How Exactly Does Caffeine Keep You Awake?

Whether you are a tea or a coffee person, caffeine is the ingredient that keeps you hooked. But how does it work?
Christopher McFadden

Whether you are a coffee connoisseur or a "tea-totaler" (we tried), your weapon of choice for a pick-me-up in the morning is caffeine. But have you ever wondered how this wonder-drug actually works?

Here we explore, briefly, what exactly caffeine is, and how it affects your body. 


What is caffeine and how does it work?

Caffeine is classified as a central nervous system stimulant of the methylxanthine class. It is also the world's most widely consumed psychoactive drug. 

Unlike many other psychoactive drugs (affects the central nervous system), caffeine is widely legalized and tends to be unregulated. In its pure form, caffeine is a bitter, white crystalline purine that is chemically related to the adenine and guanine bases found in RNA and DNA. 

It is a component of many natural products in the world but is most commonly found in the seeds, nuts, and leaves of a number of plants (tea and coffea being most common) native to Africa, East Asia, and South America. In nature, caffeine acts as a means of protection against predation and suppresses nearby seed germination. 

Caffeine is famed for its "pick me up" qualities, but how exactly does it work? In order to answer this, we'll need to understand a little bit about the impacted functions of our brains' work.

While you are awake, the neurons of your brain fire away and produce a neurochemical called adenosine as a byproduct. Adenosine is also a purine and is a base nucleoside.

But apart from that, adenosine is also used in many processes in your body. Adenosine plays an important role in your immune, nervous, circulatory, respiratory and urinary systems. 

Given that its biologically important, the levels of this waste product are constantly monitored by your central nervous system through a vast network of receptors. When adenosine hits a certain threshold in your spinal cord and brain, your body reacts to start the process of making you go to sleep.

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"As adenosine is created in the brain, it binds to adenosine receptors. This binding causes drowsiness by slowing down nerve cell activity. In the brain, this also causes blood vessels to dilate, most likely to let more oxygen into that organ during sleep." -

There are several types of adenosine receptors throughout your body, one of which, A1 receptors, just happens to be affected by caffeine. 

how caffeine works coffee beans
Sourceolle svensson/Flickr

Caffeine, when ingested in sufficient quantities (usually about 100 to 200 mg) works its way towards these receptors and mimics the effects of natural adenosine by binding to it. But, unlike adenosine, caffeine does not slow down the workings of the receptor's cell; quite the opposite. 

By doing this, you body is tricked into thinking that it is not yet time to sleep thus making you "feel" more awake. Caffeine also causes the blood vessels in the brain to constrict, blocking the natural tendency of adenosine to dilate them. 

It is, for this reason, some medications like Anacin (taken for headaches) tend to be less effective if you ingest caffeine. But that is only half the story.

How does caffeine work to keep you awake?

As adenosine is blocking from binding to receptors, other neurotransmitters like dopamine and glutamate are able to build up in your system.

Dopamine swells giving you that "hit" effect when you drink a strong coffee. 

But caffeine is something of a double-edged sword. While it can give you a boost from time to time, the effect is only shortlived. It is estimated that it takes around four cups of coffee to block half the A1 receptors in your body.

With that many receptors blocked, adenosine soon builds up in the body with nowhere to go. When your body does finally metabolized the caffeine in its system, the built-up adenosine floods the A1 receptors. 

It takes some time for your body to deal with the extra workload of natural adenosine which makes you feel very groggy, often more so than before you binged on coffee. But, the efficacy of this process completely depends on the individual; specifically their tolerance, genetics, and other physiological characteristics. 

"But generally, caffeine lasts about five to six hours in the body before wearing off. For women taking birth control pills and for women between ovulation and the beginning of menstruation, it takes about twice as long to process the caffeine. For regular smokers, their bodies take half as long to process caffeine." - 

While drinking coffee may appear to give you a boost in energy, it is no way a substitute for any lost sleep.

What are the effects of caffeine withdrawal on a person?

You may, or may not be a caffeine addict, but continual consumption of caffeine products will eventually enable you to build up a tolerance to it. Typically it takes between a week and 12 days for somebody to develop a decent tolerance to caffeine drinking just one daily dose.

But for those who consume significant amounts of caffeine a day, caffeine addiction can have some serious implications for your health. 

Addiction to and dependence on caffeine, like any other drug, can negatively impact your health and social interactions, as well as other parts of your life. 

"While most caffeine users feel they enjoy many of the effects of caffeine, like a good "morning boost," they may not be aware of some of the negative effects the drug is having, such as disrupted sleep, irritability, and anxiety. Many people, for example, get into a vicious cycle of drinking coffee to increase energy, only to find themselves both fatigued and unable to relax at bedtime." -

Like many other drugs, like nicotine for example, when you stop your daily intake, your tolerance begins to drop and withdrawal symptoms begin to appear.

These symptoms can develop quite quickly with between 12 and 24 hours being the norm. This is usually the main reason for your morning craving for some coffee; to ward off the withdrawal.

One of the most common symptoms is a mild headache, but more serious ones can include depression, fatigue, lethargy, irritability, nausea, and even vomiting. Withdrawal symptoms typically last for about 10 days until the withdrawal process is complete. 

For those who want to kick their dependence on caffeine, it is recommended that you reduce your daily intake gradually over time. The easiest way is to increasingly substitute a caffeine drink with a decaffeinated or non-caffeinated alternative overtime to avoid stave off their worst withdrawal symptoms. 

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