Why does coffee help with digestion?

Ask the doctor

Q. I love my morning cup of joe, but I've noticed it also sends me straight to the bathroom for a bowel movement. Why can coffee have a laxative effect?

A. Since about half of American adults profess to drink coffee every day, this perennially popular drink must boast some pretty compelling benefits. Beyond waking up our brains, coffee also helps jolt some people's digestive tracts.

This happens for several reasons. A 2021 study suggests that two hormones coffee boosts — gastrin and cholecystokinin — trigger the so‑called gastrocolic reflex, prompting the colon to contract and move waste through the rectum. Since colon contractions tend to be strongest in the morning anyway, drinking coffee plays into this natural digestive process. This hormonal action is specific to coffee, not tea or other drinks, but coffee's caffeine content heightens this effect by increasing colon contractions and stool movement. For some people, this can happen within minutes; for others, it might take hours — or not happen at all.

On the other hand, people who tend to be constipated often find that their morning cup of coffee helps keep them regular. But don't drink excessive amounts of coffee just for this reason. It can make us jittery or worsen the symptoms of certain conditions, including irritable bowel syndrome, glaucoma, or overactive bladder.