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Caffeine is a stimulant that promotes alertness.

Caffeine can have a disruptive effect on your sleep.

Caffeine should be used in moderation.

It is best if you avoid caffeine in the late afternoon and in the evening.

Sleep and Caffeine

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  • caffeine

Thomas M. Heffron  |  Aug 01, 2013
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Caffeine is a natural substance that can be extracted from plants. Natural sources of caffeine include coffee beans, tea leaves and cocoa beans. It also can be produced synthetically.  

Caffeine is a type of drug that promotes alertness. These drugs are called “stimulants.” Caffeine acts as an “adenosine receptor antagonist.” Adenosine is a substance in your body that promotes sleepiness. Caffeine blocks the adenosine receptor to keep you from feeling sleepy.

Caffeine begins to affect your body very quickly. It reaches a peak level in your blood within 30 to 60 minutes. It has a half-life of 3 to 5 hours. The half-life is the time it takes for your body to eliminate half of the drug. The remaining caffeine can stay in your body for a long time.

Coffee accounts for 54% of the caffeine consumption in the world. Tea accounts for another 43%. On any given day, about 85% of Americans use caffeine products. The average daily consumption of caffeine by adults in the U.S. is about 300 mg per person. This is about three times higher than the world average. But it is still only half of the caffeine consumption in heavy tea-drinking countries such as England and Sweden.

Caffeine is a product that has both positive and negative effects. These effects depend on the amount of caffeine you consume and when you consume it:

Positive Effects

Caffeine is considered a moderately effective alerting agent. It can have a positive effect on your reaction times, mood and mental performance. A normal dose of caffeine is about 50 mg to 200 mg.

Caffeine works best when you take it on an intermittent, off-and-on basis. Higher doses can have much more potent effects. A dose of 500 mg or 600 mg of caffeine can affect you much like a low dose of an amphetamine. The effects of caffeine wear off quickly when you use it regularly. Your body builds up a tolerance to it.

Negative Effects

Caffeine can have a disruptive effect on your sleep. The most obvious effect of the stimulant is that it can make it hard for you to fall asleep. One study also found that caffeine can delay the timing of your body clock. These effects will reduce your total sleep time. Caffeine also can reduce the amount of deep sleep that you enjoy. 

The effects of caffeine can occur even when you consume it earlier in the afternoon or evening. One study found that consuming caffeine 6 hours before bedtime reduced total sleep time by 1 hour. These effects also can be stronger in older adults. It takes their bodies a longer time to process caffeine. Regularly consuming high doses of caffeine may cause complications during pregnancy.

At high doses, caffeine can produce these common side effects:

  • Diarrhea
  • Sweating
  • Nausea
  • Increased heart rate
  • Increased breathing rate
  • Muscle tremors

Withdrawal symptoms can occur when you stop taking caffeine after using it regularly for a long time. These symptoms include:

  • Headaches
  • Sleepiness
  • Low energy levels
  • Bad moods

The FDA is investigating reports of illness, injury or death of people who took products marketed as “energy drinks” or “energy shots.” The FDA cautions consumers that products marketed as “energy shots” or “energy drinks” are not alternatives to sleep.

Some retailers sell pure caffeine powder in bulk. It is marketed as a dietary supplement. Parents need to be aware that many teens and young adults take it for an energy boost. Others consume caffeine powder in an attempt to enhance performance or lose weight.

Caffeine powder is highly potent, and a safe serving size is extremely small. It is nearly impossible to measure caffeine powder accurately in the home. As a result the risk of an accidental, lethal overdose is high.


Caffeine has both positive and negative attributes. It can be very effective for improving your concentration, alertness and energy. But these effects can be brief if you consume high doses of caffeine on a daily basis. Caffeine also can have a negative effect on your sleep. It can reduce the quantity and quality of your sleep. These effects can occur even when you are unaware of them.


Like most substances, you should use caffeine in moderation. These are some general guidelines for you to follow:

  • You should limit your caffeine consumption to no more than about 300 mg to 400 mg per day. This equals about three to four cups (8-oz) of coffee.
  • Women who are pregnant or nursing should consume even less caffeine or avoid it altogether.
  • Parents should limit the amount of caffeine that their children consume.
  • People with high blood pressure or other heart problems should avoid high levels of caffeine.
  • It is best if you avoid caffeine in the late afternoon and in the evening.
  • The FDA and the American Academy of Sleep Medicine advise consumers to avoid powdered pure caffeine.

Caffeine Levels

Caffeine levels vary widely from one product to another. In particular, the caffeine content of coffee can be very unpredictable. 

Scientists at the University of Florida bought a 16-oz cup of the same type of coffee from one coffee shop for six straight days. They analyzed each cup of coffee to determine how much caffeine it contained. They found a wide range of caffeine levels in the six cups of coffee. The lowest level was 259 mg of caffeine and the highest was 564 mg.

Coffee’s caffeine content depends on many factors. These include the type of bean that is used and how the coffee is prepared. In the same way, the size of a tea bag, number of tea leaves and brewing time can affect the caffeine level of a cup of tea.

Caffeine is added to many soft drinks. The U.S. Food and Drug Administration classifies caffeine as a substance that is “generally recognized as safe,” or GRAS. This means that caffeine is not regulated by the FDA as a food additive. It must appear as an added ingredient on a drink’s label. But the label does not need to show the amount of caffeine in the drink. 

