Alcohol is the most dehydrating common beverage, but it’s not the only one that can work against your fluid balance. Several popular drinks, from cocktails to energy drinks to sugary sodas, can increase urine output or pull water from your cells in ways that leave you with less usable fluid than you started with. The effect depends on what’s in the drink, how much you consume, and how accustomed your body is to the ingredients.
Alcohol: The Strongest Dehydrating Effect
Alcohol dehydrates you through a specific hormonal mechanism. It suppresses vasopressin, the hormone that tells your kidneys to hold onto water. When vasopressin drops, your kidneys let more water pass through into your urine instead of reabsorbing it back into your bloodstream. This is why you urinate so frequently when drinking, and why that urine tends to be pale and high-volume, a sign your body is flushing fluid it would normally keep.
The higher the alcohol content, the stronger this effect. A glass of beer, which is mostly water with a relatively low alcohol percentage, replaces more fluid than it costs you. A shot of liquor or a strong cocktail does the opposite. Spirits served with minimal mixers are the worst offenders because there’s very little water in the glass to offset the diuretic hit. Mixed drinks with large amounts of sugary syrup compound the problem further, adding a second dehydrating mechanism on top of the alcohol itself.
Researchers have tried to identify an exact alcohol threshold where a drink flips from hydrating to dehydrating. A rapid evidence review by the UK Health Security Agency found that no study has established a clear dose-response relationship between alcohol intake and dehydration. In practical terms, this means there’s no magic number of drinks that’s “safe” for hydration. The effect builds gradually, and factors like body size, how fast you drink, and whether you’re eating all shift the equation.
Energy Drinks: Caffeine and Sugar Combined
Energy drinks are a uniquely potent combination for fluid loss. Many popular brands pack 200 milligrams of caffeine or more into a single can, roughly equivalent to six cans of cola. That caffeine stimulates your kidneys to produce more urine. At the same time, the high sugar content in many formulas triggers a separate process: sugar molecules in your bloodstream pull water out of your cells through osmosis, and when excess sugar spills into urine, it drags water along with it.
As Columbia University researchers have noted, caffeine and sugar “double up” in energy drinks, leading to quicker dehydration than either ingredient would cause alone. This doesn’t mean a single energy drink will leave you severely dehydrated, but it does mean that relying on them as your primary fluid source, especially during exercise or hot weather, is counterproductive. The stimulant effect can also mask the early signs of dehydration like fatigue and lightheadedness, making it easy to underestimate how much water you actually need.
Coffee and Tea: Less Risky Than You Think
Caffeine on its own is a mild diuretic, but coffee and tea are mostly water. For most regular drinkers, the fluid in a cup of coffee more than compensates for the small increase in urine production the caffeine causes. The Mayo Clinic confirms that the fluid in caffeinated drinks generally balances the diuretic effect at typical caffeine levels.
The exception is high doses of caffeine consumed all at once, particularly if you’re not a habitual caffeine user. Someone who rarely drinks coffee and then has three cups in a row will experience a noticeably stronger diuretic effect than someone who drinks coffee daily. Your body builds tolerance to caffeine’s effect on urine output over time, which is why regular coffee drinkers don’t see meaningful dehydration from their usual intake. A standard cup or two of coffee or tea counts toward your daily fluid intake, not against it.
Sugary Drinks and Osmotic Fluid Loss
Beverages with very high sugar concentrations can contribute to dehydration through a process called osmotic diuresis. When blood sugar rises sharply, the excess glucose that your kidneys filter out pulls additional water into the urine, increasing the volume you lose. This is the same mechanism that causes frequent urination in unmanaged diabetes, but it can happen on a smaller scale when you drink large quantities of heavily sweetened beverages.
Regular sodas, sweetened iced teas, fruit punch, and other drinks with high sugar loads are the main culprits. In moderate amounts, they still contribute to overall hydration because they’re largely water. But when consumed in large quantities, particularly in place of water during physical activity or heat exposure, the sugar content starts to work against you. Diet sodas sidestep the osmotic issue by using artificial sweeteners, though UCLA Health notes they’re still not an ideal hydration choice compared to water.
What Actually Hydrates Well
All beverages contribute some fluid to your daily total, even the ones with mild dehydrating properties. The practical question is how efficiently they hydrate you relative to what they cost in fluid loss. Water is the baseline: 100% of what you drink stays available. Milk actually hydrates slightly better than water because its natural balance of sodium, potassium, and small amounts of sugar helps your body retain fluid longer.
Sports drinks with moderate electrolyte content and low sugar work well during prolonged exercise. Herbal teas and diluted fruit juices are close to water in their hydrating effect. Sparkling water hydrates identically to still water, despite the common misconception that carbonation somehow reduces absorption.
The drinks that meaningfully push you toward dehydration share one or more of three characteristics: high alcohol content, large doses of caffeine without much accompanying water, or heavy sugar loads. If you’re drinking any of these, matching each serving with a glass of water is the simplest way to stay ahead of the fluid loss.