Celsius contains a combination of caffeine, herbal extracts, artificial sweeteners, and other compounds that each independently speed up your digestive system. When you drink them all together in one can, the combined effect can send you to the bathroom within minutes. You’re not imagining it, and you’re definitely not alone.
Caffeine Triggers Your Colon Muscles
A single can of Celsius contains 200 mg of caffeine, roughly equivalent to two cups of coffee. Caffeine stimulates peristalsis, the wave-like muscle contractions that push food and waste through your intestines. It does this by activating receptors on the smooth muscle cells lining your colon, essentially telling those muscles to squeeze and move things along faster.
This effect is dose-dependent. At 200 mg in one sitting, especially if you drink the can quickly, the caffeine hits your system fast and triggers a strong contractile response. If you’re not a regular caffeine consumer, the effect is even more pronounced. Your body hasn’t built tolerance, so the muscles in your gut react more dramatically to the stimulation.
Interestingly, research in rats found that even decaffeinated coffee stimulated gut muscle contractions to a similar degree as regular coffee, suggesting other compounds in coffee (and potentially in energy drink blends) contribute to the effect through the same nerve and muscle pathways. The caffeine in Celsius isn’t the only thing pushing your gut into action.
Guarana and Green Tea Add More Stimulation
Celsius contains a proprietary blend called MetaPlus, which includes guarana extract and green tea leaf extract alongside the listed caffeine. Guarana seeds naturally contain caffeine, so they add to the total stimulant load even beyond what’s listed on the label. At higher doses, guarana acts as a natural laxative by further stimulating those same intestinal contractions.
The exact amount of guarana and green tea in each can isn’t disclosed individually. The entire MetaPlus blend totals 1,810 mg, but the breakdown between ingredients is proprietary. What matters is that these plant extracts contain their own bioactive compounds that can independently irritate or stimulate the gut lining, compounding the effect of the caffeine already in the drink.
Artificial Sweeteners Pull Water Into Your Gut
Celsius is marketed as having no sugar, which means it relies on artificial sweeteners like sucralose and sugar alcohols like erythritol to taste sweet. Your body can’t fully digest these compounds, and that’s where the trouble starts.
When undigested sweeteners sit in your intestines, they draw water in through osmosis, the same basic mechanism behind over-the-counter laxatives. This extra fluid loosens your stool and speeds up transit time. Sugar alcohols also get fermented by gut bacteria, producing gas, bloating, and that urgent feeling. Erythritol is milder than some other sugar alcohols, mainly causing nausea and gas at large doses rather than full-blown diarrhea. But combined with everything else in a can of Celsius, even a mild osmotic effect can tip the balance.
Ginger Extract Speeds Things Up Too
The MetaPlus blend also contains ginger extract. Ginger has been used for centuries to treat nausea and indigestion, and part of how it works is by accelerating gastric emptying, meaning food and liquid leave your stomach faster. In a normal context, this is helpful. But when your stomach empties quickly into an intestine already being stimulated by caffeine and irritated by sweeteners, the result is a faster trip from mouth to toilet.
Drinking It Cold and Fast Matters
Most people drink Celsius chilled and fairly quickly, often on an empty stomach before a workout. Cold liquids can stimulate the gastrocolic reflex, a natural response where your stomach stretching triggers your colon to start making room by moving its contents along. On an empty stomach, there’s nothing to slow the absorption of caffeine and other active ingredients, so they hit your system at full strength.
Caffeine also mildly increases urine production, which can shift your body’s fluid balance. The Mayo Clinic notes that the fluid in caffeinated drinks generally offsets this diuretic effect, but high doses taken all at once (like a full 200 mg can) are more likely to cause loose stools and upset stomach, particularly in people who aren’t regular caffeine users.
Why Some People Are More Affected
Not everyone who drinks Celsius will experience this. Several factors determine how strongly your gut reacts:
- Caffeine tolerance: Daily coffee drinkers have partially desensitized gut receptors, so the same 200 mg produces a weaker response than it would in someone who rarely consumes caffeine.
- Sweetener sensitivity: Some people ferment sugar alcohols more aggressively than others, depending on their gut bacteria composition. If artificial sweeteners in other products bother you, Celsius likely will too.
- Empty stomach: Drinking Celsius without food means nothing buffers or slows the absorption of its active ingredients.
- Individual gut sensitivity: People with irritable bowel syndrome or other functional gut conditions have heightened nerve responses in their intestines, making them more reactive to any stimulant.
How to Reduce the Effect
If you like Celsius but don’t love the bathroom trips, the simplest fix is to eat something before or while you drink it. Food slows gastric emptying and gives your intestines something to work with besides a concentrated blend of stimulants and sweeteners. Drinking the can more slowly, over 30 to 45 minutes rather than all at once, also spreads out the caffeine absorption and reduces the intensity of the gut response.
Switching to a half can is another option. At 100 mg of caffeine with proportionally less of every other ingredient, you may stay below your personal threshold for triggering that laxative cascade. Over time, if you drink Celsius regularly, your body will also build some tolerance to the caffeine component, though the sweetener effect doesn’t diminish the same way.