Why Can Energy Drinks Cause Diarrhea?

Energy drinks can trigger diarrhea because they combine several gut-disrupting ingredients in a single serving: caffeine that accelerates intestinal contractions, concentrated sugars that pull water into the bowel, carbonation that pushes gas through the digestive tract, and additives like taurine that alter bile acid activity. A systematic review and meta-analysis of adverse health effects found that roughly one in five adult energy drink consumers reported gastrointestinal upset, putting it among the most common complaints alongside jitteriness and insomnia.¹ The effect is rarely dangerous on its own, but understanding which ingredient is responsible can help you avoid the problem.

Caffeine Speeds Up Your Intestines

The primary culprit in most energy drinks is caffeine. A standard can contains anywhere from 80 to 300 milligrams, and caffeine is a well-documented stimulant of the gastrointestinal tract. Research measuring colon activity found that caffeinated beverages can increase motility in the lower colon within four minutes of ingestion, and the effect lasted at least 30 minutes.² In plain terms, the muscles lining your intestines start squeezing faster and harder, pushing contents through before your body has fully absorbed the water from them. The result is looser, more urgent stools.

This effect isn’t universal. In that same study, about eight of fourteen participants showed a measurable increase in colon motility, while the remaining six showed no response at all.² If coffee has never sent you to the bathroom, you might handle energy drink caffeine without much trouble. But if your gut has always been caffeine-sensitive, energy drinks are likely to cause the same or worse reaction, since many contain considerably more caffeine than a cup of coffee.

Caffeine also works through the communication network linking the brain and the digestive tract. A review of coffee’s effects on the gastrointestinal system noted pro-motility effects on the gut’s outer muscle layers, though researchers acknowledged that many of the exact pathways remain surprisingly understudied.³ So while we know caffeine makes the gut move faster, the full picture of how it does so is still being filled in.

Sugar and the Osmotic Water Rush

Many popular energy drinks contain 40 to 60 grams of sugar per can, often as sucrose or high-fructose corn syrup. When that much sugar hits your small intestine at once, it creates a concentrated solution that your body needs to dilute before it can absorb it.

High-fructose corn syrup drinks are among common hyperosmolar beverages, meaning they are more concentrated than your body’s own fluids.⁴ When a hyperosmolar liquid reaches the small intestine, the body responds by pulling water out of the bloodstream and into the bowel to dilute it. This influx of extra water is exactly what produces watery, urgent stools. The mechanism is similar to what happens in people with “dumping syndrome” after certain stomach surgeries, where the stomach empties too quickly and osmotic fluid gets trapped in the intestine.⁴ You don’t need a surgical history for a milder version of this to happen. Drinking a large, sugary energy drink on an empty stomach delivers a concentrated sugar wave to the intestine, water follows, and everything moves through faster than the colon can reabsorb it.

Fructose specifically is poorly absorbed by a substantial portion of the population. For people with some degree of fructose malabsorption, the unabsorbed fructose passes through the small intestine and reaches the large intestine, where bacteria ferment it and produce gas, bloating, and loose stools. Energy drinks sweetened with high-fructose corn syrup are a particularly effective trigger because the fructose arrives alongside caffeine that’s already accelerating transit.

Why Sugar-Free Versions Aren’t Necessarily Safer

Switching to a “zero-calorie” energy drink doesn’t automatically spare your gut. These products use artificial sweeteners like sucralose, aspartame, or acesulfame potassium, and some include sugar alcohols like sorbitol or erythritol. A systematic review examining artificial sweeteners and the gastrointestinal tract found that the two main areas of concern are gut motility and changes to the gut microbiome, though most of the available evidence comes from animal models rather than human trials.⁵

Consumer experience fills in some of the gaps that laboratory research hasn’t yet closed. Sugar alcohols in particular are well known for their laxative effect at moderate-to-large doses. They’re poorly absorbed in the small intestine, so they reach the colon mostly intact, where they draw in water through the same osmotic mechanism as excess fructose. Even artificial sweeteners that don’t have an obvious osmotic profile can cause bloating, gas, and diarrhea in some individuals, possibly through effects on the gut microbiome that researchers are still trying to characterize.

If you’ve noticed that sugar-free energy drinks cause more distress than the regular versions, the sweetener blend is the most likely explanation. And if both types bother you, caffeine itself is probably the dominant driver.

Carbonation Gets Things Moving Faster

Most energy drinks are carbonated, and the dissolved carbon dioxide plays a supporting role in digestive upset. When a carbonated beverage reaches an empty stomach, the fluid passes relatively quickly into the small intestine. There, the dissolved carbon dioxide warms to body temperature and is released as gas, converting to bicarbonate.⁶ This rapid gas release can distend the intestinal walls and stimulate the wave-like contractions that push contents along, accelerating transit time.

When your stomach already has food in it, carbonation behaves differently. The gas tends to stay in the stomach longer, accumulating and often triggering belching instead of moving into the intestines.⁶ But the typical energy drink consumption pattern, first thing in the morning or between meals, is exactly the scenario where carbonation is most likely to speed things along in the intestines rather than just producing a burp.

Taurine and Bile Acid Chemistry

Taurine is one of the signature ingredients in energy drinks, typically present in doses of 500 to 2,000 milligrams per can. Beyond its marketing as a performance booster, taurine plays multiple roles in the body, including bile acid conjugation, osmoregulation, and modulation of inflammation.⁷ The bile acid connection is the one most relevant to diarrhea.

