Every day, people around the world drink 1.6 billion cups of coffee—and nearly twice as many cups of tea.

Yet, coffee has long been misunderstood. It has been wrongly accused of causing dehydration, thanks to a nearly century-old study from 1928—a study that only involved three participants yet somehow became an unquestioned authority on the subject.

If you’ve ever had coffee and soon after felt the urge to sprint to the bathroom, you might have assumed that it’s stripping water from your body. After all, coffee is a diuretic, and diuretics make you urinate more—so it must be dehydrating, right?

Let’s see.

So, Does Coffee Really Dry You Out?

If you feel the urge to visit the restroom after drinking coffee, you’re not imagining it. Coffee is a diuretic, meaning it increases urine production. However, just because you urinate more doesn’t mean your body is losing more water than it takes in.

A 2014 study in PLOS ONE found that moderate coffee consumption provides similar hydration levels to water (Killer et al., 2014). Another 2016 study in the Journal of Science and Medicine in Sport concluded that caffeine does not cause dehydration in healthy adults, even during exercise (Goulet et al., 2016).

In other words, your daily cup (or three) isn’t leaving you parched—it’s actually keeping you hydrated.

Caffeine and Its (Slight) Diuretic Effect

Caffeine is the main compound in coffee responsible for its diuretic properties. It stimulates the kidneys to produce more urine, but at normal intake levels, this effect is mild.

So how much is too much?

According to dietitian Maria Sorbara Mora, a significant diuretic effect only occurs at doses exceeding 500 milligrams of caffeine—equivalent to roughly five cups of coffee. If you’re drinking less than that, your body retains most of the fluid from your coffee.

For regular coffee drinkers, the body builds a tolerance to caffeine’s diuretic effects. Over time, you won’t urinate more than usual compared to non-regular drinkers (Maughan & Griffin, 2003).

Wait—Does Coffee Actually Hydrate You?

Yes, coffee contributes to daily fluid intake.

Since coffee is about 98% water, it offsets its own mild diuretic effect.

For example, consuming 300 milligrams of caffeine (about three cups of coffee) may cause the body to produce just over 100 milliliters of extra urine—far less than the total liquid you’re drinking (Grandjean et al., 2000). This means coffee still contributes to your daily fluid intake.

So, the next time someone tells you that coffee “doesn’t count” toward hydration, you can confidently correct them.

How Much Is Too Much?

According to the FDA, the recommended daily caffeine limit is 400 milligrams—about four to five cups of coffee. For most adults, this amount is safe and does not cause dehydration.

However, some individuals are more sensitive to caffeine and may experience:

  • Insomnia
  • Headaches
  • Digestive issues
  • Increased heart rate

Should Everyone Be Drinking Coffee Freely?

  • Pregnant individuals should limit caffeine to under 200 milligrams per day (American College of Obstetricians and Gynecologists).
  • Athletes should monitor caffeine’s effect on sweat rate and electrolyte balance, especially in endurance sports (Maughan & Burke, 2002).
  • People with kidney disease may experience heightened diuretic effects and should consult their doctor.

Signs You Need More Hydration

While coffee alone is unlikely to cause dehydration, it’s still important to listen to your body. If you consume high amounts of caffeine or experience coffee’s laxative effects, watch for these signs:

  • Extreme thirst
  • Dark or strong-smelling urine
  • Dry mouth, lips, or tongue
  • Dizziness or fatigue
  • Sunken eyes
  • Rapid heart rate

If you notice these symptoms, increase your water intake and balance coffee consumption with other hydrating fluids.

Coffee Is More Than Just a Morning Ritual

For decades, coffee has been unfairly demonized. But research now shows that coffee offers many health benefits beyond hydration:

  • Rich in antioxidants – Coffee contains polyphenols that fight inflammation and protect your cells (Grosso et al., 2015).
  • Boosts alertness and mood – Caffeine enhances focus, mental clarity, and reaction times (Smith et al., 1999).
  • Supports metabolism – Coffee may aid fat burning and increase energy expenditure (Hodgson et al., 2013).
  • Reduces disease risk – Studies suggest coffee may lower the risk of type 2 diabetes, Parkinson’s, and certain cancers (Lopez-Garcia et al., 2006).

With all these benefits, it’s clear that coffee is more than just a morning ritual—it’s a healthful drink when consumed in moderation.

No, Coffee Won’t Dry You Out

For too long, coffee has carried an undeserved bad reputation when it comes to hydration. But science tells a different story: Moderate coffee consumption does not dehydrate you—it hydrates you.

The problem with that outdated study is that it didn’t account for regular coffee drinkers—people whose bodies adjust to caffeine’s effects. More recent research debunks the myth, showing that moderate coffee consumption may even contribute to your daily hydration.

So, if you love your morning cup, drink it guilt-free.