How Caffeine works...

Or: Why you can't wake up without it...

Ever wonder why you enjoy your morning cup of brown-black coffee so much that you keep coming back for more? I mean, let's face it, coffee is an acquired taste, and it doesn't taste all that good. But oh, that rich nutty smell can make you turn right around and run for the percolator. You imbibe your daily quota and it makes cubicle existence bearable; the joys of java. If you're like me, and you drink coffee as a hobby, you may find this mildly interesting, or if you like it for it's hyperactive properties instead, you might want to read further and find out how caffeine works it's late-night magic.

The Caffeination of Society

It is widely estimated that somewhere between 80%-90% of American's consume caffeine in some form every day. If you find yourself included in that 90%, you most likely consume over 300 milligrams (mg.) of caffeine per day. I won't get into where you obtain said caffeine or how much is in various products, as those sources have been adequately treated in previous nodes:

I'm sure you can find more as well.

Caffeine is by far America's favorite drug, but I am a little curious as to how much caffeine our counterparts in England consume. Do you drink decaffeinated tea?


  • ascorbic says re caffeine: We brits drink plenty of caffeine. Lots of coffee as well as good strong high-caffeine-but-not-as-high-as-coffee tea.
  • evilrooster says re caffeine: The British do not drink decaffeinated tea as a rule. It is held to be vile, and is not readily available (unlike decaf coffee). They do drink much, much more instant coffee than Americans.

Medically, Caffeine is known as trimethylxanthine. The chemical formula is C8H10N4O2. When isolated, primarily sourced in the decaffeination process for coffee and tea, pure caffeine is found as a white powder. This powder can be extremely potent, and estimates for LD-50, or the average intake amount for overdose, is somewhere close to 10 grams.

Caffeine has a number of medical uses. Most often it is used as a cardiac stimulant or mild diuretic. Caffeine is most often used recreationally, not medically, to stay awake and/or boost energy. It is enjoyed in many forms and variations including the typical coffee, tea, soda, and chocolate.

The average cup of coffee (6 ounces) has about 100 mg of caffeine in it. If you drink coffee from Starbucks, or pretty much any other coffee store, shop, or house, you drink 12, 16, or 20-ounce servings. As you can see, it adds up fast. Think "commuter-mug" and you're looking at just one of the servings many people throw back to start their day. If you drink one 20-ounce Starbucks coffee, you have already hit the average of 300 mg. A can of Coke has roughly 50 mg per 12 ounces. Two Cokes, and one "small" (or whatever they call it) Starbucks coffee, and you've hit the average. How far over the average are you?

Caffeine is an extremely addictive drug, both physically and mentally. The physical addiction of coffee is similar, though less potent, to amphetamines, heroin, and cocaine. These narcotics have similar mechanics, when introduced to the body, as caffeine does. Generally, caffeine is a milder stimulant than amphetamines, heroin, or cocaine, but employs similar methods of stimulus.

But you already knew all of this....

Why Caffeine Makes You Happy

Caffeine is absorbed readily through the stomach and small intestine into the bloodstream. Not quite mainlining, but it passes with relative ease. The severity of the result depends on exactly how much caffeine hits your unsuspecting cranium. Your brain is the epicenter for your caffeine-induced buzz.

While you are awake, cells in your brain produce a substance called adenosine. This substance is the byproduct of cell activity in the brain, and is picked up by adenosine receptors. Adenosine bonds to these receptors in the brain and, as levels of adenosine increase, eventually causes nerve cell activity to slow down considerably. The result is drowsiness, and ultimately, sleep.

Caffeine interferes with this process. It binds to the adenosine receptors and blocks adenosine created in the brain from finding the receptors. Now your brain becomes unable to see any further adenosine produced in the brain, and your nervous system begins to speed up.

The direct results of your nervous system speeding up are usually very apparent:

  • heart beats faster
  • pupils dilate
  • increased blood flow to muscles
  • increased blood sugar
  • blood vessels in the brain constrict
  • blood vessels at the surface of the skin contract (this is why you get cold hands after drinking a lot of coffee)
  • tremors, irritability, and nervousness
  • increased respiration

Caffeine also affects headaches: Medical effects of caffeine on headaches.

