Caffeine is a psychoactive substance that occurs naturally in coffee. Manufacturers also include it in many sodas and energy drinks. While it is a socially acceptable substance, research is conflicting about its safety and long term impact.

A 2019 study of university students found that people who consume caffeine have a mean intake of around 173 milligrams per day (mg/day).

This is moderate caffeine intake. According to many studies, moderate intake can promote a variety of health benefits, including a lower risk of certain cancers, brain conditions, and liver problems.

However, caffeine consumptions carries several risks. Drinking too much can also lead to adverse effects.

In this article, we analyze the potential health benefits and adverse side effects of caffeine consumption.

Caffeine is a natural stimulant

a woman drinking a drink with caffeine out of a mug.Share on Pinterest
Caffeine can help counteract tiredness.

Caffeine acts as a stimulant by activating the central nervous system (CNS). It can counteract tiredness and improve concentration and focus.

Outside of coffee, people commonly consume caffeine through tea, soft drinks — particularly energy drinks — and chocolate. It is also an ingredient in some prescription and non-prescription drugs, such as cold, allergy, and pain medication.

As well as its stimulating effects, caffeine may provide several health benefits.

A 2019 review of existing literature found that consuming a moderate amount of caffeine has a protective effect against liver cancer.

In the same year, a different review of 40 studies found that drinking 2–4 cups of coffee every day had links to a reduced risk of death from all causes.

Some studies have associated caffeine consumption with positive effects on the brain.

In 2013, a study published in World Journal of Biological Psychiatry suggested that drinking between 2–4 cups of coffee a day may reduce suicide risk in adults.

More recent research in Nature journal found that consuming caffeine may boost long term memory.

Other studies have also suggested that caffeine intake may protect against type 2 diabetes, Parkinson's disease, cardiovascular disease, and stroke.

However, Steven E. Meredith, a postdoctoral research fellow at The Johns Hopkins University School of Medicine, told Medical News Today that many people forget that caffeine is a psychoactive substance. This may be due to widespread consumption.

Caffeine crosses the blood-brain barrier to stimulate the CNS.

He said:

"Unlike most other psychoactive substances, caffeine use is socially acceptable, and the drug is widely used. In fact, caffeine is the most commonly used psychoactive substance in the world.

Moreover, the vast majority of caffeine consumers use the substance regularly without apparent harm. These factors likely contribute to the perspective that caffeine is a benign substance that everyone can use without suffering any negative consequences."

Here, learn more about the benefits of coffee.

However, ingesting caffeine in high doses may lead to more harmful effects on health.

A 2015 review identified several unwanted side effects of consuming more than 400 mg of caffeine per day, including:

a fast heartbeat

  • anxiety
  • agitation
  • restlessness
  • sleeping problems
  • tremors

These effects can also present when people experience caffeine withdrawal.

However, previous research has linked even moderate amounts of caffeine to adverse effects on health.

In 2013, the results of a large prospective study suggested that consuming 300 mg of caffeine a day during pregnancy may increase the risk of having a baby with low birth weight.

A more recent meta-analysis of 17 studies that involved 233,617 participants suggested that drinking 3–4 cups of coffee every day may increase the risk of a heart attack in men but not in women.

More research is necessary to confirm whether long term caffeine consumption is safe and whether it provides benefits or increases the risk of health problems.

Read more on caffeine overdose here.

However, Meredith told MNT that the effects of caffeine can vary in each individual. This may explain the mixed outcomes of research on the impact of caffeine in the body.

For example, he advised that individuals with anxiety disorders are more susceptible to the anxiety-increasing effects of caffeine.

"Caffeine can also metabolize at different rates among individuals for various reasons. For example, cigarette smokers metabolize caffeine twice as fast as nonsmokers," he added.

"However, caffeine metabolism is slower among infants, pregnant women, and individuals with liver disease. In addition, some medications slow caffeine metabolism, which may increase the risk of caffeine intoxication. But the effects of caffeine also vary simply because we're all different."

Rob M. Van Dam, adjunct associate professor of the Department of Nutrition at the Harvard School of Public Health, told MNT that the effects of caffeine depend on individual genetic characteristics and other lifestyle factors.

"Some people may have difficulty sleeping or experience tremors or stress with relatively low caffeine intakes, and it is useful to be aware of these symptoms and reduce caffeine intake if these occur."

Given the positive effects that caffeine can have as a stimulant, Meredith told MNT that this could result in caffeine addiction for some people:

"Caffeine activates many of the same behavioral and neuropharmacological mechanisms that are activated by other reinforcers, including other drugs of abuse.

And, like many other reinforcers, caffeine is associated with various positive subjective effects like increased well-being, sociability, and feelings of energy and alertness. For this reason and others, a small percentage of the population develops caffeine use disorder."

Some people could become physically dependent on caffeine. The absence or reduction of coffee consumption in these individuals resulting in caffeine withdrawal.

This can trigger a range of symptoms, such as:

  • a headache
  • tiredness
  • reduced energy and alertness
  • sleepiness
  • low mood
  • concentration problems
  • irritability

"Dependence can become so strong for some individuals that they're unable to reduce consumption despite knowledge of recurrent physical or psychological problems associated with continued use," Meredith added.

Read more on the symptoms of caffeine withdrawal here.

Meredith suggested that doctors should be discussing caffeine use with their patients to determine whether they are consuming safe levels of the stimulant.

He warned that this is particularly important for children and adolescents.

The majority of pediatricians recommend that young people should avoid caffeine consumption, as researchers do not fully understand its effects on the developing brain. Meredith explains this in the following terms:

"Notably, caffeine interferes with sleep, and sleep plays a critical role in learning. Some laboratory research suggests that caffeine interferes with sleep and learning among adolescent rodents, which, in turn, hinders normal neurological development that is noticeable into adulthood."

"Some psychologists are also concerned that a pattern of caffeine use or abuse among young people may lead to subsequent problematic drug and alcohol use."

The Food and Drug Administration (FDA) suggest that people talk to a pediatrician before introducing caffeine into a young person's diet.

Michael R. Taylor, the deputy commissioner for foods and veterinary medicine at the FDA, said:

"We're particularly concerned about children and adolescents, and the responsibility FDA and the food industry have to protect public health and respect social norms that suggest we shouldn't be marketing stimulants, such as caffeine, to our children."

Many food and drink products now contain added caffeine to enhance their stimulating effects, such as jellybeans, waffles, syrup, and chewing gum.

Studies into the effects of caffeine have produced mixed results.

While moderate consumption of caffeine is unlikely to produce harmful effects in most people, reactions to the stimulant depend on highly individual factors, such as genetics and accompanying lifestyle choices.

People should be mindful that they are consuming a psychoactive substance when they use caffeine.