Caffeine sensitivity, which is different than an allergy or intolerance, is an indicator of how much caffeine someone can consume before feeling its effects.

Caffeine is a popular stimulant that impacts the central nervous system. Caffeine is produced naturally in plants that grow cocoa beans, kola nuts, coffee beans, tea leaves, and other substances.

There are varying degrees of caffeine sensitivity. One person can drink a triple-shot espresso without getting the jitters. Others experience insomnia hours after drinking a small glass of cola. Caffeine sensitivity can also fluctuate daily, based upon multiple changing factors.

While there’s no specific test which measures caffeine sensitivity, most people fall within one of three groups:

Most people have a normal sensitivity to caffeine. People in this range can take in up to 400 milligrams of caffeine daily, without experiencing adverse effects.

According to a 2011 study, around 10 percent of the population carries a gene linked to higher caffeine intake. They can have large amounts of caffeine, late in the day, and not experience side effects, such as unwanted wakefulness.

People with heightened hypersensitivity to caffeine can’t tolerate small amounts of it without experiencing negative side effects.

This isn’t the same thing as an allergy to caffeine, though. A variety of factors causes caffeine sensitivity, such as genetics and your liver’s ability to metabolize caffeine. A caffeine allergy occurs if your immune system mistakes caffeine as a harmful invader and attempts to fight it off with antibodies.

People with caffeine sensitivity experience an intense adrenaline rush when they consume it. They may feel as if they’ve had five or six cups of espresso after drinking only a few sips of regular coffee. Since people with caffeine sensitivity metabolize caffeine more slowly, their symptoms may last for several hours. Symptoms may include:

  • racing heartbeat
  • headache
  • jitters
  • nervousness or anxiousness
  • restlessness
  • insomnia

These symptoms differ from those of a caffeine allergy. Symptoms of a caffeine allergy include:

  • itchy skin
  • hives
  • swelling of the throat or tongue
  • in severe instances, difficulty breathing and anaphylaxis, a potentially dangerous condition

If you think you have caffeine sensitivity, make sure to become an avid label reader. Caffeine is an ingredient in many products, including medications and supplements.

Try writing a daily log of your food and drug intake to determine if you’re actually taking in more caffeine than you realize. Once you’ve definitively determined your intake, you may be able to more accurately pinpoint your sensitivity level.

If you continue to experience caffeine sensitivity, discuss your symptoms with your doctor. They can perform an allergy skin test to rule out a possible caffeine allergy. Your doctor might also recommend genetic testing to determine if you have a variation in any of the genes that affect metabolizing caffeine.

People with a normal sensitivity to caffeine can typically consume 200 to 400 milligrams daily without any ill effect. This is the equivalent of two to four 5-ounce cups of coffee. It isn’t recommended that people consume more than 600 milligrams daily. There are no current recommendations about caffeine intake for children or adolescents.

People who are highly sensitive to caffeine should greatly reduce or eliminate their intake completely. Some people are most comfortable if they consume no caffeine at all. Others may be able to tolerate a small amount, averaging 30 to 50 milligrams daily.

A 5-ounce cup of green tea has around 30 milligrams of caffeine. The average cup of decaffeinated coffee has 2 milligrams.

Many factors can result in caffeine sensitivity, such as gender, age, and weight. Other causes include:


Some medications and herbal supplements can increase caffeine’s effects. This includes the medication theophylline and the herbal supplements ephedrine and echinacea.

Genetics and brain chemistry

Your brain is made up of around 100 billion nerve cells, called neurons. The job of neurons is to transmit instructions within the brain and nervous system. They do this with the help of chemical neurotransmitters, such as adenosine and adrenaline.

Neurotransmitters act as a type of messenger service between neurons. They fire billions of times a day in reaction to your biological processes, movements, and thoughts. The more active your brain is, the more adenosine it produces.

As adenosine levels build up, you become more and more tired. Caffeine binds to adenosine receptors in the brain, blocking their ability to signal us when we become fatigued. It also impacts other neurotransmitters that have a stimulating, feel-good effect, such as dopamine.

According to a 2012 study, people with caffeine sensitivity have an amplified reaction to this process caused by a variation in their ADORA2A gene. People with this gene variation feel caffeine’s affects more powerfully and for longer periods of time.

Liver metabolism

Genetics may also play a role in how your liver metabolizes caffeine. People with caffeine sensitivity produce less of a liver enzyme called CYP1A2. This enzyme plays a role in how quickly your liver metabolizes caffeine. People with caffeine sensitivity take longer to process and eliminate caffeine from their system. This makes its impact more intense and last longer.

Caffeine sensitivity isn’t the same thing as caffeine allergy. Caffeine sensitivity may have a genetic link. While symptoms aren’t usually harmful, you can eliminate your symptoms by reducing or eliminating caffeine.