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Caffeine Is No Substitute for Sleep

Stimulants Cannot Replace Lost Sleep


Updated February 13, 2013

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Caffeine Is No Substitute for Sleep
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There was simply too much to do yesterday, and you were late getting to bed. Again. The day started early, as it always does, and you simply did not get enough sleep. You drag yourself out of bed, wishing you had more time to get the sleep that you know you need. Wouldn’t it be nice to drink or eat something and make up for the sleep that you lost? Caffeine may be an easily accessible and attractive option. How does caffeine affect sleepiness? Can caffeine ultimately serve as a substitute for sleep? Consider how caffeine improves sleepiness and the limits of its effects.

What Is Caffeine?

Caffeine is a naturally occurring stimulant that is found in common drinks, foods, and medications. It is consumed throughout the world on a daily basis, often upon awakening. Caffeine is found in coffee beans, tea leaves, cocoa beans, and kola nuts. It is added to soft drinks (typically known as soda or pop). In more recent years, it has been increasingly consumed as part of energy drinks. Chocolate is another frequent source. There are also compounded caffeine pills available over the counter to aid alertness.

How Does Caffeine Affect Sleepiness?

Caffeine acts on the brain to increase alertness and vigilance, effectively extending wakefulness. How does caffeine work? In order to understand how caffeine works, it is necessary to consider another chemical within the brain called adenosine.

Adenosine is present throughout the body and is associated with our cells’ ability to use stored energy. It is also a chemical messenger, or neurotransmitter, that has a key role in the brain. Most importantly, it leads to the initiation of sleep. The longer a person stays awake, the more that adenosine accumulates in a region that promotes arousal or wakefulness. Imagine this chemical building up and clogging the machinery meant to keep us awake. When the interference is sufficient, we fall asleep. Caffeine works by blocking the cell receptors for adenosine. This means that more adenosine can build up before its effect of promoting sleepiness occurs.

Caffeine Is Not Sleep

Unfortunately, there are limits to the effects of caffeine in stimulating wakefulness. Though it is able to counteract some of the adenosine that builds up in the brain, eventually the levels overwhelm this blockade. To better understand this, it may be helpful to consider what contributes to the ability to sleep (or, conversely, to stay awake).

There are two processes that direct whether we are awake or asleep: homeostatic sleep drive and circadian rhythm. It is the gradual accumulation of adenosine within the brain that contributes to sleep drive. In simple terms, the longer a person stays awake the more likely they are to fall asleep. Insufficient sleep, such as occurs with sleep deprivation, will increase the natural drive, or desire, to sleep.

Sleep deprivation will occur anytime that an inadequate amount of sleep is obtained. This threshold will vary for each person. Even though the average amount of sleep needed may be 7 to 8 hours, some people need 9 or 10 hours. If you need 10 hours of sleep to wake feeling rested – and you only obtain 8 – you will be sleep deprived and suffer the ill effects. Caffeine may counteract some of this shortfall, but it cannot replace the sleep that did not occur.

Though we may not fully understand its role, sleep is a vital and important part of life. Circadian patterns linked to the patterns of day and night direct all that lives. From the simplest of creatures extending throughout the diversity of organisms, life is replenished and sustained by sleep. As William Shakespeare said in Macbeth, sleep is "Chief nourisher in life’s feast." Humans cannot survive without air, food, water – and, just the same, we must have sleep.

There is no substitute for a loss of sleep. Though a dose of caffeine may transiently improve concentration or attention, its effects are limited. It cannot take the place of a good night’s rest. Chronic sleep deprivation will not be alleviated by it. Caffeine can be an enjoyable complement to sufficient sleep, but it is not a replacement for it. In our hectic world we may try to supplant sleep with the use of products meant to take its place, but nature teaches us this is a futile endeavor.

If you find yourself relying on caffeine to get through your day, you may look to whether insufficient time spent sleeping may be the underlying culprit. For those with sleep disorders, poor quality sleep may also contribute to daytime difficulties. Start by giving yourself enough time to rest, and if this does not prove to be enough, speak with your doctor about your difficulties. For many, it may be time to put down the cup of coffee and get to sleep.


Kryger, MH et al. "Principles and Practice of Sleep Medicine." ExpertConsult, 5th edition, 2011.

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