What digestive function of ginger requires caution for those with a history of gallstones?

Stimulation of bile flow.

Ginger is known to act as a cholagogue or cholekinetic agent, meaning it encourages or stimulates the production and release of bile from the gallbladder into the small intestine to aid in digestion. While this effect is generally beneficial for healthy digestion, it becomes problematic for individuals who have pre-existing gallstones. If stones are present in the gallbladder or if the bile ducts are already partially obstructed, forcing the gallbladder to contract more vigorously to release increased bile volume could potentially cause existing stones to become lodged in the narrow bile ducts. This impaction can result in severe, acute pain or dangerous complications related to bile duct obstruction.