum liver tests that do not always correlate with improved liver disease status. WHO Drug Information advises against its use in primary sclerosing cholangitis in unapproved doses beyond 13–15 mg/kg/day. UDCA in a dose of 28–30 mg/kg/day increases risk of death and need for liver transplant by 2.3-fold among those with primary sclerosing cholangitis, despite decrease in liver enzymes. Intrahepatic cholestasis of pregnancy UDCA has been used for intrahepatic cholestasis of pregnancy. UDCA lessens itching in the mother and may reduce the number of preterm births. Effects on fetal distress and other adverse outcomes are unlikely to be great. Cholestasis UDCA use is not licensed in children, as its safety and effectiveness have not been established. Evidence is accumulating that ursodeoxycholic acid is ineffective, unsafe and its use is associated with significant risk of morbidity and mortality in neonatal hepatitis and neonatal cholestasis. Other conditions UDCA has been suggested to be an adequate treatment of bile reflux