Coffee may cause a laxative effect in some people. Drinking it in the morning may also trigger the gastrocolic reflex that may stimulate a bowel movement.

Coffee is more than just a beverage; for many people, it’s their life’s blood. And while coffee is primarily known for “waking up” the brain, many people claim that their morning cup of java also energizes their bowels. So, what is it about coffee that makes some people run for the nearest toilet while others feel no impact? Read on to learn more.

In short, there aren’t recent scientific studies on how coffee influences bowel habits. But one 2015 study did point out that decaffeinated coffee had a significant effect on bowel movements for those with postoperative ileus, compared to caffeinated coffee and water. Postoperative ileus refers to digestive problems that occur after abdominal surgery. In this case, the patients studied had colon surgery.

There are some earlier studies from the 1990s that address the possible connection between coffee and digestion. According to a 1990 questionnaire study, drinking caffeinated or decaffeinated coffee increased rectosigmoid motility. This is the movement at the intersection of the large colon’s end and the upper rectum. The study found that this movement increased within four minutes in about 29 percent of participants, while drinking plain hot water did not have the same effect.

A 1998 study found that caffeinated coffee, decaf coffee, and a 1,000-calorie meal all stimulated the colon. However, caffeinated coffee stimulated the colon 23 percent more than decaf coffee and 60 percent more than plain water.

While coffee may have a laxative effect in some people, whether it’s the coffee or the caffeine is unclear. Coffee’s effect is not solely due to caffeine, since decaf coffee has shown the same or an even greater effect. In addition, most people don’t have to poop after drinking other caffeinated beverages, such as soda or energy drinks. Still, according to the International Foundation for Functional Gastrointestinal Disorders (IFFGD), excessive consumption of any caffeinated drink may cause loose stools or diarrhea. And caffeine within coffee can act as a stimulant, which might induce bile production that increases bowel movements.

The IFFGD also indicates that some artificial sweeteners, and lactose, may have a laxative effect. Lactose is a type of sugar found in dairy products. If your body doesn’t make enough of the enzyme needed to digest lactose, you may experience symptoms such as diarrhea. Artificial sweeteners also can cause diarrhea. So, if you add significant amounts of cream and sugar to your coffee and find yourself on the toilet a short time later, it may be due to the lactose or other sugars, not the coffee itself.

The simple act of drinking coffee or any other beverage in the morning stimulates a defecation reflex known as the gastrocolic reflex. This reflex helps jump-start your bowels whenever you eat or drink. No scientific evidence exists showing that this is why you have a bowel movement after drinking coffee. However, for people with irritable bowel syndrome that have a hypersensitive gastrocolic reflex, research suggests that the potential laxative effect of coffee may stimulate bowel movements after drinking a cup of joe.

Some people believe drinking a warm or hot drink upon waking stimulates the digestive system and leads to a bowel movement. According to gastroenterologist Felice Schnoll-Sussman in a Runner’s World article, “It [the warm liquid] widens blood vessels in the digestive system and helps increase blood flow and GI activity.” Since everyone doesn’t need to hit the bathroom after drinking a warm beverage, there may also be other factors at play.

It may be argued that coffee can’t be called a laxative because it’s a diuretic. In other words, if coffee makes you urinate more and lose fluid, it’s more likely to cause dehydration and induce constipation than trigger a bowel movement. Not so, per a 2014 study. Testing only males, this study found that a moderate intake of coffee does not lead to dehydration and may actually help people meet their daily fluid intake requirement.

A coffee enema is a colon cleanse. It’s a remedy said to relieve constipation and reduce general toxicity in the body. The process involves pumping a combination of cooled, freshly brewed coffee and water into your colon via an enema bag and then releasing it. Any subsequent bowel movements are likely caused by the sheer volume of fluid stimulating rectal muscles and not the coffee.

There’s no evidence that coffee enemas detox the body. Although, like a regular enema, they may relieve constipation. Coffee enemas can be very risky and, as with other types of colon cleanses, may cause:

  • electrolyte imbalance
  • infection
  • increased risk of dehydration
  • bowel perforations

It is much safer to use a commercially prepared enema that you can buy at the drugstore.

Older research has shown that both caffeinated and decaffeinated coffee can have a laxative affect to some degree, while newer studies are geared more toward coffee’s specific roles in digestive health. It remains unclear why some people are affected while others are not. It may be due to the amount of coffee you drink, a preexisting bowel disorder, or other tummy stimulating compounds in your brew.

What’s crystal clear is that coffee isn’t going anywhere anytime soon. According to a 2015 Gallup poll, almost two-thirds of adults in the United States drink an average of 2.7 cups of coffee daily.

If you’re someone who struggles with diarrhea after drinking coffee, try to limit your intake or see if drinking half caffeinated coffee and half decaf reduces your symptoms. If not, see your doctor. You may need to avoid coffee altogether.