The following table will help you compare the caffeine levels found in a number of common products:


Serving Size

Caffeine (mg)




Coffee, brewed

1 cup (8 oz)



1 oz


Coffee, instant

8 oz


Coffee, brewed, decaf

1 cup (8 oz)





Lipton Black Tea

1 cup


Lipton Original Iced Tea

16 oz


Tea, brewed

1 cup (8 oz)


Lipton 100% Green Tea

1 cup


Tea, instant, unsweetened

1 cup (8 oz)


Lipton Brisk Tea

12 oz


Tea, herbal

1 cup (8 oz)


Energy Drinks




16 oz



16 oz



16 oz


Full Throttle

16 oz



16 oz


Red Bull

12 oz
(16 oz equivalence)


Red Bull

8.4 oz
(2 can equivalence)





Pepsi One

12 oz


Mountain Dew

12 oz


Mello Yellow

12 oz


Diet Coke

12 oz



12 oz


Diet Pepsi

12 oz


Coca Cola Classic

12 oz


Caffeine free Coke, Pepsi

12 oz


Sprite, 7-Up

12 oz






1 tablet



1 tablet


Extra Strength Excedrin

2 tablets



2 tablets





Chocolate chips, semi-sweet

1 cup (6 oz bag)


Chocolate chips, milk chocolate

1 cup


Baking chocolate, unsweetened

1 square


Milk chocolate bar

1 bar (1.55 oz)


Chocolate pudding, ready-to-eat

Snack size (4 oz)


Frozen yogurt, chocolate

1 cup


Chocolate ice cream

1 cup


Hot cocoa

1 packet, 6 oz water


Chocolate syrup, fudge-type

2 tbsp


Chocolate-chip cookie, packaged

1 cookie


Note: Caffeine levels are estimates based on both the USDA National Nutrient Database for Standard Reference and information provided by manufacturers.

Updated March 25, 2017


  1. 1 Big nick 17 Apr
    ive been struggling to sleep for more than 4 hours and always wake to relieve my bladder at about 4 o'clock which is putting a massive strain on my life , the info I've got from this page has made me realise that I'm consuming around 600 mg per day which is very high so I'm going to try all decaf and decaf coke too
      great info  thanks
  2. 2 Anime is awesome 01 Apr
    I have a question, i am 12 years old and i was having an anime marathon and to ensure that i stayed awake i drank 2 cups of the via instant dark roast coffee from starbucks and the only symptoms that i am currently having are the urge to frequently pee, diarrhea, and like slight increase in heart rate but not by much but as i was curious about is how long does a slight caffeine overdose last in a 12 year old?
  3. 3 George 26 Nov
    To Pat who was annoyed that manufacturers don't inform us of caffeine content. So easy to google the name of the item plug "caffeine content". That would have beenquicker than typing your posting! As the poet said, "It's better to light a candle than to curse the darkness."
  4. 4 Saratop 12 Sep
    So I was consuming a pretty small amount of caffeine. At the very most 2 cups of tea and some chocolate (a small amount) Is it possible that that  could  give me sleep problems In the long term?
  5. 5 Marky 25 Jul
    Informative article. Just wondering what the cumulative effects of caffeine AND sugar are? Even more wakefulness, I'm guessing. I had a big Coke soda yesterday at 3 pm (thirsty) and found myself still awake after 2 am. I think the combination of caffeine and sugar in soda is a really troublesome combo.
  6. 6 Pat 02 May
    Seems highly unethical that companies are allowed to sell their drinks to us without telling us the caffeine content. I want to know what I'm drinking
  7. 7 Hazel 17 Apr
    GREAT information. Clear and comprehensive! Thank you.
  8. 8 Margaret Encinas 08 Apr
     Thank You for all this great information!  I think I'm doing pretty good.
  9. 9 Coffee drinker 26 Mar
    it is wonderful to have clear information like this readily available to the public.  Thank you
  10. 10 SirJean 01 Mar
    so, I've been laying in bed for hours, I've had a couple monsters today, this would explain my inability to sleep. I would like to say that if you drink energy drinks, don't take them after like 1pm as anytime after will affect your sleep badly. 
  11. 11 Gabriele 25 Feb
    Great piece, very informative, however I don't like it when it says that parents should "limit" the use of caffeine for children. Parents should just forbid caffeine to children. And I mean pepsi/coke in particular, the most common source of caffeine that kids have. Parents should limit instead the intake of sugar. 
  12. 12 Godo 02 Feb
    So the FDA recognizes it as GRAS... we can't have people thinking/knowing about how much caffeine they are consuming, can we?
  13. 13 Mike 28 Jan
    So in conclusion, some energy drinks contain more caffeine than prescribed pills. Nice.
  14. 14 Mike 24 Jan
    Im surprised there's not more comments after 2 1/2 yrs.  
    Great information.
    Thank you so very much!
  15. 15 Starbucks Addict 17 Jan
    I should lay off the Starbucks then. 
  16. 16 dragonslayer 112 05 Jan
    Really helpful for my OO speech.Thank you.
  17. 17 jelly belly 27 Dec
    This was very informative.