Feeling sleepy after coffee? Learn how caffeine can make you tired

If you have ever found yourself astounded that you feel a little drowsy after your daily coffee, you’re not alone. While many of us drink coffee because of its excellent flavor and aroma, we also tend to rely on it for our daily jolt of energy as well.

That’s why it can be so confusing to feel sluggish and sleepy after coffee, rather than energized and alert.

What we have to remember is that one of the main ingredients in coffee is essentially a legal drug: caffeine. While I sympathize with those who prefer not to think of coffee as a vessel for delivering a drug into our bodies, that is exactly how caffeine reacts.

In order to understand the “sleepy after coffee” phenomenon, let’s explore what we know about coffee. 

What's in Coffee Beans?

coffee ingredients

There are over 1,000 active ingredients in coffee beans, not including the milk or sugar you might add to your finished cup. The coffee beans you buy from the store or your local coffee shop actually start as a fruit: coffee beans grow inside a coffee cherry before they are harvested, extracted, and roasted to make the beans we use for coffee.

Here are some of the main ingredients in coffee and a brief description of what they are and how they function in our bodies:


This is the big one: caffeine is an alkaloid plant toxin that is used to treat a number of ailments such as migraine headaches, gallbladder disease, asthma, and dermatitis. Caffeine is the drug of choice for the world, as the coffee industry produces more than 16 billion pounds of beans each year. Caffeine stimulates the central nervous system, makes us feel alert, and temporarily relieves drowsiness and fatigue (the “temporary” caveat is an important lesson further below).


Tannins are natural, organic compounds found in coffee, tea, wine, berries, legumes, and some herbs and spices. Tannins can adversely block the absorption of iron in your body.


This is a water-soluble B-vitamin that occurs naturally in some foods and helps with energy metabolism and growth.


These substances are produced by all human cells and show up in coffee, tea, and chocolate. Caffeine is a type of xanthine.


A substance naturally occurring in foods, spermidine may increase cardiovascular health and longevity, and prevent some forms of cancer.


This chemical is naturally-occurring in foods that have a natural, smoky flavor. It is partially responsible for coffee’s taste but also partially responsible for coffee’s occasional, unfortunate side effects on our guts.

Citric Acid

Citric acid makes up a significant portion of the acids present in coffee, ultimately giving it that well-known acidity.

Chlorogenic Acid

Another acid present in coffee is chlorogenic acid, but about 50% is destroyed during the roasting process.

The stimulating effects of coffee are usually attributed to xanthine derivatives like these:

  • Theobromine
  • Caffeine
  • Theophylline
  • Trigonelline
  • Hypoxanthine

The characteristic flavor and color of coffee are both due to the existence of phenolic compounds:

  • 4-Ethylphenol
  • 2,4-Methylenediphenyl
  • 2,3,5-Trimethylphenol
  • 4-Methoxy-4-Vinylphenol
  • 2-Ethylphenol

Some phenolic compounds contain antioxidant properties and are found in large quantities in a cup of coffee, like ferulic acid.

Caffeine’s Effects on your Body

caffeines effect

The chemical most likely to blame for feelings of drowsiness after coffee is, surprisingly, caffeine.

There are all kinds of studies from health organizations and professionals attempting to determine whether or not coffee is healthy for us. The general consensus seems to be that coffee can actually have beneficial side effects for our long-term health but only when consumed in moderate quantities. Fortunately, “moderate” still gives us room for about four cups of coffee a day.

One of the main sources of debate, of course, is the presence of high levels of caffeine in coffee. Caffeine stimulates your central nervous system to make you feel awake and alert. It most likely works by blocking adenosine receptors in your brain.

This is what happens: neurons fire off throughout the day as your body moves causing a release of a neurotransmitter called adenosine. This chemical builds up throughout the day making you feel tired or fatigued. That’s one of the reasons why most of us feel tired at night.

Coffee works by attaching to the adenosine receptor in your brain and blocking its uptake, meaning your brain doesn’t register that you’re getting sleepier. That gives dopamine—another neurotransmitter that makes you feel good—a chance to get a jump start, giving you a jolt of energy at the same time your brain is tricked into thinking you aren’t tired.

This process can all start kicking in anywhere between 45 and 60 minutes after your first cup of coffee and last for about 4 to 6 hours. When the effects finally do stop, your body’s built-up adenosine supply may hit your brain all at once, creating what we commonly call the caffeine crash.

After all, coffee is not actually fixing your fatigue but is merely masking it for a few hours so you can experience increased focus, productivity, or performance. At the same time that caffeine tricks you into thinking you aren’t tired, it also tricks your body into being more active. This is why some people like to have a cup of coffee before a run or even before their morning meditation routine.

Blocking adenosine from getting into the brain means that there is extra space for stimulating neurotransmitters to move around. That movement results in extra neurons firing, which your pituitary gland quickly notices and thinks that something important is going on. In response, your pituitary releases adrenaline (also called epinephrine) which causes a number of physiological responses in your body—such as opening your airways and elevating your heart rate—that make you feel more energetic.

Because of this, the European Food Safety Agency (EFSA) recognizes that caffeine may aid in sports endurance and performance, though the exact effects remain inconclusive. That is one of the reasons that caffeine is now commonly added to sports drinks and pre-workout formulas.

Genetic Caffeine Metabolization

However, caffeine functions differently in everyone and it is possible to form a mild tolerance. Each person’s body is unique in the sense that we may not all process things quite the same way.

