What are the side effects of d-mannose?

D-mannose is considered safe for most adults; however, it can cause loose stool and bloating, according to WebMD. High doses of d-mannose pose a risk for kidney damage.

D-mannose is a form of sugar that is related to glucose, and it is used for preventing urinary tract infections and in treating carbohydrate-deficient glycoprotein syndrome, a form of inherited metabolic disorder, notes WebMD.

The mechanism through which d-mannose treats either of these conditions has not been deeply researched; however, it is thought that in urinary tract infections it prevents certain forms of bacteria from adhering to the walls of the urinary tract, explains WebMD.