Something like 90%
of Americans consume caffeine in one form or another every
single day. More than half of all American adults consume more
than 300 milligrams (mg) of caffeine every day, making it
America's most popular drug by far. The caffeine comes in from
things like coffee,
tea, cola, chocolate,
Have you ever wondered what it is that makes caffeine so
popular? What does this drug do that causes its use to be so
widespread? In this edition of HowStuffWorks,
you will learn all about caffeine.
What is Caffeine?
Caffeine is known
medically as trimethylxanthine, and the chemical formula is
C8H10N4O2 (see this
page for an image of the molecular structure). When
isolated in pure form, caffeine is a white crystalline powder
that tastes very bitter. The chief source of pure caffeine is
the process of decaffeinating
coffee and tea.
Medically, caffeine is useful as a cardiac stimulant and
also as a mild diuretic (it increases urine production).
Recreationally, it is used to provide a "boost of energy" or a
feeling of heightened alertness. It's often used to stay awake
longer -- college students and drivers use it to stay awake
late into the night. Many people feel as though they "cannot
function" in the morning without a cup of coffee to provide
caffeine and the boost it gives them.
Caffeine is an addictive drug. Among its many
actions, it operates using the same mechanisms that
amphetamines, cocaine and heroin use to stimulate the brain. On a
spectrum, caffeine's effects are more mild than amphetamines,
cocaine and heroin, but it is manipulating the same channels,
and that is one of the things that gives caffeine its
addictive qualities. If you feel like you cannot function
without it and must consume it every day, then you are
addicted to caffeine.
Caffeine in the Diet
naturally in many plants, including coffee
beans, tea leaves and cocoa
nuts. It is therefore found in a wide range of food
products. Caffeine is added artificially to many others,
including a variety of beverages. Here are the most common
sources of caffeine for Americans:
By looking at these numbers and by knowing how
widespread coffee, tea and cola are in our society, you can
see why half of all American adults consume more than 300 mg
of caffeine per day. Two mugs of coffee or a mug of coffee and
a couple of Cokes during the day are all you need to get you
there. If you sit down and calculate your caffeine consumption
during a typical day, you may be surprised. Many people
consume a gram or more every single day and don't even realize
- Typical drip-brewed coffee contains 100 mg per 6-ounce
cup. If you are buying your coffee at Starbucks or a
convenience store or drinking it at home or the office out
of a mug or a commuter's cup, you are consuming it in 12-,
14- or 20-ounce containers. You can calculate the number of
milligrams based on your normal serving size.
- Typical brewed tea contains 70 mg per 6-ounce cup.
- Typical colas (Coke, Pepsi, Mountain Dew, etc.) contain
50 mg per 12-ounce can. Things like Jolt contain 70 mg per
- Typical milk chocolate contains 6 mg per ounce.
- Anacin contains 32 mg per tablet. No-doz contains 100 mg
per tablet. Vivarin and Dexatrim contain 200 mg per tablet.
Caffeine in the Body
Why do so many people
consume so much caffeine? Why does caffeine wake you up? By
understanding the drug's actions inside the body you can see
why people use it so much.
In the HowStuffWorks article How Sleep
Works, the action of adenosine is discussed. As
adenosine is created in the brain, it binds to adenosine
receptors. The binding of adenosine causes drowsiness by
slowing down nerve cell activity. In the brain, adenosine
binding also causes blood vessels to dilate (presumably to let
more oxygen in during sleep).
To a nerve cell, caffeine looks like adenosine. Caffeine
therefore binds to the adenosine receptor. However, it doesn't
slow down the cell's activity like adenosine would. So the
cell cannot "see" adenosine anymore because caffeine is taking
up all the receptors adenosine binds to. So instead of slowing
down because of the adenosine level, the cells speed up. You
can see that caffeine also causes the brain's blood vessels to
constrict, because it blocks adenosine's ability to open them
up. This effect is why some headache medicines like Anacin
contain caffeine -- if you have a vascular headache, the
caffeine will close down the blood vessels and relieve it.
So now you have increased neuron firing in the
brain. The pituitary gland sees all of the activity and thinks
some sort of emergency must be occurring, so it releases
hormones that tell the adrenal glands to produce adrenaline
(epinephrine). Adrenaline is the "fight or flight"
hormone, and it has a number of effects on your body:
explains why, after consuming a big cup of coffee, your hands
get cold, your muscles tense up, you feel excited and you can
feel your heart beat increasing.
- Your pupils dilate.
- Your breathing tubes open up (this is why people
suffering from severe asthma attacks are sometimes injected
- Your heart
vessels on the surface constrict to slow blood flow from
cuts and also to increase blood flow to muscles.
Blood pressure rises.
- Blood flow to the stomach slows.
- The liver releases sugar into the bloodstream for extra
- Muscles tighten up, ready for action.
Caffeine also increases dopamine levels in the same
way that amphetamines do (heroine and cocaine also manipulate
dopamine levels by slowing down the rate of dopamine
re-uptake). Dopamine is a neurotransmitter that, in certain
parts of the brain, activates the pleasure center. Obviously,
caffeine's effect is much lower than heroin's, but it is the
same mechanism. It is suspected that the dopamine connection
contributes to caffeine addiction.
So you can see why your body might like caffeine in the
short term, especially if you are low on sleep and need to
remain active. Caffeine blocks adenosine reception so you feel
alert. It injects adrenaline into the system to give you a
boost. And it manipulates dopamine production to make you feel
The problem with caffeine is the longer-term effects, which
tend to spiral. For example, once the adrenaline wears off,
you face fatigue and depression. So what are you going to do?
You take more caffeine to get the adrenaline going again. As
you might imagine, having your body in a state of emergency
all day long isn't very healthy, and it also makes you jumpy
The most important long-term problem is the effect that
caffeine has on sleep. Adenosine reception is important
to sleep, and especially to deep sleep. The half-life of
caffeine in your body is about 6 hours. That means that if you
consume a big cup of coffee with 200 mg of caffeine in it at
3:00 PM, by 9:00 PM about 100 mg of that caffeine is still in
your system. You may be able to fall asleep, but your body
probably will miss out on the benefits of deep sleep. That
deficit adds up fast. The next day you feel worse, so you need
caffeine as soon as you get out of bed. The cycle continues
day after day.
This is why 90% of Americans consume caffeine every day.
Once you get in the cycle, you have to keep taking the drug.
Even worse, if you try to stop taking caffeine, you get very
tired and depressed and you get a terrible, splitting headache
as blood vessels in the brain dilate. These negative effects
force you to run back to caffeine even if you want to stop.
If you are interested in breaking the caffeine cycle in
your own life, the book Caffeine
Blues (especially Chapter 10) can be very helpful.
For more information on caffeine and related topics, check
out the links on the next page.
Lots More Information!
More Great Links