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Why does coffee make me sleepy? How caffeine can leave you feeling tired

What to do when coffee has the opposite effect

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Man who is tired
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Coffee is the most popular stimulant in the U.S., consumed by nearly 75% of Americans. As a long-time coffee drinker, there’s no doubt that it’s my favorite stimulant (even if its effects are unnoticeable due to my crazy high caffeine tolerance). Even though I crave coffee’s taste, with a slight bitterness and light sweetness, based on taste alone, I sometimes reach for coffee simply for a major boost of energy from its caffeine content.

At times, I feel perkier after a cup of coffee, but there are also times I’m struggling to stay awake. This phenomenon has left me questioning,” Why does coffee make me sleepy?” If you’ve felt that random wave of tiredness hit you after consuming caffeine, you might have asked yourself this question, too. The question of how coffee and tiredness are interrelated can get confusing, especially given coffee’s well-known reputation as a drink that keeps you awake. Here are a few reasons you might feel tired after drinking coffee.

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Why does coffee make me sleepy?

person drinking coffee
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Regular coffee drinkers may experience the opposite of their desired effect after drinking coffee, leaving them more tired and sluggish than before their last cup. Sleepiness after drinking coffee doesn’t affect everyone; it may only affect you sometimes or not all. People who drink coffee regularly may also notice tiredness after coffee more than those who drink coffee occasionally. Here’s why.

Effects on adenosine receptors

You may feel sleepy after drinking coffee because caffeine blocks adenosine receptors in the brain. Adenosine is an important brain chemical that impacts our sleep-wake cycles. Typically, adenosine levels will increase throughout the day and decrease during sleep, as molecules will bind to receptors in the brain to prepare the body to go to sleep. However, drinking coffee can interfere with this natural process and prevent adenosine from binding to the appropriate brain receptors.

Although you might feel fine immediately after drinking coffee, Adenosine receptors will begin to bind again as the caffeine wears off. Thus, you may feel a wave of tiredness rush in —  leaving you ready for a mid-day nap.

Caffeine tolerance

Caffeine tolerance frequently affects regular coffee drinkers as the body adapts to regular caffeine intake. As tolerance develops, the body will require more and more caffeine to feel those “stimulant” effects. The concept of “caffeine tolerance” is so real that some regular coffee drinkers wonder if there is even any caffeine in their cups. Studies have shown that the brain adapts over time to regular caffeine exposure. This means a person who drinks caffeine daily will produce more adenosine receptors, binding more adenosine and reducing the “stimulant” feelings from drinking coffee. I know “caffeine tolerance” all too well, which could be my sign to give matcha a chance instead.

Blood sugar levels

Most of us have felt an actual blood sugar crash at one point or another, especially after consuming a heavy meal (think post-Thanksgiving dinner). However, caffeine may also impact your glucose metabolism and blood sugar levels. In one study, researchers found that consuming 100mg of caffeine hurt glucose metabolism. While consuming coffee might not affect every person’s blood sugar levels, those with metabolic issues or Diabetes may find coffee makes them more tired.

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Another component of why coffee may make you tired could be what you’re putting in your coffee. Many coffee drinkers have a heavy hand when adding sugar to their coffee or maybe consuming pre-packaged coffees that contain sugar. Hidden sugars in your coffee can impact blood sugar levels, leaving you feeling more tired after finishing your cup. Switching to sugar-free coffees, such as by adding zero-sugar coffee syrups, can help support healthier blood sugar levels.

The coffee sleep cycle

man sleeping
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Caffeine’s effects on adenosine receptors, a build-up of caffeine tolerance, and changes in blood sugars all contribute to why coffee makes us sleepy. However, perhaps one of the more obvious reasons for sleepiness from coffee is due to the never-ending “coffee sleep cycle.” Picture this — you’re tired from a stormy night of sleep, and you wake up and rush to consume two cups of coffee. Then noontime hits, and you feel sluggish again, consuming another cup of coffee. You make it to 3:30 p.m., where you consume one last cup of coffee (or two) to finish the work day. Before you know it, you’ve lost track of the number of cups you’ve had that day.
Sipping on all of this caffeine ultimately affects your sleep quality and cycle when it comes time to get to sleep that day. Studies show that caffeine can greatly impact a normal sleep cycle, making falling and staying asleep difficult. This contributes to a poor night of sleep, leaving you with more daytime sleepiness the following day. Then, the cycle continues as you reach for another cup of coffee to make it through the next day. While this phenomenon may not leave you tired immediately after drinking a cup of coffee, it’s a never-ending cycle that contributes to feeling tired, day after day.
Emily Caldwell
Emily Caldwell
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Emily is a freelance journalist with a focus on food, travel, health, and fitness content. She loves to travel to new…
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