Your pituitary gland sees all this increased nerve activity and wants to get a piece of the action. It starts to pump out hormones that tell the adrenal glands to start manufacturing adrenaline (epinephrine), and this causes your body to kick into a higher gear. Your body, and your brain, is now prepared to take on the world. This simulates, to a lesser extent, the "fight or flight" effect of a large adrenaline rush in response to a dangerous situation.

The last, and probably the most important effect of caffeine, is increased dopamine levels in your brain. Similar to drugs like heroin and cocaine but in smaller amounts, caffeine prevents the recycling of dopamine in the brain. This increases dopamine levels over the length of time caffeine resides in your system. Dopamine is a neurotransmitter and it causes pleasurable sensations in your brain. It is speculated that this may lead to some of the addictive properties of caffeine.

Caffeine does have some negative effects on your body. The cycle that develops with caffeine causes people to drink more as they "come down" off of their caffeine buzz. You drink more, you get more adrenaline, and you're back on top. Your body sees this as a heightened state of alert all day long. Not good over a long period of time.

Caffeine resides in the body for a half-life of 5-7 hours on average, but depends on metabolism, blood-flow, and a variety of other factors. Smokers and young children typically have a shorter caffeine half-life, while pregnant women, women taking oral contraceptives, and people with liver disease can have much longer half-lives. A pregnant woman may have a half-life for caffeine in the body between 18 and 20 hours.

It stands to reason that drinking coffee late in the day will have residual effects well into the evening. Caffeine prevents the body from entering the deepest part of sleep, and the result is sleep that is less rejuvenating than the norm. After a night of less restful snoozing, you'll go right to the coffee pot in the morning to help you cope with the foggy-head you wake with. This perpetuates the cycle, injecting your body with fun stuff like adrenaline, dopamine, and adenosine blocking goodness. Then, you crash. Somewhere around noon you get tired. You eat some food, get sleepy, and then you drink more coffee. The cycle continues, and your sleep the next night is less than beautiful. Ultimately, caffeine can prevent deep, restful, or prolonged sleep, which can lead to a cycle of increased caffeine intake.

So you see, caffeine does have some side-affects. This write-up attempts to explain the basics of why you like caffeine, and how it works it's magic. There are some health concerns that can be increased, or created with excessive caffeine intake, but that's a story for another node...



Caffeine, aka:


It has a boiling point of 352 F (178 C) (sublimes), a melting point of 460 F (238 C), and a specific gravity of 1.2. Slight fire hazard when exposed to heat or flame.

<cough> I'm ok. really. I promise. what??? I only had one cup. promise. really. stop looking at me like that... that is not my mug! where? I don't see any! quick, KILLIT!!HITIT!!HIT!!DIE!!!!

Here's some interesting trivia from the caffeine FAQ:
  • The lethal dose of caffeine for the average adult is somewhere around 10 grams (between 50 and 200 cups of coffee). This also has a lot to do with tolerance levels.
  • Caffeine has a bitter flavor. Barq's Root Beer adds caffiene as a flavouring agent for it's "bite".
  • A UPI article states "A major study has found fewer suicides among coffee drinkers ..."
This FAQ available at

structural formula for caffeine:

     H   H
      \ /
  H -- C        O     H   H
        \      //      \ /
         N -- C         C -- H
        /      \       /
  O == C        C --- N
        \      //      \
         N -- C -- N == C -- H
  H -- C       caffeine     
      / \      (C8H10N4O2)
     H   H                    

I've found that caffeine actually puts me to sleep. Initially, it is a stimulant; but if I get too much, about an hour later (much less than the half life mentioned above), I'll be unable to keep awake. About a year after I discovered why I couldn't keep awake after lunch, I actually read a study that said that caffeine has some other side effects, such as reducing the brain's ability to use sugar. I don't know if this is relevant to me or not, but I suppose being hypoglycemic doesn't help here.

Also, some stimulants are known to act as calmatives to people with ADD.

Interestingly, pure caffeine is extremely toxic and must be handled with extreme safety. If this isn't enough to convince you, this is the warning label for pure caffeine:


Scary, eh?