Remember caffeine’s ability to block adenosine receptors in your brain? If your brain does not regularly get enough adenosine, it will create more receptors. More adenosine receptors in your brain means that you will need more coffee to get the same effects from the caffeine. If that happens, you have likely built up a tolerance.

Anecdotally, there seems to be a wide discrepancy in how coffee affects people. Some people say that coffee makes them immediately jittery or anxious; others say that they don’t feel the effects of coffee for hours. Still, others claim their body just doesn’t function during the day until they’ve had their morning cup.

The answer may lie in our genetics: about a decade ago, a team of researchers at the University of Toronto led by Dr. Ahmed El-Sohemy discovered a gene that determines how quickly our bodies break down caffeine.

Depending on quickly or slowly your body metabolizes caffeine, you may experience the effects of coffee more immediately and for shorter periods of time, or more gradually and for longer periods of time.

This genetic difference may account for how some people feel sleepy after a cup of coffee while others are alert and ecstatic. 

Coffee and Dehydration

Coffee is a diuretic, meaning it causes the urge to urinate. You can get trapped in a vicious cycle of dehydration when you drink coffee to stay awake without replenishing your body with water.

After drinking coffee, you’ll likely have to go to the bathroom, where your body loses water. That loss of water causes your blood to thicken, moving more slowly and delivering less oxygen to your body. With less oxygen, your body will start to feel sluggish and tired.

You may find yourself reaching for another cup of coffee, which will start the cycle all over again and certainly not help you stay awake.

However, recent research by a team of scientists at the University of Connecticut conducted a study in healthy adults that proved coffee is no more a diuretic than water is. The urban myth that coffee is dehydrating may not be true after all.


While coffee may not be dehydrating, it does act as a vasoconstrictor. In other words, the caffeine in coffee can actually shrink your blood vessels and reduce blood flow. This is one of the reasons that caffeine is a component of many medical drugs.

So while caffeine does increase your mental clarity, it can also reduce blood flow to your brain, which can make you feel foggy. Scientists noticed that a significant reduction in cognitive function after drinking coffee only appeared in people who drank large quantities of coffee.

If you’re feeling sleepy or sluggish and think the culprit may be coffee, it might be time to cut back on the amount of coffee you’re consuming. There is no need to cut out coffee entirely, but do enjoy in moderation.

Sugar and Sweet Coffees

sugar on coffee

If you add a lot of sugars or flavorings to your coffee, your drowsiness may be due to a sugar crash. Sugar is metabolized in the body much faster than caffeine, meaning its effects will wear off sooner and leave you feeling tired and sluggish.

Coffee, and more specifically the caffeine in coffee, may also cause hypoglycemia. Though the mechanisms for this are unclear, caffeine can disrupt glucose levels. If those levels dip too low, you can experience the symptoms of hypoglycemia, which include fatigue, headache, mood changes, and heart palpitations. In other words, it can make you feel tired.

The good news is that as long as you do not have existing medical conditions and are not currently diagnosed with hypoglycemia, moderating how much coffee you drink can prevent these side effects.

A Perfect Storm

It is likely that a mixture of all of the factors described above are at work making you feel tired after drinking coffee. Perhaps the most compelling factor is genetics.

If you are just recently getting into coffee and notice that it makes you feel tired, rather than alert and awake, it might be at least partially due to your genes. If you’ve been a fellow coffee lover for a while and just started noticing that you feel sleepy after your espresso, it may be that you have developed a caffeine immunity or that one or more of the factors above are at play. 

How to Drink Coffee Without the Side Effects

If either of those is you, then what next? We personally believe that everyone should be able to experience and love coffee the way we do, so try monitoring your coffee intake so you can enjoy it without experiencing some of those nasty side effects.

First, make sure you aren’t consistently over-doing it with coffee. We’ll admit, there are days that we go way past the recommended amount, but regularly consuming large quantities of coffee can have some of the effects above that make you sleepy.

The FDA recommends no more than 400 mg of caffeine per day. A regular 8 oz cup of coffee contains about 95 mg of caffeine so you can drink somewhere around 4 cups of coffee without experiencing adverse side effects.

To avoid the possibility of dehydration, make sure you drink enough water throughout the day. This is good health advice in any scenario: how much water you need per day depends on your age, sex, and level activity. However, it seems to be a good idea to get somewhere between 2.5 - 3.5 liters of water in your body per day.

Remember that coffee is not a replacement for sleep, no matter how much we might begin to rely on it as such. Because coffee’s effects can last up to 6 hours, it’s good to stop drinking coffee several hours before you want to wind down for the evening so you will be sure to get a good night’s rest. The more well-rested you are, the more you can enjoy coffee for its superb textures and flavors rather than thinking of it as your morning jolt of energy.

Finally, try weaning yourself off of sugary coffee drinks to prevent sugar crashes that may be leaving you drowsy by gradually reducing the amount of sugar you put in your coffee every day. Even better, follow the findings of a recent research study and cut yourself off cold turkey.

One of the more popular ways to curb the side effects of coffee and maximize the benefits is making your coffee into bulletproof coffee. There is some debate about how healthy this is for you, and we prefer our coffee straight, but the idea behind bulletproof coffee is to combine coffee with high amounts of healthy fats so that the caffeine is metabolized differently in your body and prevents afternoon caffeine crash. Check out this video if you are interested in learning more (see below).

About the Author Greg Haver

Hey there, my name is Greg and I'm the creator and editor of Coffee or Bust. I've been in the coffee business for over a decade, and my goal is to help you make the best cup of coffee with recommended tips, tools, and tricks!