Most Americans simply cannot get enough coffee. According to the National Coffee Association, nearly two-thirds of the country has at least one cup of joe each day. The reason is simple: coffee provides a caffeinated boost to keep you going.

But not everyone gets wired with energy when the caffeine hits. You may be asking “why does caffeine make me sleepy? There’s an explanation. But you may want to rephrase your question, instead of asking “why coffee makes me tired?”, you’d rather inquire about how caffeine affects your body.

Reason 1: Coffee Blocks Adenosine

Your body naturally produces a chemical called adenosine, a neurotransmitter responsible for causing fatigue. When you drink coffee, caffeine enters your bloodstream and is distributed throughout your body, including to your brain. Once it reaches your brain, caffeine sticks to your adenosine receptors and blocks you from receiving that chemical. However, your body continues to produce it. That means when you inevitably come down from your caffeine rush, your brain is bombarded with all the built-up adenosine. The result? You end up feeling tired, groggy, and like you need to reach for another cup of coffee!

Reason 2: Coffee Makes You Pee

You probably know that coffee is a natural laxative, but you may not have been aware that it’s also a diuretic. That means that coffee also makes you need to pee a lot. Studies have shown that if you are a moderate to heavy coffee drinker, consuming four cups per day or more, you might find yourself heading to the bathroom more often than usual.

When you pee, you remove fluids from your body. That process can lead to you becoming dehydrated. Just how dehydrated coffee makes you is up for debate, as it does provide your body with some water. But by emptying your bladder more often, you run the risk of suffering from the effects of dehydration, which can include feeling sleepy. This occurs because the lack of fluid in your blood slows down circulation and increases your heart rate, which can make you sluggish or tired.

Counter this by staying hydrated. Drink water throughout the day, consume water-dense foods like fruits and vegetables and lay off the coffee if you start to feel dizzy or experiencing dry mouth or skin.

Reason 3: You’re Drinking The Cheap Stuff

It’s widely accepted that you get what you pay for, and coffee is no exception to that rule. If you’re buying bottom-shelf coffee at your local supermarket, there’s a chance you’re buying a blend of sub-par coffee from Vietnam or Brazil, and “sub-par” is putting it lightly. After a study was done by the Department of Public Hygiene in Lisbon, Portugol, they concluded that 91.7% of Brazilian coffee tested positive for mold (yuck!).

Further studies have linked exposure to mycotoxins, the toxic chemical products created by fungi, to chronic fatigue in humans.

So naturally, your body is going to react negatively to the moldy coffee, leaving you feeling tired and foggy-headed. To avoid this, spend a few extra bucks to ensure you’re buying coffee from reputable brands or farms.

Reason 4: Too Much Sugar In Your Coffee

Most of us enjoy a good peppermint mocha from Starbucks around the holidays, a cold java chip frappuccino for the summertime. These are certainly tasty drinks, but they’re also absolutely loaded with sugar. You could even argue that you’re drinking a cup of sugar with a splash of coffee. And if that’s the case, a sugar crash could be the reason for your grogginess.
Sugar is processed by your body much quicker than caffeine. Some people experience sugar crashes at little as 90 minutes after consuming the sweetener. Once it makes its way through your system, it’s possible you may experience fatigue in the aftermath.

coffee drink sleep sugar
Although delicious, specialty coffee drinks often contain a ton of sugar

Reason 5: Caffeine Causes Stress

Stress can wreak havoc on your body. Unfortunately, caffeine can contribute to those feelings. When you’re in stress, your body releases the hormone cortisol, which tells your body to remain on high alert (stressing you out even more). Epinephrine, otherwise known as adrenaline, can have a similar effect, rushing through your body and increasing your heart rate.

According to scientific research, consuming caffeine can double the levels of both epinephrine and cortisol. This can happen to even regular coffee drinkers, causing spikes in stress. Putting your body in that high-alert state can tire you out and make you feel sleepy.

How To Minimize These Effects

If you find yourself sleepy after a cup of coffee, there are a few things you can do to try and prevent it.

First things first, start with some general best practices for your health. Try to get at least 7-8 hours of sleep per night in a comfortable bed. This can reduce stress, helps you think clearly, and makes it easier to focus. All of this will reduce your reliance on caffeine to keep you going.

Secondly, even if you need a caffeine boost during the day or simply enjoy the routine of a cup of coffee, try not to overdo it. The Mayo Clinic recommends folks consume no more than 4 eight-ounce cups per day.

Finally, don’t forget to stay hydrated. Make sure you’re drinking enough water along with your coffee to prevent dehydration. The Institute of Medicine recommends men get 13 cups of fluids per day and women get 9 cups per day. That includes water consumed from food, but most of your hydration will come from drinking water.

Final Thoughts

If you ask yourself “how come coffee makes me sleepy?”, remember that it isn’t the caffeine itself, but rather how it affects your body. Not getting enough rest or drinking enough water? Caffeine is just going to make matters worse. Take care of your body first and you might be able to make the most of your daily cup of joe. Otherwise, that coffee may make you feel tired because your body has other needs that caffeine can’t fix.


Why do I get sleepy after drinking coffee?

You get sleepy after drinking coffee because of how caffeine affects your body. It may be causing you stress or dehydrating you, which can lead to feeling tired. If you drink cheap coffee, it could contain mold that causes fatigue. While sugary coffee drinks can cause a sugar crash.

Is it bad to have coffee every day?

In moderation, coffee is not likely to be bad for you. Keep your consumption under 4 eight-ounce cups per day and you should be safe. Going over that amount could have negative effects to your body and health.

How does caffeine affect your sleep?

Caffeine can affect your sleep. Caffeine has a half-life of between three to seven hours in adults, meaning it remains in your body for that long and can continue to affect you. Try not to drink coffee or other caffeinated beverages within six hours of when you’re planning to go to sleep.

How long does it take for coffee to affect me?

It can take caffeine as little as 10 minutes to affect you, though you’ll likely feel the peak of it within 30 to 90 minutes of consuming it. Those effects can wear off within a few hours, and if you’ve built up a tolerance, you may be largely unaffected by caffeine.