Caffeine Content of Foods and Drugs

Product: Serving Size, Caffeine (mg)

OTC Drugs

NoDoz, maximum strength; Vivarin: 1 tablet 200

Excedrin: 2 tablets 130

NoDoz, regular strength: 1 tablet 100

Anacin: 2 tablets 64


Coffee, brewed: 8 ounces 135

General Foods International Coffee, Orange Cappuccino: 8 ounces 102

Coffee, instant: 8 ounces 95

General Foods International Coffee, Cafe Vienna: 8 ounces 90

Maxwell House Cappuccino, Mocha: 8 ounces 60-65

General Foods International Coffee, Swiss Mocha: 8 ounces 55

Maxwell House Cappuccino, French Vanilla or Irish Cream: 8 ounces 45-50

Maxwell House Cappuccino, Amaretto: 8 ounces 25-30

General Foods International Coffee, Viennese Chocolate Cafe: 8 ounces 26

Maxwell House Cappuccino, decaffeinated: 8 ounces 3-6

Coffee, decaffeinated: 8 ounces 5


Celestial Seasonings Iced Lemon Ginseng Tea: 16-ounce bottle 100

Bigelow Raspberry Royale Tea: 8 ounces 83

Tea, leaf or bag: 8 ounces 50

Snapple Iced Tea, all varieties: 16-ounce bottle 42

Lipton Natural Brew Iced Tea Mix, unsweetened: 8 ounces 25-45

Lipton Tea: 8 ounces 35-40

Lipton Iced Tea, assorted varieties: 16-ounce bottle 18-40

Lipton Natural Brew Iced Tea Mix, sweetened: 8 ounces 15-35

Nestea Pure Sweetened Iced Tea: 16-ounce bottle 34

Tea, green: 8 ounces 30

Arizona Iced Tea, assorted varieties: 16-ounce bottle 15-30

Lipton Soothing Moments Blackberry Tea: 8 ounces 25

Nestea Pure Lemon Sweetened Iced Tea: 16-ounce bottle 22

Tea, instant: 8 ounces 15

Lipton Natural Brew Iced Tea Mix:, diet 8 ounces 10-15

Lipton Natural Brew Iced Tea Mix, decaffeinated: 8 ounces 5

Celestial Seasonings Herbal Tea, all varieties: 8 ounces 0

Celestial Seasonings Herbal Iced Tea, bottled: 16-ounce bottle 0

Lipton Soothing Moments Peppermint Tea: 8 ounces 0

Soft Drinks

Josta: 12 ounces 58

Mountain Dew: 12 ounces 55.5

Surge: 12 ounces 52.5

Diet Coke: 12 ounces 46.5

Coca-Cola classic: 12 ounces 34.5

Dr. Pepper, regular or diet: 12 ounces 42

Sunkist Orange Soda: 12 ounces 42

Sky Rocket caffeinated syrup: 1200.0

Afri-Cola: 250 Pepsi-Cola: 12 ounces 37.5

Barqs Root Beer: 12 ounces 22.5

7-UP or Diet 7-UP: 12 ounces 0

Barqs Diet Root Beer: 12 ounces 0

Caffeine-free Coca-Cola or Diet Coke: 12 ounces 0

Shasta Cola: 44.4

Caffeine-free Pepsi or Diet Pepsi: 12 ounces 0

Minute Maid Orange Soda: 12 ounces 0

Mug Root Beer: 12 ounces 0

Sprite or Diet Sprite: 12 ounces 0

Caffeinated Water

Java Water: 1/2 liter (16.9 ounces) 125

Krank 20: 1/2 liter (16.9 ounces) 100

Aqua Blast: 1/2 liter (16.9 ounces) 90

Water Joe: 1/2 liter (16.9 ounces) 60-70

Aqua Java: 1/2 liter (16.9 ounces) 50-60


Juiced: 10 ounces 60

Frozen Desserts

Ben & Jerry's No Fat Coffee Fudge Frozen Yogurt: 1 cup 85

Starbucks Coffee Ice Cream, assorted flavors: 1 cup 40-60

Häagen-Dazs Coffee Ice Cream: 1 cup 58

Häagen-Dazs Coffee Frozen Yogurt, fat-free: 1 cup 40

Häagen-Dazs Coffee Fudge Ice Cream, low-fat: 1 cup 30

Starbucks Frappuccino Bar: 1 bar (2.5 ounces) 15

Healthy Choice Cappuccino Chocolate Chunk or Cappuccino Mocha Fudge Ice Cream: 1 cup 8

