Six Reasons Coffee Can Make You Sleepy

By Stacy Liman
Last Updated On April 8th, 2020

We know coffee mostly as our wake-up drink. We have one, two, or even three cups, and we’re ready to face our day. And while coffee has many different ingredients,…

Six Reasons Coffee Can Make You Sleepy

We know coffee mostly as our wake-up drink. We have one, two, or even three cups, and we’re ready to face our day. And while coffee has many different ingredients, it’s caffeine that receives the most attention.

Ingesting caffeine stimulates your central nervous system, which wakes you up and feel more energetic. However, what about when coffee doesn’t seem to wake you up and leaves you feeling sleepy instead? Has the caffeine failed you?

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Coffee can affect your body in various ways, and how it affects you is different for everyone. We’ve compiled a list of six reasons why coffee might leave you feeling sleepy.

Coffee Blocks the Effects of Adenosine

When you drink coffee, your stomach and small intestine absorbs the caffeine and redistributes it through your bloodstream to multiple parts of your body, including your brain. After caffeine reaches your brain, it sticks to your adenosine receptors.

Now adenosine helps you feel sleepy and controls your sleep-wake cycle. When caffeine binds to your adenosine receptors, your brain isn’t processing its adenosine, but that doesn’t mean it stops producing it. So once the caffeine wears off, there’s a build-up of adenosine that will bind to your brain’s receptors, making you feel tired.

Coffee is a Diuretic

In simpler terms, drinking a cup of coffee may cause you to use the bathroom more often. If you drink a moderate amount of coffee (two to three cups), you may not notice anything, but if you drink four or more cups of coffee, you may find yourself running to use the restroom.

If you lose more fluids than you’re drinking, you may feel tired as dehydration takes effect. Other symptoms of dehydration include thirst, dry mouth, dizziness, dry skin, and a lack of sweat.

However, coffee may not actually dehydrate you that much. As Harvard Medical explains, while caffeinated beverages may increase restroom visits, the water in the drink still contributes to your overall fluid consumption.

To counteract dehydration, drink plenty of water and eat foods that contain water, such as fruits and vegetables. When you’re exercising, sick, or experiencing hot, humid, or cold weather, you may need to drink more water than usual. If your dehydration symptoms include fainting, a sped-up heart rate, rapid breathing, confusion, or shock, seek immediate medical attention.

It’s the Sweetener, Not the Coffee

If you drink coffee sweetened with whipped cream, honey, syrup, or plain old sugar, you might feel tired if a sugar crash hits you.

When your body ingests more sugar than it’s used to, insulin is produced to offset it. However, the insulin also causes your blood glucose levels to drop—and your blood glucose, also known as your blood sugar, is your body’s main source of energy.

So as your blood glucose levels decrease, you feel a lack of energy that can tire you out. You may also feel hungry, irritable, anxious, sweaty, dizzy, or on edge as the sugar crash hits.

It may not just be the sugar in your coffee, either. If you have a sweet snack such as a cookie or drink your morning coffee with a glass of orange juice (which can have as much sugar as five or six oranges), you might feel a sugar rush and subsequent decline. It’s particularly easy to binge sugary drinks, as they don’t fill you up the way food does.

If you experience a sugar crash, try having some protein to balance out your blood sugar levels.

It’s the Mold, Not the Coffee

It’s gross to think about, but the reason you might grow tired after a cup of coffee is from mold contamination. A 2003 study examined 60 samples of raw, unroasted coffee beans (known as green coffee) from Brazil.

“Practically all samples (91.7%) were contaminated with moulds (sic),” the study noted.

2017 study also examined coffee samples for mycotoxins, a product of microfungi. Mycotoxins found in the samples included aflatoxin B1 and ochratoxin A; however, the concentrations of mycotoxins were deemed “acceptable according to legal limits.”

And a 2013 study has linked exposure to mycotoxins to chronic fatigue. Those with chronic fatigue feel tired even after resting and may experience sleep problems. Other symptoms include dizziness and difficulty thinking or concentrating.

Caffeine Affects Stress

Stress can keep you awake at night, as anyone with stress-induced insomnia knows. However, stress can leave you feeling tired or fatigued during the day. If you’re feeling stressed, you may want to sleep to process the experience, as you consolidate emotional memories during sleep.

We feel stressed in reaction to the stress hormone cortisol, which signals our body to stay on high alert in response to a perceived stressor. Another component of our bodies’ stress response is epinephrine, commonly known as adrenaline. As epinephrine travels throughout the body, the heart speeds up and we breathe faster to increase our alertness.

Now, a 2017 study found that ingesting caffeine doubled the levels of epinephrine and cortisol, regardless of whether the subject regularly consumed caffeine or not. This means you can feel stressed after drinking coffee, even if it’s the same amount you drink every day. And your body might translate that stress into sleepiness, once the initial stress response has passed.

Caffeine Withdrawal Symptoms

caffeine withdrawal
If you regularly consume coffee and then stop abruptly, you’re likely to feel the effects of caffeine withdrawal. Sleepiness is one symptom of caffeine withdrawal, along with headaches, nausea, irritability, and an inability to concentrate. You can feel withdrawal set in within 12 to 24 hours after you last ingested caffeine. Depending on how much caffeine you regularly consumed, symptoms may last only a few days or a couple of weeks.

If you want to quit drinking coffee and avoid caffeine withdrawal symptoms, try a gradual approach. Cut back on your consumption by ¼ of a cup every two to three days, or switch to green tea for less caffeine. Continue cutting back until you’re no longer consuming caffeine.

Frequently Asked Questions

How long does it take for coffee to take effect?

You’re likely to feel the caffeine kick in as little as 10 minutes, and the amount of caffeine circulating in your blood peaks within 30 to 90 minutes after consumption. While you may stop feeling the effects within a few hours as the caffeine is metabolized, it takes many hours for caffeine to completely leave your body.

Can caffeine not affect you?

If you regularly consume caffeine, you may stop noticing the effects of your usual cup of coffee as you develop a tolerance.

Is caffeine bad for your heart?

Numerous studies have examined the link between caffeine, coffee, and coronary heart disease, but results vary. Outside factors such as other dietary choices may have affected the results. The American Heart Association says that drinking one or two cups of coffee a day should be all right.

A 2017 review noted caffeine “is more often associated with benefit than harm for a range of health outcomes across multiple measures of exposure, including high versus low, any versus none, and one extra cup a day.”

How does caffeine affect your sleep?

Caffeine close to bedtime can keep you from getting a good night’s sleep. If you ingest caffeine six hours before bed, you may still feel the effects when you turn in for the night. The half-life of caffeine, or the time it takes for your body to get rid of half the caffeine you ingest, varies from three to seven hours in adults.

How do you flush out caffeine?

Drinking more water, exercising, and eating are all common recommendations for a mild caffeine overdose. Drinking herbal tea and practicing breathing exercises may also help you feel calmer.

Did We Help?

Coffee contains stimulating caffeine, but it has its limits. You might feel tired as you feel the effects of adenosine build-up, dehydration, decreased blood sugar, and more. The reasons you feel sleepy can vary, but the solution might be getting a better night’s sleep.

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

About the author

Stacy Liman is a journalism graduate student and a freelance writer with a focus on mindfulness and content marketing. Stacy enjoys discovering new mattresses and connecting people with their perfect bed, but she more so enjoys understanding and writing about the science of sleep to help people get deeper, healthier rest.

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