5 Reasons Coffee Can Make You Sleepy 

For many people, a warm, rich cup of coffee is the perfect way to get the day started. In fact, it is the most popular caffeinated beverage in the United States. The caffeine in coffee, about 80 to 100 milligrams per cup, stimulates the nervous system, and provides an energy boost.

However, we all react to caffeine differently. One person may drink several cups of coffee and experience minimal effects. In contrast, another person could drink one cup and experience strong, even negative side effects, such as an elevated heart rate, digestion problems, and a jittery feeling. Coffee can also cause the opposite effect—instead of causing wakefulness, it can cause some people to become sleepy and unfocused.

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If you experience drowsiness after drinking coffee, it may be due to one of the reasons outlined below.

1. Caffeine Blocks Adenosine

Adenosine is a chemical produced in the central nervous system that regulates our sleep schedule. Much like melatonin, the sleep hormone, adenosine levels increase during the day to keep us awake. At night, they decrease to help us fall asleep. Adenosine does this by binding to special receptors in the brain that slow activity and cause relaxation. When you drink coffee, caffeine binds to these receptors and prevents them from receiving adenosine.

However, the body still produces adenosine in the morning even if the receptors are not absorbing it. This causes a build-up of the chemical in the body. Once caffeine is metabolized, the high levels of adenosine can cause extreme fatigue. Since caffeine absorbs quickly, some people may feel these adverse effects 45 minutes after consumption.

2. Coffee is a Diuretic

For those who drink more than four cups of coffee per day, caffeine can act as a diuretic. This means it passes through your body quickly, causing you to use the bathroom more frequently. Over time, water loss can affect your heart’s ability to maintain blood pressure and put you at risk of dehydration. If you do become dehydrated, you may experience daytime sleepiness and lethargy. Dehydration can also lead to rapid heart rate and low blood pressure, which often triggers anxiety. In most cases, drinking a moderate amount of coffee, one to two cups a day, will not cause dehydration. Therefore, be sure to monitor your coffee intake each day.

Although caffeinated beverages, such as coffee, energy drinks, and soft drinks, may force us to use the restroom more often, the water in coffee can counteract dehydration. However, if you drink a lot of coffee, be sure to drink plenty of water throughout the day. According to the USDA water intake recommendations, adult men should have around 13 cups per day, and adult women should have 9 cups.

3. Coffee Sweeteners Affect Blood Glucose Levels

Most coffee creamers have high levels of sugar. Plus, specialty coffee drinks at your local cafe may contain whipped cream, flavored syrup, honey, and chocolate, all of which contain refined sugars that cause what many people describe as a “sugar crash” once metabolized.

A sugar crash happens when you consume too much sugar at once and the body produces insulin to offset it, causing a drastic drop in blood glucose (blood sugar). Blood sugar fuels the body and increases energy, which is one reason people prefer to drink coffee before a workout. This drop in blood sugar levels causes a sleepy, sluggish feeling. A sugar crash can also cause anxiety, mood swings, dizziness, and hunger.

To prevent these effects, try to limit the amount of sugar you add to your coffee and the number of sugary drinks you consume each day. If you develop a sugar crash, you can counteract these effects with a healthy snack, such as nuts, seeds, hard-boiled eggs, or yogurt.

4. Tolerance to Caffeine

Over time, avid coffee drinkers may build-up caffeine tolerance. Caffeine prevents adenosine from binding with receptors. However, to combat this, the body may begin to produce more adenosine receptors. One study found that physically active adults began to experience fewer caffeine effects after 15 days of regular consumption.

However, research on caffeine tolerance is still inconclusive, as other studies suggest regular consumption does not change the rate of absorption or metabolism.

5. Coffee Beans Many Contain Mold

A recent study found that several coffee samples were contained with mycotoxins, such as aflatoxin B1 and ochratoxin A. Although these amounts are below the legal limit and deemed safe for human consumption, other studies have found that mycotoxins can lead to chronic fatigue syndrome.

Frequently Asked Questions

What happens to your body when you stop drinking coffee?

 For those who regularly drink coffee, stopping abruptly can lead to a caffeine withdrawal, which can lead to several uncomfortable side effects, including sleepiness, headaches, nausea, and irritability. 

A gradual decrease in caffeine consumption is a safer alternative. If you want to stop drinking coffee, try decreasing the amount you consume by ¼ cup every two to three days. Eventually, you will decrease your consumption completely and have fewer side effects than if you stopped all at once.

Is caffeine bad for your heart?

Caffeine can raise blood levels and elevate the heart rate. However, research shows these effects are temporary and are not detrimental to your heart health or cholesterol levels.

Those with heart disease and high blood pressure may want to discuss caffeine consumption with their doctor, since high doses of caffeine may be dangerous for these individuals. 

Can coffee help anxiety? 

Since caffeine is a stimulant, it can cause adverse effects for those with anxiety. Caffeine heightens the “fight or flight” response, a physiological reaction to a perceived threat or danger. For those with anxiety, even minor things can trigger this response. The consumption of caffeine can make this reaction even more dangerous and trigger an anxiety attack.

How long does it take for coffee to take effect? 

The body begins to absorb caffeine immediately. Since it passes through the tissue lining the mouth, throat, and stomach so quickly, most individuals feel the effects of coffee fairly quickly, in about 15 to 20 mins.

How many hours before bed should I stop drinking coffee?

Studies show that some individuals may feel the effects of coffee up to 8 hours after consumption. This means your afternoon coffee could cause you to feel active and alert well past your bedtime. Therefore, it is best to avoid caffeinated beverages after 2 p.m. This stretch of time allows your body to metabolize caffeine and keep it from disrupting your sleep.


Coffee is a staple in many people’s lives; however, caffeine is a powerful stimulant, and consumption should be monitored. If you find yourself sleepy after drinking coffee or if you begin to experience any adverse effects, such as dizziness and jitteriness, it is best to reduce your intake. Also, if you suffer from a sleep disorder, such as insomnia, restricting coffee consumption to the morning can help you get a better night’s sleep.

This article is for informational purposes and should not replace advice from your doctor or other medical professional.

Michelle Zhang, Wellness Writer Michelle Zhang

Michelle Zhang is a regular contributor to our Zoma blog and is our go-to sleep researcher. In her time with Zoma, Michelle has researched and published many articles on widespread sleeping habits and troubles. In her time outside of Zoma, Michelle is an occupational therapist and long-distance runner. She believes leading a healthy lifestyle is the key to getting better sleep at night. Michelle's work has been featured on Men's Journal, The Frisky, and The Mighty.

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