Yogurts, one container

Dannon Coffee Yogurt: 8 ounces 45

Yoplait Cafe Au Lait Yogurt: 6 ounces 5

Dannon Light Cappuccino Yogurt: 8 ounces 1

Stonyfield Farm Cappuccino Yogurt: 8 ounces 0

Chocolates or Candies

Hershey's Special Dark Chocolate Bar: 1 bar (1.5 ounces) 31

Perugina Milk Chocolate Bar with Cappuccino Filling 1/3 bar: (1.2 ounces) 24

Hershey Bar: (milk chocolate) 1 bar (1.5 ounces) 10

Coffee Nips: (hard candy) 2 pieces 6

Cocoa or Hot Chocolate: 8 ounces 5

1 -- Serving sizes are based on commonly eaten portions, pharmaceutical instructions, or the amount of the leading-selling container size. For example, beverages sold in 16-ounce or half-liter bottles were counted as one serving.

2 -- Sources: National Coffee Association, National Soft Drink Association, Tea Council of the USA, and information provided by food, beverage, and pharmaceutical companies and J.J. Barone, H.R. Roberts (1996) "Caffeine Consumption." Food Chemistry and Toxicology, vol. 34, pp. 119-129.

from a CSPI press release

The LD-50 of caffeine (that is the lethal dosage reported to kill 50% of the population) is estimated at 10 grams for oral intake.

As it is usually the case, lethal dosage varies from individual to individual according to weight.
Ingestion of 150mg/kg of caffeine seems to be the average LD-50 for people. That is, people weighting 50 kilos have an LD-50 of about 7.5 grams, people weighing 80 kilos have an LD-50 of about 12 grams.

On one occasion it was reported that a man survived after ingesting 24 grams.
The minimum lethal dose ever reported was 3.2 grams taken intravenously (injected).

Acute caffeine poisoning gives early symptoms of anorexia, tremor, and restlessness. Followed by nausea, vomiting, and confusion. Serious intoxication may cause delirium, seizures, and hyperglycemia. Super high dose caffeine intake can lead to nervousness, irritability, anxiety, muscle twitching, insomnia, palpitations and hyperreflexia.

-Information from Desk Reference to the Diagnostic Criteria from DSM-3-R (American Psychiatric Association, 1987)

Caffeine has also been proven to slow and even stop the replication of DNA, which leads to lower sperm counts.

A Caffeine Overdose is classified as taking more than 250 mg in a 10-30 minute period, though this can change depending on body mass. An overdose of caffeine can result in nausea, vomiting, numbness in the fingers or toes, confusion, drowsiness, convulsions, and possibly death. -Information from WebMD, and Caffeine FAQ

More interesting facts about the effects of caffeine:

It has been documented that caffeine is a rather effective inhibitor of the DNA damage repair pathway in cells. Studies showed that caffeine inhibits the protein kinases ATM (Ataxia Telangiectasia Mutated) and ATR (ATM and Rad3-Related) 1. These kinases are activated by DNA damage and one of their functions is to stop the cell cycle. This gives the cell time to repair the DNA damage before continuing along the cycle. Inhibiting ATM and ATR therefore forces the cell to continue through the cycle with damaged DNA, potentially leading to permanent DNA mutations which could lead to cancer. Therefore caffeine is indeed a carcinogen, one of the warnings on a bottle of pure caffeine which can be seen in Jizz's writeup above.


Research also indicates that caffeine has anticancer properties as well. In one example, scientists have shown that treating mice with caffeine reduces the formation of skin tumors after exposure to UV rays2. This may not be due to caffeine's ability to inhibit ATM and ATR, but because it is also known to be an antioxidant. Obviously, many more tests need to be done to determine if caffeine has a therapeutic use in humans.

Therefore, it appears that caffeine is both a carcinogen and an anticancer agent. While this may seem odd, keep in mind that many, if not most, of the chemotherapy drugs that are currently used to treat cancer patients are potential carcinogens as well.

Don't start thinking that your cup of coffee will turn you into a mutant or be the miracle cancer cure, since the concentrations used in the above experiments are impossible to achieve with normal or even high consumption of caffeinated beverages.


1) Sarkaria J.N. et al., Cancer Research, 1999

2)Lu Y.P. et al., Proceedings of the National Academy of Sciences, 2002

Caf*fe"ine (?), n. [Cf. F. caf'eine. See Coffee.] Chem.

A white, bitter, crystallizable substance, obtained from coffee. It is identical with the alkaloid theine from tea leaves, and with guaranine from guarana.


© Webster 1913.

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