Everything You Need to Know About Caffeine

Medically Reviewed By Sade Meeks, MS, RD
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Caffeine is a natural stimulant present in various products, such as coffee, tea, and chocolate. It works by stimulating the central nervous system, which increases alertness and cognitive ability. Caffeine is present in over 60 different varieties of plants. People mostly consume it in different beverages.

This article explains what caffeine is, its uses, and why people may consume it. It also discusses the side effects of caffeine and the correct daily limit.

What is caffeine?

two people holding cups of coffee
Jeremy Pawlowski/Stocksy United

Caffeine is a naturally occurring stimulant that people all around the world use. It is often present in beverages such as coffee and tea, and the main goals of consuming caffeine are to:

  • ease drowsiness
  • reduce fatigue
  • increase activity in your brain and central nervous system
  • increase blood pressure and heart rate

The earliest caffeine consumption was from tea in around 2737 BCE by a Chinese emperor. Researchers believe that the earliest caffeine consumption from coffee was around the 9th century. In the 14th century, people began roasting coffee beans, beginning the popularity of drinking coffee.

According to the Centers for Disease Control and Prevention (CDC), around 80% of adults in the United States consume caffeine daily. This is mainly in the form of coffee or tea.

Where does it come from?

Caffeine comes from a number of natural sources, including:

  • coffee beans
  • cacao beans
  • kola nuts
  • tea leaves
  • yerba mate
  • the guarana berry

Coffee and tea are the main forms of caffeine consumption. Cold beverages such as branded Coca-Cola and energy drinks are also popular.

How does caffeine work?

Caffeine works by stimulating the brain and central nervous system to provide a feeling of alertness. Once you consume caffeine, your bloodstream absorbs it from your gut.

It takes about 15–45 minutes to take effect and lasts around 5–6 hours or more in your system.

Caffeine’s primary action is on the brain. As it crosses the blood-brain carrier, it blocks the adenosine receptors in the brain. Adenosine is a neurotransmitter that makes you feel tired throughout the day as it builds up. Therefore, caffeine consumption prevents the drowsiness that adenosine receptors cause.

Caffeine will affect everyone differently, depending on factors such as:

  • their size
  • their weight
  • their overall health
  • the amount they consume
  • their resistance and tolerability, which depend on how often they consume it

What foods and drinks contain caffeine?

People consume caffeine in the form of many different food and drink products. These include:

  • coffee, including foods containing coffee, such as tiramisu
  • tea, including green tea
  • chocolate
  • guarana, which is a food additive from a native Brazilian plant
  • chewing gum
  • energy drinks
  • medications such as cough syrups

What are the benefits of caffeine?

The main benefit of consuming caffeine is the feeling of alertness that results from it stimulating your central nervous system.

Other effects on the body include helping it get rid of excess salt and water by urinating more.

Some research has also found that caffeine consumption, particularly in the form of coffee, relates to a lower risk of health conditions such as:

Compared with people who do not drink coffee, risks were reduced by 19% if participants consumed around three cups of coffee per day.

This is not to be confused with cardiovascular-related side effects such as an increased heart rate, which can happen if you consume too much caffeine.

The above review also suggests that caffeine consumption can lower the risk of several cancers, including:

The review also found a number of benefits associated with caffeine consumption, such as:

  • a lower risk of Parkinson’s disease
  • a lower risk of gallstone disease
  • a lower risk of urinary incontinence

However, it is important to remember that caffeine does not provide the same alertness or decision-making abilities that quality sleep does. This is because sleep allows the body to slow down and engage in recovery, promoting better physical and mental health.

What are the side effects and risks of caffeine?

There are adverse effects to consider when consuming caffeine. Some are mild, but some can be more dangerous. This is because caffeine is a stimulant, meaning that it can cause a short spike in blood pressure.

Increases in heart rate and blood pressure force the heart to work harder to pump blood around the body. This increases the risk of heart attack, heart failure, and sudden cardiac arrest.

Mild side effects of caffeine

Mild adverse effects include:

  • anxiety
  • insomnia
  • facial flushing
  • dehydration
  • headaches
  • muscle tremors
  • irritability
  • agitation
  • tachycardia, or an irregular heart rate
  • an upset stomach

Serious side effects of caffeine

  • an increased heart rate
  • disorientation
  • hallucinations
  • restricted blood flow to the body

Withdrawal symptoms

If you regularly consume a lot of caffeine and then abruptly stop, you may experience withdrawal symptoms. These can include:

Try not to consume too many caffeinated foods or drinks each day, and try to stick to the 400-milligram (mg) limit. A cup of coffee usually contains up to 100 mg of caffeine.

Caffeine and energy drinks

An energy drink is a beverage that contains large amounts of sugar and caffeine. People usually consume these to help them “stay alert” or to give them energy. These drinks entered the market in the late 20th century.

They often contain other legal stimulants such as taurine. However, energy drinks can have a number of adverse effects due to the high amount of sugar and caffeine they contain. Such effects can include:

The CDC states that in 2011, 1,499 students ages 12–17 years visited the emergency room for an energy drink-related incident.

Caffeine and pregnancy

Some studies suggest that people should limit or avoid caffeine consumption during their pregnancy. Risks associated with consuming caffeine during pregnancy include:

  • a low birth weight, which increases the risks of health problems later in life
  • pregnancy loss or miscarriage
  • a high risk of childhood leukemia

According to the National Institutes of Health (NIH), pregnant people should consume no more than 200 mg of caffeine per day.

What is the daily limit for caffeine use?

For most people, it is OK to consume up to 400 mg of caffeine per day.


Caffeine is a natural stimulant present in many popular foods and beverages, such as coffee, tea, and energy drinks. The main benefits of caffeine consumption are feeling alert and boosting your energy levels.

However, consuming too much caffeine can cause a number of side effects, such as anxiety or an increase in heart rate. It is important to stay within the recommended daily allowance, which is 400 mg of caffeine per day.

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Medical Reviewer: Sade Meeks, MS, RD
Last Review Date: 2022 Jul 25
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