How Caffeine Works, and What it Means for Sleep

Medically reviewed by
 Brittany Ford, RHN

Brittany Ford, RHN

Brittany Ford is a Registered Holistic Nutritionist with multiple years of expertise. Since becoming registered in 2019, Brittany has committed herself to helping individuals achieve optimal well-being through a holistic…

Last Updated On December 7th, 2023
How Caffeine Works, and What it Means for Sleep

Key Takeaways

Caffeine’s Dual Nature: Caffeine such as coffee and energy drinks serve as a powerful stimulant that provides energy and focus, making it valuable for busy individuals. However, excessive consumption can exacerbate sleep problems, both by keeping people awake at night and causing restlessness during the day.

How Caffeine Works: Caffeine functions by altering brain chemistry. When feeling sleepy, the brain naturally produces adenosine, a chemical linked to sleep. Caffeine, structurally similar to adenosine, binds to receptors in the brain, preventing them from detecting adenosine. This leads to increased neuron activity, triggering the production of adrenaline and resulting in heightened alertness.

Caffeine’s Effects and Caution: Beyond its wakefulness-inducing properties, caffeine has additional benefits such as boosting metabolism, enhancing cognitive function, and improving mood. However, excessive caffeine intake (more than 400 mg per day) can lead to adverse effects like shakiness, increased heart rate, and dehydration. Additionally, caffeine’s half-life of six hours means it can disrupt sleep for some individuals, emphasizing the importance of moderating intake, particularly in the hours leading up to bedtime.

For the busy and overworked among us (basically, everyone) caffeine might be the ultimate double-edged sword. It’s a no-fail stimulant that gives us the energy and focus we need to plow through our crazy, hectic days—even when we’re running low on shuteye.

But take in too much of the stuff, and it can end up making your lack-of-sleep problems even worse. Caffeine is notorious for keeping people awake at night, which over time can mess with your body’s internal sleep clock. And even during the day, consuming too much can leave you feeling restless and jittery.

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How exactly does the all-powerful stimulant work, and what does it mean for your sleep? Let’s find out.

What is Caffeine?

OK, a quick review of the basics: Caffeine is a stimulant that exerts an energizing effect on the central nervous system. Verified Source National Library of Medicine (NIH) World’s largest medical library, making biomedical data and information more accessible. View source It occurs naturally in coffee beans, but is also present in cocoa beans and other plants like tea leaves, kola nuts, guarana, and yerba mate.

Typically, caffeine’s boost hits about 15 minutes after consuming the stuff. And, for better or worse, it’ll stay in your system for about six hours. Read more about How Long Does It Take for Caffeine to Wear Off for Sleep.

How Caffeine Works to Wake You Up

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We all know that glorious feeling. Start sipping a cup of coffee when you first wake up or when you’re exhausted in the afternoon, and almost immediately, you start feeling an energized and alert caffeine kick.

What’s happening on the inside? Caffeine is a stimulant that actually alters your brain chemistry Verified Source National Library of Medicine (NIH) World’s largest medical library, making biomedical data and information more accessible. View source in a way that blocks your brain from feeling tired.

Here’s how: When you’re feeling sleepy, your brain is normally producing adenosine, Verified Source National Library of Medicine (NIH) World’s largest medical library, making biomedical data and information more accessible. View source a natural chemical that’s associated with sleep. To the receptors in your brain, caffeine looks really similar to adenosine. Thanks to that similarity, caffeine can bind to those receptors, making them unable to pick up any adenosine.

Once your brain receptors can’t sense any adenosine because they’re filled up with caffeine, your neurons start firing at rapid speed. The spike in activity makes your pituitary gland think that you’re having an all-out emergency, so it tells your body to produce adrenaline. Verified Source Cleveland Clinic Ranked #2 hospital by U.S. News & World Report and one of the largest academic medical centers in America. The Cleveland Clinic serves patients from all over the world. View source

The result? You end up in fight-or-flight mode: Your pupils dilate, your heart rate speeds up, and your liver sends sugar into your bloodstream for extra energy. Oh, and you feel really awake!

“In a nutshell, caffeine, a neuroactive compound, disrupts the adenosine receptor system, triggering heightened neuronal activity and the release of adrenaline,” says Brittany Ford, RHN. “This orchestrated interplay induces a state of heightened alertness, revealing the intricate neurobiology behind the familiar caffeine-induced wakefulness we experience. ”

Other Benefits of Caffeine

Caffeine’s effect on your energy level is pretty miraculous in itself—but the stuff can do more than just perk you up. Research shows that caffeine can also…

  • Fire up your metabolism. As little as 50mg of caffeine can jump-start your body’s resting energy expenditure, found a 2009 study. Verified Source National Library of Medicine (NIH) World’s largest medical library, making biomedical data and information more accessible. View source Translation: It helps you burn more calories without lifting anything but your coffee cup.
  • Boost your brainpower. Caffeine relaxes your blood vessels, which means the more you consume, the more blood flows into your brain. And when more blood flows into your brain, you focus better, plus have an easier time making decisions and solving problems.
  • Help you feel happy and relaxed. Just 100mg of caffeine—about the amount in a cup of coffee—has been shown to enhance your mood and reduce anxiety. Verified Source National Library of Medicine (NIH) World’s largest medical library, making biomedical data and information more accessible. View source Nice. 

