Why Does Coffee Make Me Sleepy?

Updated: Jun. 04, 2021

Drinking coffee may make some people feel tired or sleepy, but coffee itself isn't the culprit. Here's how the drink affects your body and what may be behind your coffee-related tiredness.

The relationship between coffee and energy

If you’re a coffee drinker, there’s a good chance that you lean on your morning cup to wake up. You may grab an iced Americano or a creamy blended Frappuccino to power through the afternoon at work.

In the evening, you might even reach for a decaf coffee with dessert after dinner.

Sound familiar? You’re not alone. About 58 percent of Americans drink coffee for morning energy, according to a recent report by Statista, a market research company. The average drinker also downs three cups per day, according to the National Coffee Association’s 2020 National Coffee Data Trends Report.

Clearly the caffeine in a cup of joe is used to combat tiredness and deliver a boost of energy. So why do some people claim that coffee makes them sleepy? Here’s everything you need to know about why coffee might make you feel tired and how to maximize its energizing effects.

Caffeine may interfere with your sleep-wake cycle

The caffeine in your coffee is a natural stimulant. It works by interfering with adenosine, a naturally occurring chemical that builds up through the day until it triggers sleepiness at night. As you sleep, levels drop again, only to start the cycle all over the next day.

“Caffeine molecules block [adenosine’s] receptor sites, providing the temporary perception we are not as tired or sleep-deprived as we may be,” says Dr. Greene. “At a certain point, the adenosine volume will supersede caffeine’s effects, and we will most certainly have to sleep.”

In other words, drinking too much caffeine could simply mean you’ll crash harder later.

This can lead to a vicious “coffee cycle,” in which you guzzle coffee to stay awake, stay up later thanks to the caffeine, and wake exhausted when your alarm goes off bright and early the next morning. And repeat.

In a 2018 study published in Risk Management and Healthcare Policy, the researchers discuss this cycle, stating, “Researchers have commonly found that feeling tired in the morning leads to high caffeine use, which in turn is associated with impaired subsequent sleep patterns.”

You may have built up a tolerance

If your morning coffee isn’t giving you the jolt you’re used to, you may have built up a tolerance to caffeine.

This doesn’t take long—only a matter of days—but can make it feel like your daily brew isn’t doing its job. As a result, you’ll feel tired.

This doesn’t mean the coffee is directly causing sleepiness. Instead, you need more caffeine to feel the same energy. The good news is there are steps you can take to avoid or overcome a caffeine tolerance.

Coffee may relax you

On its own, a single cup of coffee is unlikely to send you to dreamland. But it’s possible the ritual of drinking something warm—whether that’s coffee, tea, or milk—may relax and comfort you.

Ryan Greene, an osteopathic doctor specializing in human performance, sports medicine, and nutrition in Santa Monica, California, says it’s plausible that a person may mentally link coffee consumption with relaxation, though he hasn’t had any patients who approach coffee this way.

Consider how decaf coffee can help people unwind—say, after a big dinner.

“Some will [drink] decaffeinated coffee in the evening as a habitual activity to signal the beginning of their winding down from the day,” says Dr. Greene.

Your coffee may have too much sugar

Is your perfect cup of coffee a caramel-drizzled mocha topped with whipped cream and chocolate shavings? You may be able to blame your exhaustion on the sugar, not the coffee.

A meta-analysis of 31 studies published in 2019 in Neuroscience & Biobehavioral Reviews found that eating sugary snacks can cause fatigue in less than an hour. That is, you’re giving yourself a sugar crash—not a sugar rush. In fact, the sugar rush is a myth, according to the team, led by researchers from Humboldt University of Berlin, Germany.

“The large sugar load consumed—and subsequent insulin response and hypoglycemia, or ‘crash’—can then prompt an individual to seek another quick burst of caffeine or sugar to counteract,” says Dr. Greene. Then the cycle starts all over again.

You may be dehydrated

Fatigue is just one sign of dehydration. Since coffee is a diuretic, which means it makes you pee, it might be possible to drink so much coffee and pee so much that you become dehydrated.

But Dr. Greene says that’s an extreme and unlikely scenario. “More often than not, other factors contribute to the general lethargy,” he says.

The truth is that coffee is not as dehydrating as many people think. It still contains water, which means that it can still count toward your daily liquid consumption. That said, if you are dehydrated, it’s best to reach for a glass of water instead of a cup of coffee.

Dairy may play a role

Warm milk has long been touted as a drink that helps you sleep. That’s mostly due to comfort and ritual, but there’s a small chance it could be traced to milk’s tryptophan content. That’s the amino acid that gives turkey its reputation for inducing sleep.

“Tryptophan [is] known to contribute to drowsiness and subsequent sleepiness,” Dr. Greene says. Still, he cautions against blaming your fatigue on the cream in your coffee.

Milk has such a small percentage of tryptophan that it would be unlikely to cause noticeable sleepiness, he says. Unless you’re drinking a little coffee with your cream, there’s probably another factor at play.

How to drink coffee without getting sleepy

A 2018 study in Nutrients suggests that your sensitivity to caffeine is genetic. That means that the same java that gives you a mild energy boost might give someone else the jitters.

Regardless of your personal tolerance for caffeine, there are ways to maximize coffee’s energizing capabilities while minimizing side effects including exhaustion.

  • Drink fewer cups to break out of the “coffee cycle.” Dr. Greene recommends sticking to 50 to 100 mg of caffeine (one to two cups of black coffee) per day.
  • Wean yourself off of sugar or flavored syrups. This could help you avoid a sugar crash.
  • Experiment with plant-based milk to determine if dairy might be triggering fatigue.
  • If you enjoy coffee for the ritual rather than the energy jolt, consider drinking decaffeinated java or even tea.

A “coffee nap” may make you less tired

While it might seem counterintuitive, you can drink coffee just before a short nap—and before caffeine kicks in—to reduce sleepiness overall.

In a study published in the journal Psychophysiology, 12 cab drivers combined a short 15-minute rest period with either 200 mg of caffeine or a placebo.

While the caffeine helped increase alertness and reduce incidents during an afternoon drive, the combination of caffeine, followed by a short nap, resulted in greater alertness than a nap or caffeine alone. (The naps seemed to work even if the drivers only achieved “nonsleep dozing.”)

Other studies have also supported the idea that caffeine is more effective at combatting afternoon sleepiness when combined with a nap. It seems even a brief amount of sleep can lower your body’s adenosine, which means there will be less adenosine for the caffeine to deal with when it kicks in.

Next, read about the benefits of turmeric coffee.