Written by Ryan Raman, MS, RD on December 11, 2019 — Medically reviewed by Katherine Marengo LDN, R.D.
Coffee is one of the most popular beverages in the world.
A major reason why people drink coffee is for its caffeine, a psychoactive substance that helps you stay alert and aids performance.
However, caffeine can be dehydrating, which may make you wonder whether drinking coffee hydrates or dehydrates you.
This article tells you whether coffee is dehydrating.
A key reason why people drink coffee is to get their daily dose of caffeine.
Caffeine is the most consumed psychoactive substance in the world. It may help boost your mood and elevate your mental and physical performance (1Trusted Source).
Inside your body, caffeine passes through the gut and into the bloodstream. Eventually, it reaches your liver, where it’s broken down into several compounds that affect how organs like your brain function (2Trusted Source).
Though caffeine is mainly known for its effects on the brain, research has shown that it may have a diuretic effect on the kidneys — especially in high doses (3Trusted Source).
Diuretics are substances that cause your body to make more urine than usual. Caffeine may do so by increasing blood flow to your kidneys, which spurs them to release more water through urine (4Trusted Source).
By encouraging urination, compounds with diuretic properties like caffeine may affect your hydration status (3Trusted Source).
Coffee is high in caffeine, a substance that may have diuretic properties. This means that it may cause you to urinate more frequently, which may affect your hydration status.
Different types of coffee contain different amounts of caffeine.
As a result, they may affect your hydration status differently.
Brewed or drip coffee is the most popular type in the United States.
It’s made by pouring hot or boiling water over ground coffee beans and is typically done using a filter, French press, or percolator.
Instant coffee is made from brewed coffee beans that are freeze- or spray-dried.
It’s simple to prepare, as all you need to do is mix 1–2 teaspoons of instant coffee with hot water. This allows the coffee pieces to dissolve.
Instant coffee has less caffeine than regular coffee, with 30–90 mg per 8-ounce (240-ml) cup (7Trusted Source).
Espresso coffee is made by forcing a small amount of very hot water, or steam, through finely ground coffee beans.
While it’s smaller in volume than regular coffee, it’s high in caffeine.
One shot (1–1.75 ounces or 30–50 ml) of espresso packs around 63 mg of caffeine (8Trusted Source).
Decaf is short for decaffeinated coffee.
It’s made from coffee beans that have had at least 97% of their caffeine removed (9Trusted Source).
On average, an 8-ounce (240-ml) cup of brewed coffee contains 95 mg of caffeine, compared with 30–90 mg for instant coffee, 3 mg for decaf, or 63 mg for a shot (1–1.75 ounces or 30–50 ml) of espresso.
Though the caffeine in coffee may have a diuretic effect, it’s unlikely to dehydrate you.
For caffeine to have a significant diuretic effect, studies show that you need to consume more than 500 mg per day — or the equivalent of 5 cups (40 ounces or 1.2 liters) of brewed coffee (12Trusted Source, 13Trusted Source, 14Trusted Source).
A study in 10 casual coffee drinkers reviewed the impact of drinking 6.8 ounces (200 ml) of water, lower caffeine coffee (269 mg of caffeine), and high caffeine coffee (537 mg of caffeine) on signs of dehydration.
Researchers observed that drinking the higher caffeine coffee had a short-term diuretic effect, whereas the lower caffeine coffee and water were both hydrating (15Trusted Source).
For example, a study in 50 heavy coffee drinkers noted that drinking 26.5 ounces (800 ml) of coffee daily for 3 days was equally as hydrating as drinking the same amount of water (16Trusted Source).
Also, an analysis of 16 studies discovered that taking 300 mg of caffeine in a single sitting — equivalent to 3 cups (710 ml) of brewed coffee — increased urine production by only 3.7 ounces (109 ml), compared with drinking the same amount of non-caffeinated beverages (17Trusted Source).
So, even when coffee makes you urinate more, it shouldn’t dehydrate you — as you don’t lose as much fluid as you originally drank.
Drinking moderate amounts of coffee shouldn’t dehydrate you. However, drinking large amounts of coffee — such as 5 or more cups at once — may have a minor dehydrating effect.
Coffee contains caffeine, a diuretic compound that can increase urination frequency.
That said, it takes drinking large amounts, such as 5 cups of brewed coffee or more at once, for it to have a significant dehydrating effect.
Instead, drinking a cup of coffee here or there is hydrating and can help you reach your daily fluid needs.