Effects of Caffeine in the Body

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Caffeine is the go-to substance many folks rely on to get them energized and ready to tackle the day. 

Whether it’s found in a cup of morning coffee or in an energy drink, caffeine offers the shot of energy most people are looking for at the start of their day — or in the middle of it. 

We know it helps perk us up, but what are the actual effects of caffeine in the body? Some effects may surprise you. 

Caffeine Consumption at a Glance

It may not come as a surprise that coffee is one of the most widely consumed drinks in the world. In fact, according to global consumer statistics, over 166 million bags of coffee were consumed in 2020 worldwide. 

The caffeine content is the number one reason for this worldwide consumption. For many people, coffee and caffeine are synonymous terms — though decaf coffee does exist. 

In the United States, more than 90% of American adults consume caffeine in some form every day. The average amount is roughly 200 milligrams a day, which is more caffeine than can be found in two 6-ounce cups of coffee. 

You can find caffeine in coffee, tea, energy drinks, sodas, and more. Each has varying caffeine amounts, but on average:

  • One 8-ounce cup of coffee contains around 95 to 200 mg of caffeine
  • An 8-ounce cup of tea yields around 14 to 60 mg of caffeine 
  • One 8-ounce energy drink contains approximately 70 to 150 mg of caffeine 
  • One 12-ounce can of soda has about 35 to 45 mg of caffeine

Where Do We Get Caffeine

Naturally occurring, caffeine can be found in over 60 different plants, making for a wide variety of caffeinated beverages. It can be found in the leaves, seeds, and fruit of various plant species. 

Examples include certain tea leaves, coffee beans, cacao pods, kola nuts, and more. In nature, caffeine can also act as a natural pesticide, warding off insects. 

In addition to the beverages listed above, caffeine can also be found as an additive in many foods, medicines (e.g., headache medicines), and dietary supplements. Typically, these are synthetic forms of caffeine. 

​​Caffeine’s Effects in the Body

Most people are aware of some of caffeine’s effects on the body, namely its effects as a stimulant. These stimulating effects are responsible for the feelings of alertness that tend to follow the morning cup of joe.  

But what is actually happening in the body when you consume caffeine?

Caffeine and the Central Nervous System

Caffeine acts as a central nervous system (CNS) stimulant. When caffeine interacts with your brain, you get the feeling of mental sharpness, and you experience a noticeable difference in your alertness and focus. This is why it seems to “perk you up” on those sleepy mornings. 

This is one reason why it is often found within dietary and sports performance supplements (e.g., pre-workouts). It offers a boost of energy, though usually short-lived. 

Caffeine and Adenosine 

One secret behind caffeine’s energy-boosting effects is its similarity to the neurotransmitter known as adenosine. As an inhibitory neurotransmitter, adenosine slows down neural activity, which promotes feelings of drowsiness. 

Researchers believe caffeine may inhibit adenosine receptors, causing neural activity to speed up rather than slow down. 

In addition to the energy boost, research suggests that caffeine could also positively affect memory

Caffeine and the Cardiovascular System

Caffeine, with its stimulating effects, can also cause temporary high blood pressure and fast heart rate. 

Researchers believe this may be attributed to its relationship with certain hormones (e.g., adrenaline). Although this is typically a temporary effect, it is something to be aware of for those with hypertension. 

Caffeine’s relationship to heart health has always been a point of contention. For years, caffeine consumption was said to be a culprit behind irregular heartbeats or arrhythmias

Still, recent research suggests caffeine could be associated with a decreased risk of heart failure by 30 percent.

Too Much of a Good Thing?

It is clear that caffeine does have many positive effects in the body, but having too much of a good thing is possible. For one, excess use of caffeine tends to create a tolerance threshold. To gain the same effects,  two cups of coffee might turn into a full pot of coffee.

Caffeine and the Digestive System

Excess caffeine increases the amount of acid in the stomach. For some, the result could be heartburn and acid reflux. Also, the body can only store so much caffeine. 

Once the liver processes it, it is released into the urine. This is why excess doses of caffeine have been associated with frequent urination. 

Excessive amounts of caffeine use can also carry symptoms such as jittery feelings,  muscle tremors, feelings of anxiety and nervousness, restlessness, irritability, headaches, and more. 

Caffeine Consumption Recommendation

The FDA recommends no more than 400 milligrams of caffeine a day for healthy adults, which usually equates to around four to five cups of coffee. This amount is not associated with any adverse or dangerous side effects, but caffeine overdose can occur with very large amounts of caffeine. 

The exact amount of caffeine in beverages can vary, so checking labels is always essential. For example, the amount of caffeine in soft drinks is likely not the same as the amount of caffeine in a bar of dark chocolate. 

So make sure to read the label as it will be the best way to get an idea of how much caffeine you are truly ingesting. 

Bottom Line

Caffeine is one of the most popular substances in the world, consumed most commonly in coffee, teas, and energy drinks.

Caffeine is best known for providing an energy boost, the morning pick-me-up. This is due to caffeine’s effects on the body’s central nervous system. 

Although caffeine dependency can happen, caffeine poses little risk to healthy adults when consumed in moderation. But there can be too much of a good thing.

Caffeine intake should be limited to less than 400 mg a day to be on the safe side. 



Global coffee consumption, 2020/21 | Statista

Caffeine Use Disorder: A Comprehensive Review and Research Agenda | NIH

Caffeine has positive effect on memory, Johns Hopkins researchers say | John Hopkins

Association Between Coffee Intake and Incident Heart Failure Risk | AHA Journals

Spilling the Beans: How Much Caffeine is Too Much? | FDA

Healthy Directions Staff Editor