“Caffeine, a natural stimulant, not only provides a quick pick-me-up but also exhibits a range of cognitive and physiological benefits,” says Ford. “Research suggests that moderate caffeine intake can enhance alertness, improve mood, and boost cognitive functions such as attention, memory, and reaction time.”

“Furthermore, caffeine has been associated with potential long-term benefits, including a reduced risk of certain neurodegenerative diseases. It’s a versatile compound that, when consumed in moderation, can be a valuable ally in promoting mental acuity and overall well-being.”

The Dark Side of Caffeine


For most people, 400 mg caffeine (the amount in two to four cups of coffee) per day is totally fine. But consuming more than that could pose problems. Some signs that you may have had too much caffeine:

  • Feeling shaky or jittery
  • Headaches or dizziness
  • Increased or abnormal heart rate
  • Dehydration
  • Upset stomach

What’s more, caffeine is a drug, which means that your body becomes addicted to its effects. Miss your dose or cut back too quickly, and you’re suddenly in the throes of withdrawal. Which, as anyone who’s ever missed out on their regular morning coffee can tell you, feels like pure torture.

Worst of all, though, is the way that caffeine can wreck your sleep. More on that below.

How Caffeine Affects Your Sleep

Caffeine and sleep is different for everyone. Some people can consume caffeine an hour before bed and have zero trouble nodding off. Others might sip a cup of coffee at three o’clock in the afternoon and end up tossing and turning all night. Why?

Caffeine has a half-life of six hours, which means it takes about that long for the stuff to leave your system after caffeine consumption. Still, that’s an average. In reality, everyone’s bodies metabolize caffeine at a different rate, which means that it’ll give some people more sleep trouble than others.

If you find that you’re sensitive to the effects of caffeine, it’s a good idea to cut off the coffee and caffeinated tea by mid- to late-afternoon. In fact, avoiding caffeine for a full six hours before bed could help you get an extra hour of sleep, found one study published in the Journal of Clinical Sleep Medicine. Verified Source National Library of Medicine (NIH) World’s largest medical library, making biomedical data and information more accessible. View source

But remember, caffeine isn’t just in coffee or tea. If you’ve cut those things out and are still having trouble sleeping, consider whether you’re unknowingly taking in caffeine from other sources. (Believe it or not, the FDA doesn’t require manufacturers to list caffeine content on a food or beverage’s label.) In addition to coffee and tea, caffeine also lurks in:

  • Energy drinks Seems obvious, but not always. Even some enhanced waters, like Vitamin Water, can come in “energizing” flavors that are loaded with caffeine.
  • Decaf coffee The name isn’t exactly accurate, since a test found that an 8-ounce serving of most decafs contain roughly 2 mg of caffeine. Verified Source Mayo Clinic Ranked #1 hospital by U.S. News & World Report and one of the most trusted medical institutions in the world. The staff is committed to integrated patient care, education, and research. View source
  • Soda Not just Coke and Pepsi, though. Mountain Dew, root beer, orange soda, and cream soda all contain caffeine, too.
  • Chocolate Milk chocolate doesn’t have much, but if you consume caffeine in the form of a serving of the dark stuff can contain 30mg of caffeine. Skip it as a late-night snack in favor of walnuts or pumpkin seeds, which actually help you sleep better.
  • Pain relievers Caffeine can ease headaches, which is why the stimulant is often added to pain pills.
  • Chocolate or coffee-flavored stuff Obviously, numbers vary widely. But any food or drink with caffeine-containing ingredients—like devil’s food cake or coffee ice cream—will also contain caffeine.

“Caffeine, by blocking adenosine receptors, can impact sleep onset and quality,” says Ford. “While moderate consumption earlier in the day may not disrupt sleep for everyone, awareness of individual sensitivity and circadian rhythms is crucial for maintaining a balance between wakefulness and restorative sleep.”

Finding the Right Balance

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Photo by Flickr user martin_heigan

In moderation, caffeine isn’t harmful—and could even be helpful. That said, moderation means different things for different people. Just like some people need less sleep than you think, other people may need to consume less caffeine to snooze well.

If you’re having trouble sleeping, try gradually cutting back on all sources of caffeine and avoid the stuff in the hours leading up to bedtime. Steer clear of going cold turkey (it’ll only leave you feeling worse), and try reducing your caffeine content over the course of a week or so.

Hopefully, that does the trick. But if not, don’t panic! Moderating your caffeine intake is just one way to up your chances for getting a better night’s rest. Here are some other tips and tricks on how to sleep better that can really have a positive impact on your health.

Do you drink caffeine in the afternoon? Does caffeine affect how well you sleep? Has cutting back on caffeine helped you sleep better?

About the author

Marygrace Taylor is an award-winning health writer for Amerisleep. Her commitment to sleep health is evident in her ability to consistently prioritize eight hours of sleep each night. Her in-depth interviews with industry experts, such as Ken Ceder on "Why Light is Essential for Great Sleep and Optimum Health," highlight her dedication to delivering valuable insights. Marygrace's work has been featured in reputable publications like Business Insider, Glamour, Refinery29, Metro UK, and Hunker, further solidifying her expertise in the field.

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