Why Coffee Makes You Sleepy? Five Science-Proven Reasons

Woman in bed holding a cup of coffee

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We all know that coffee contains caffeine.

The most widely used stimulant on the planet is caffeine. However, caffeine doesn’t work the same for everyone. Some people can drink several cups of coffee every day and get little benefit from it at all. There are people, however, who prefer taking naps after drinking a cup of coffee. We found out why this happens and how to make coffee invigorating instead of lulling.

Read about the five possible reasons that a cup of coffee makes you sleepy.

Reasons Coffee Makes You Sleepy

1. Coffee relieves fatigue only for a while

It works through unique molecular mechanisms – a blockage of adenosine receptors in the brain. Adenosine is responsible for the sleep-wake cycle. Its amount increases during the day and decreases during sleep.

Adenosine molecules bind to special receptors to prepare the brain for sleep, and brain activity begins to slow down. Caffeine blocks this connection by binding to adenosine receptors. Caffeine is absorbed very quickly; the first effects can be felt after a few minutes, and within 45 minutes absorbs 99% of the caffeine. After the effect of caffeine wears off, it causes a feeling of drowsiness.

2. Coffee can make you pee more

Coffee speeds up metabolism, so it can be helpful for those who like to spend time in the gym. However, the drink has a slight diuretic effect. Therefore, if after a couple of cups, you go in for sports, you may lose more fluid than usual. Because of its lack, people often feel lethargic, tired, and sleepy. Dehydration could make you feel tired. Drink water throughout the day, and eat more fruits and vegetables.

3. Poor coffee quality

A strange smell and too strong bitterness are characteristic signs of low-quality coffee. It may contain toxins that mold releases. Many studies have confirmed that this can cause fatigue and dizziness. Try not to drink cheap (or expired) and questionable-quality coffee. Choose coffee from trusted brands, and do not store any expired product

4. Too much sugar

Sugar is absorbed by the body faster than caffeine. Some people have a sharp drop in glucose levels as early as an hour and a half after drinking sweet coffee. This may result in fatigue. Try to chill out with the sugar packets.

5. Caffeine can cause anxiety.

Many studies confirm that caffeine produces stress hormones – adrenaline and cortisol. If you sleep less than seven hours a night, week after week, after a few cups of espresso, your heart rate and anxiety may increase, causing overwork and drowsiness.


According to meta-analysis (review of a large number of studies), caffeine increases blood sugar levels by decreasing insulin sensitivity. Until blood sugar levels return to normal, people with elevated blood sugar can experience headaches, fatigue, difficulty concentrating, extreme thirst, and frequent urination.

The effects of caffeine on sleep quality have been documented by many researchers and you should definitely check out more of the official caffeine research from the true geniuses at the National Library of Medicine.

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