Is Coffee A Diuretic? The Answer Might Surprise You!

We all know the feeling of drinking a delicious morning brew only to find ourselves desperate to pee halfway through that early staff meeting. Surely, that means coffee is a diuretic. On the other hand, coffee is 98% water. So shouldn’t it be a source of hydration?

Is coffee dehydrating? Clearly, the answer isn’t obvious. That’s why we dug into the hard science to bring you this full report. Keep reading for the whole truth on whether coffee is a diuretic.

What Is A Diuretic?

A diuretic is any drug that increases urine production – i.e. things that make you have to pee. Diuretics work by telling your kidneys to put more water and salt into your urine. Often known as water pills, they are commonly used to treat high blood pressure or conditions that cause too much fluid to build up in your body.

Pharmaceutical diuretics are very popular. They tend to have mild side effects like frequent urination (duh), headaches, nausea, diarrhea, and dizziness. Two of the top 15 prescribed drugs in the U.S. are diuretics (1).

Is Coffee Hydrating or Dehydrating?

The confusion behind whether coffee is a diuretic stems from the fact that we often equate coffee with caffeine. Caffeine is a chemical found in coffee, but it makes up only a tiny percentage of the overall brew (about 0.04%).

Coffee is hydrating rather than dehydrating, on balance. Of course, if you’re seriously dehydrated, water is a better option than coffee for rehydration.

It Gets A Little More Complicated

Nothing is ever simple when it comes to the human body; we’re all so different. Have you heard the expression, “The dose makes the poison”? Well, that’s true in this case, too. Coffee can be dehydrating if you drink enough of it. 

According to a 2017 study, high doses of caffeine induced the diuretic effect while low doses did not. The study was relatively small, with just 8 men and 2 women. Half the participants ingested a moderate caffeine dose equivalent to about 2 and a half cups of coffee. The other five took in more than double that, equivalent to more than 5 cups of coffee. The higher dose caused diuresis, but the study concluded lower doses “do not disturb fluid balance in healthy casual coffee drinking adults at rest (2).”

A recent meta-study looked at the diuretic effect of caffeine and the impact of exercise. They initially found that an intake of 300 mg of caffeine increased urine output by an average of just 6.5 ounces (much less than the liquid taken in when drinking the coffee). So the coffee was overall hydrating. In a fascinating twice, when the subjects exercised after drinking coffee, the effect dropped to essentially zero (3).

The same study found that women were substantially more susceptible to the diuretic effect than men. Plus, there is less of a diuretic effect for regular coffee drinkers whose bodies are more accustomed to caffeine.

Coffee Diuretic Mechanism

The mechanism by which coffee acts as a diuretic is surprisingly complicated and poorly established. Researchers in a 2016 meta-analysis concluded it was related to caffeine’s ability to bind to adenosine receptors.

Caffeine is well known to block adenosine receptors in your brain. This is what causes some side effects of coffee like feeling less sleepy and more alert. But you actually have similar receptors in your kidneys and liver. It is thought that caffeine’s impact on these organs – a synergistic effect of the kidneys and liver – is what leads to the diuretic effect (4).

There is also evidence that caffeine causes increased contractions of your bladder muscle, which can make you feel the urge to pee. Learn more about that in this video with urologist Dr. Rena Malik.

How Long Does Coffee Act As A Diuretic?

The peak diuretic effect of coffee typically occurs within 3 hours of consumption. Caffeine has a half-life in your body of 6 hours. So 6 hours after drinking a cup of coffee, only half of its caffeine content remains in your system. At this point, the diuretic effects are minimal. 

It can take up to 10 hours for caffeine to totally leave your system, however. So you may continue to feel its stimulating effects – something to consider if you struggle with insomnia.

Is Decaf Coffee A Diuretic?

Decaf coffee is not a diuretic. The diuretic effects of coffee stem entirely from its caffeine content. If you’re concerned about dehydration or enjoy sipping cups of coffee all day, consider switching to decaf after the first three or four cups. It’s a good way to limit your intake of caffeine while still enjoying the flavor, comfort, and antioxidant boost of drinking coffee.

Is Tea A Diuretic Like Coffee?

Tea is a diuretic only to the extent that it contains caffeine, just like coffee. Generally, tea has less caffeine per volume than coffee, making it a better hydrator. For example, to get the equivalent caffeine of one 8-ounce brewed cup of coffee, you’d need to drink approximately:

• 12 ounces of matcha
• 16 ounces of black tea
• 20 ounces of oolong tea
• 20 ounces of green tea

So you’ll take in much more liquid than you lose through diuresis. And, of course, there are hundreds of herbal tea flavors with no caffeine at all.

Final Thoughts

Caffeine is a diuretic, but drinking coffee doesn’t dehydrate you as long as you limit your intake to less than five cups per day. If you drink more than that, drinking more water and exercising are good ways to avoid the diuretic effect and dehydration. A better option is switching to decaf coffee or tea before your caffeine levels get too high.