According to the National Coffee Association and the Special Coffee Association of America, over 50% of Americans over 18 drink coffee every day. The sale of caffeine is so profitable that specialty coffee sales are increasing by 20% per year and account for more than $1.4 billion in the coffee market here in the United States. Clearly, many people like coffee (myself included). We primarily drink coffee because it helps us stay energized and alert, but how exactly does coffee work to help us do the things we need to do?

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The primary ingredient in coffee that contributes to the stimulation of the body's nervous system is caffeine. Caffeine is the world's most widely consumed psychoactive drug in the world and, unlike many other psychoactive drugs, caffeine is not illegal. Also, it's usually not regulated in most parts of the world. To understand how caffeine works, we will need to understand the function of another chemical compound, adenosine.

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Adenosine is a compound that helps the transfer of cellular energy in the body. If you've heard of the term "ATP" (adenosine triphosphate) before, it was likely in a high school biology class. ATP is one of the molecules that can be formed by adenosine in order to produce energy that is used by the entire body. In the brain, adenosine acts as an inhibitory neurotransmitter. That is, adenosine is a chemical that suppresses the activity of the central nervous system. This is why we feel drowsy near bedtime, adenosine is partly responsible for promoting sleep and suppressing the feeling of arousal.

This is where caffeine comes in to play, and this is how it works: caffeine blocks adenosine from entering nerve cells (neurons). To a nerve cell, the structure of caffeine looks very similar to adenosine. Because of this, caffeine binds to the receptors on the neurons that is mainly occupied by adenosine. As caffeine blocks these adenosine receptors, adenosine cannot get into these neurons, which means that these chemicals cannot work to depress the central nervous system. This is why you feel more alert when you drink caffeine. Caffeine also contributes to an increase in heart rate and blood pressure, as well as pupil dilation.

When the caffeine finally wears off, however, caffeine detaches from these adenosine receptors and adenosine can continue to reoccupy these receptors, making you crash and feel sleepy once again.

And there you have it! A brief intro into the fascinating science of caffeine–knowledge that you can share with your fellow coffee-holics over the breakfast table.