Chapter 7 - Caffeine

Learning Outcomes

After reading through this chapter, you should be able to:

  • Explain the effect of caffeine on bodily functions.
  • Understand the effect of caffeine on alertness.
  • Discuss the effect of caffeine on sleep.
  • Name symptoms of caffeine withdrawal. 

What is caffeine?

Caffeine is an addictive drug. You may be addicted to caffeine if you feel you cannot function without it and need to consume it every day. Caffeine occurs naturally in many plants including coffee beans, tea leaves, and cocoa nuts. It is also found in an array of food products and beverages such as chocolate and cola drinks.

If you drink caffeinated beverages, you are probably aware that caffeine perks you up. If you are low on sleep and need to remain active, caffeine can make you feel alert by blocking adenosine reception. Adenosine causes blood vessels to dilate and nerve cell activity to slow down, causing drowsiness. After drinking coffee, you may notice that your hands get cold, your muscles tense up, you feel excited, and your heart beats faster.

It takes caffeine approximately 20 minutes to enter your system, and the effects can last up to six hours. You should avoid having your last caffeinated drink too close to bedtime. The stimulant effect may reduce your chance of falling asleep.

Strategic use of caffeine

Most people don’t use caffeine as effectively as they could. They tend to drink it when they are not really tired, which means the stimulating effect doesn’t have much impact. Regular caffeine consumption leads to increased tolerance, which means that over time we get less effect from the same quantity. When you have a high tolerance to caffeine, drinking one or two cups when you are really tired may make little difference to your alertness.

People who are addicted to caffeine often experience withdrawal effects when they stop drinking it. These include a dull headache that lasts from one to five days, irritability, nervousness, restlessness, and sleepiness. In extreme cases, nausea and vomiting have been reported.

To use caffeine more effectively, start by being more strategic about when you drink it. Here are a number of tips on how to use caffeine to its best advantage:

  • Avoid drinking caffeinated drinks when you are not tired. The caffeine will have little effect and will contribute to increasing your caffeine tolerance. Your body will get used to having it and, over time, you will need to drink more to get the same effect.
  • Avoid drinking caffeinated drinks in the morning. The early part of the day is a time when your body is waking up naturally and, generally speaking, you will feel more awake as the morning progresses. Using caffeine to speed up the process simply increases your tolerance to it. One exception may be if you have to get up really early in the morning.
  • Avoid caffeinated products for a few hours before bedtime. Because caffeine acts as a stimulant, it can make falling asleep and staying asleep more difficult.
  • Be aware that caffeine usually gets into your system within 20 to 30 minutes and the noticeable effects last approximately 4 to 6 hours.
  • Be aware of how much caffeine is in different foods and drinks (see table below).
  • If you do drink caffeinated drinks, increase your water intake to counter caffeine’s diuretic effect. You may have noticed that you need to urinate more frequently when you drink caffeinated drinks.

Most importantly, be strategic: the less caffeine you drink, the more effective it will be when you need to use it to help you stay awake.

Level of caffeine in common substances

Coffee (250 ml)

  • Instant 65-100 mg
  • Drip 115-175 mg
  • Brewed 80-135 mg
  • Espresso 100 mg

Caffeinated beverages (250 ml)

  • Coke 50 mg
  • Jolt 100 mg
  • Red Bull 80 mg

Tea (250 ml)

  • Green tea 8-30 mg
  • Normal 50-70 mg

Most chocolate bars

  • Approximately 20-40 mg

NoDoz, 1 regular strength tablet

  • 100 mg


Review your caffeine intake. Are there any changes you could make to the way you use caffeine on the job?



checkmark Knowledge Check

  • Why does caffeine loses its ability to improve your alertness if you drink caffeinated drinks regularly?
  • Name three tips you can apply to get the maximum benefit from caffeine as a stimulant.
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