Caffeine: Dosage, Effects, and Alternatives

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Caffeine is said to stimulate the metabolism and wake you up. So, what’s the secret? Does caffeine improve physical performance? How much caffeine is too much? Get all the answers and some delicious alternatives to coffee!

What is caffeine?

“But first, coffee.” We all know the saying. It didn’t just come out of nowhere. A morning cup of joe is an important ritual for many of us in order to wake up. But why? The pharmacist and chemist Friedlieb Ferdinand Runge asked himself the same question in 1820. To decipher the effect of coffee, he examined the coffee bean and was the first to discover pure caffeine. 

Caffeine can be derived from the coffee plant, which can sound a little misleading because the substance is found not only in the black bean from which we brew our beloved morning drink, but in more than 60 plant species.

What kinds of caffeinated drinks are there?

Caffeine is the main active ingredient of filter coffee and espresso, and it’s also found in black and green tea. Additionally, many soft and energy drinks owe their pick-me-up effect to their caffeine content. 

Here’s an overview of caffeine-containing drinks and their respective concentrations:

DrinkCaffeine ConcentrationAmount / Portion
Coffee600- 1000mg/l 90-150mg / cup (150 ml) 
Tea (green or black)300 – 500mg/l 45-75mg / cup (150 ml) 
Cola160mg/l 40mg / can (250 ml) 
Energy Drink160-320mg/l 40-80mg / can (250 ml) 

Is caffeine a drug?

A lot of people would describe themselves as addicts who can’t start their days without a cappuccino (or two!). They consume caffeine in high doses regularly, which begs the question: can you really be dependent on it?

Scientists have been studying whether caffeine is indeed a drug for many years. According to the current state of research, caffeine intake in normal doses has no risk of dependence. The key argument: even in high concentrations, it has no influence on the reward system in the brain (unlike substances classified as drugs such as alcohol or nicotine). 

How does caffeine work?

It takes between 10 and 60 minutes for caffeine to enter our bloodstream, spread through the body, and stimulate the brain. 

By the way: Caffeine from coffee is absorbed by the body faster than from tea. Its effects start to show as soon as it comes into contact with stomach acid. The active ingredient contained in green tea and black tea, on the other hand, is released in the intestines. The effect sets in later, but is more steady and lasts longer. 

What happens when caffeine crosses the so-called blood-brain barrier? It stimulates the nervous system, increases heart activity, raises the pulse rate, and promotes metabolism. After a cup of coffee, your blood pressure and body temperature may rise, and blood vessels constrict in the brain and dilate in the rest of the body. The blood supply to your organs is improved.

The noticeable effects of caffeine at a glance:

  • Reduced feeling of fatigue
  • Increased concentration
  • General feeling of warmth
  • Increased urination and increased intestinal peristalsis

These are the side effects of caffeine, depending on dosage and sensitivity:

  • Restlessness
  • Tachycardia
  • Insomnia
  • Gastrointestinal discomfort

How long do caffeine’s effects last?

According to the Food and Drug Administration (FDA), the half-life of caffeine is about four to six hours. This means that if you have a beverage with 100mg of caffeine at 10 AM, 25 mg will still be active in your body at 10 PM. 

How sensitive someone is to caffeine and how quickly the body actually breaks down the substance may depend on many factors that have not yet been fully researched. Among other things, gender and age have an influence on how the amounts of caffeine you consume may affect you.

Does it really wake you up?

Once it reaches the brain, caffeine attaches itself to the adenosine receptors. Adenosine is a neurotransmitter and its production consumes a lot of energy. The more adenosine is released, the more exhausted we feel.

Caffeine blocks the adenosine receptors so the brain no longer perceives these fatigue signals, and you thus feel less lethargic. Caffeine, therefore, does not directly wake you up or increase your energy level. It merely suppresses feelings of exhaustion.

How much can you drink per day?