Bile acids are what your liver produces to help digest fats. Taurine-conjugated bile acids behave differently from other forms, and shifts in bile acid composition can influence how the gut absorbs water and how quickly material moves through the colon. Animal research has found that taurine can influence gut microbiota homeostasis, though the implications of these changes in healthy humans consuming typical energy drink doses remain unclear.⁷ Taurine is more plausibly a contributing factor than a primary cause, amplifying the effects of caffeine and sugar rather than causing diarrhea on its own. For someone whose gut is already close to the threshold, though, an extra gram or two of taurine on top of everything else in the can might be enough to push things over.

The Pre-Workout Trap

Many people drink energy drinks before exercise, and that combination creates an especially hostile environment for the digestive system. During strenuous activity, blood flow is redirected away from the digestive organs toward working muscles. This gut underperfusion is the main driver of exercise-related nausea, cramping, and diarrhea.⁸

Adding an energy drink compounds the problem in two directions at once. The high sugar content slows gastric emptying, meaning the drink sits in the stomach longer and causes more discomfort when it eventually floods the intestines. A review of exercise-related GI distress noted that gastric emptying is “proportionally slowed by carbohydrate-rich (hyperosmolar) solutions.”⁸ Meanwhile, the caffeine is simultaneously accelerating intestinal motility at a time when the gut is already stressed and receiving less blood. The result is more forceful contractions in an intestine poorly equipped to handle them.

Dehydration amplifies the cycle further. Caffeine has a mild diuretic effect, exercise causes fluid loss through sweat, and diarrhea itself removes water. Athletes relying on energy drinks for pre-workout fuel can end up in a cascade where the drink causes GI distress, the distress causes fluid loss, and the fluid loss worsens the GI symptoms. A bottle of water with a modest caffeine source delivers the energy boost without the same osmotic and carbonation load.

Who Tends to Be More Sensitive

Not everyone who drinks an energy drink ends up racing to the bathroom. The variability comes down to a handful of identifiable factors.

People with irritable bowel syndrome or inflammatory bowel disease are especially vulnerable. Their guts are already primed to overreact to osmotic stress and motility stimulation, so even a moderate sugar or caffeine load from a single can can trigger a flare. Caffeine tolerance also varies enormously depending on genetics and habitual intake. People who rarely consume caffeine experience a much stronger gut-motility response than daily coffee drinkers whose receptors have partially adapted. If you’ve been caffeine-free for a while and then down a high-dose energy drink, your intestines will react more dramatically than those of someone who drinks three cups of coffee every morning.

Fructose malabsorption, as mentioned earlier, is another common but underdiagnosed factor. For affected individuals, any drink sweetened with high-fructose corn syrup can cause gas, bloating, and diarrhea regardless of the brand. The energy drink just stacks caffeine and carbonation on top of the fructose problem. Adolescents and young adults, who are among the heaviest energy drink consumers, often have less established caffeine tolerance and may be more susceptible to the combined ingredient effects than habitual coffee drinkers.

Practical Adjustments That Actually Help

If you want to keep energy drinks in your routine without the GI fallout, the fixes are mostly about timing and dosing.

• Eat first: Having food in your stomach slows the rate at which caffeine and sugar reach the intestines, blunting both the osmotic water pull and the motility spike. When the stomach is empty, fluids pass rapidly to the small intestine where they cause the most trouble.⁶
• Choose smaller cans: Many brands sell sizes from 8 to 24 ounces. Picking the smallest option cuts your exposure to every offending ingredient at once.
• Drink water alongside: Hydrating before or during your energy drink dilutes the sugar concentration reaching the intestines, reducing the body’s need to pull extra water from the bloodstream into the bowel.
• Test sugar vs. sugar-free: If sugared versions cause trouble, try sugar-free, and vice versa. If both cause problems, caffeine is the likely dominant factor, and the only real solution is a lower dose.
• Separate from exercise: If you use energy drinks for workouts, try consuming one at least 30 to 45 minutes before activity rather than immediately prior, giving your stomach time to process some of the sugar and carbonation before blood flow shifts to your muscles.

Why Energy Drinks Hit Harder Than Coffee or Soda

One reason energy drinks cause more GI complaints than either coffee or regular soda is the stacking effect. Coffee delivers caffeine, and soda delivers sugar plus carbonation, but an energy drink delivers all of these simultaneously, along with taurine, B vitamins in megadoses, and sometimes herbal extracts like guarana, which is itself an additional caffeine source that may not be fully reflected in the caffeine number on the label. The systematic review that found roughly one in five consumers reporting gastrointestinal upset was looking at energy drinks specifically, not caffeine or carbonation in isolation.¹

This stacking explains the common experience of people who handle coffee and cola perfectly well but struggle with energy drinks. If caffeine alone doesn’t push your gut past its threshold, and sugar alone doesn’t either, the combination of both plus carbonation plus taurine plus whatever else is in the formula might be enough to cross the line. Everyone has a different threshold, shaped by genetics, gut health, caffeine habits, and the contents of their stomach that day. Energy drinks are engineered to deliver maximum stimulation quickly, and the digestive system sometimes pays the price for that speed.