In doses of 1mg/kg body weight and above, caffeine can act as a mental stimulant. From 2.5mg/kg body weight onwards, an excitatory effect occurs, which accelerates breathing and stimulates circulation.

Higher doses from about 300mg may, depending on sensitivity and habituation, cause trembling of the hands and trigger nervousness and palpitations.  

According to the German Society for Nutrition, up to 350mg of caffeine per day is harmless. This equates to about three to four cups of coffee

A black mug of coffee as seen from above with latte art in a flower shape

©behindlensVeWhen do you hit lethal amounts of caffeine? Not until ten full grams. This is the caffeine content of more than 300 espressos. 

If you drink coffee, energy drinks, or other sources of caffeine regularly, you may get used to it. If people who are accustomed to several drinks a day suddenly stop, they often suffer from the side effects of caffeine withdrawal symptoms: headaches, nervousness, loss of concentration, and irritability.

Does caffeine help you lose weight?

According to the current state of research, caffeine may actually help you lose weight, as it has an influence on human fatty tissue. 

When it comes to fatty tissue, there’s a distinction between white and brown body fat. The white fat serves as a long-term energy store — that’s the cushion on our hips. The brown adipose tissue, on the other hand, is quite useful. It provides the body with energy in a very short time. When stimulated, brown fat may be an excellent support for the weight loss process.  

Researchers from the School of Medicine at the University of Nottingham found that caffeine increases the activity of the brown adipose tissue. Human studies have shown that brown body fat starts burning calories immediately after drinking any amount of caffeine. 

In moderation, a cup of coffee, whether filter or espresso (without milk and sugar, of course) won’t do any harm if you’re trying to lose weight.

Does caffeine increase athletic performance?

Many athletes swear by caffeinated drinks or caffeine pills before a workout to increase their performance. Is there anything to the hype?

Recent studies confirm an improvement in athletic performance by 2 to 16 percent after consuming caffeine. This is not much, and is hardly noticeable in the recreational fitness sector. But it’s different with competitive sports, where even minimal increases in performances may make a big difference. This applies to both endurance and strength athletes. 

In order to achieve this positive effect, the ideal dose is a caffeine intake of 5mg per kg body weight one hour before training. This corresponds to about three cups for a person weighing 70kg. 

Is caffeine a doping agent?

Because caffeine is technically a stimulant due to its effect on the nervous system, it was increasingly used for doping purposes in the 1980s. As a result, a threshold value of 12µg/ml in urine was established. This amount, however, can be reached after only about 300mg caffeine (2 cups of coffee). 

Everyone responds differently and absorbs caffeine at different rates. Since 2004, it has no longer been listed as a doping agent.

Alternatives to caffeine

Anyone who has a sensitive reaction to caffeine, but still wants to reap its stimulant benefits, can opt for other natural stimulants. Here is an overview of herbal remedies that may have a stimulating effect as either a powder or tea:

  • Chicory root
  • Carob powder
  • Maca powder
  • Peppermint tea
  • Ginseng tea 
  • Roseroot
  • Water with lemon


  • Caffeine is a stimulant found in more than 60 plants, including coffee and tea.
  • Caffeine stimulates the nervous system and metabolism, increases blood pressure and circulation, and raises body temperature. 
  • After drinking caffeine, we feel less tired and more focused.
  • Negative side effects and withdrawal symptoms from caffeine may include restlessness, insomnia, tremors, and palpitations.
  • A dose of 350mg per day is harmless – this amounts to about 3-4 cups of coffee.
  • Caffeine stimulates the brown adipose tissue, which burns calories in the body, and may therefore help you lose weight. In addition, consumed in moderation and before exercising, it can increase your performance during exercise. 

Sources for this article

We at foodspring use only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

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  • U.S. Food & Drug Administration (2018): Spilling the Beans: How Much Caffeine is Too Much?, [08.06.2020].
  • Deutsche Gesellschaft für Ernährung e.V. (2015): Richtig trinken – fit bleiben, [08.06.2020].
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