Caffeine Side Effects

Coffee for three
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Caffeine is so common in American society you can easily forget that it is an addictive drug. People consume caffeine not only in coffee but also in tea, chocolate, and energy drinks. The latter may have much more caffeine than coffee.

While it may have some benefits, it is important to remember that you may also experience some troublesome caffeine side effects. If you experience some of these symptoms, it might be a sign that you are consuming too much caffeine.

Common Caffeine Side Effects

There are several short-term side effects that people may experience when consuming caffeine. These side effects typically occur when larger amounts of caffeine are consumed.

This often means consuming more than 400 milligrams (mg) or more than four to five cups of coffee per day. However, this can vary depending on the individual and the amount of caffeine they typically consume daily.

Research has shown that many people are unaware of these side effects, and a good deal of the research into caffeine has lauded the positive short-term effects, such as increased attention and energy, without taking these health effects into account.

According to the "Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition" (DSM-5), the tool that doctors and mental health professionals use to diagnose psychological conditions, some of the major short-term side effects of caffeine intoxication are:


Caffeine can make you feel more alert, but too much can also lead to feelings of anxiety and nervousness. Because caffeine can trigger your body's fight-or-flight response, you may be left feeling like you are on high alert. Caffeine-induced anxiety disorder is a caffeine-related condition described in the DSM-5. 


Caffeine has a stimulating effect on the bladder so it may increase the frequency and urgency of urination. One study found that consuming large quantities of caffeine (more than 450 mg per day) may increase the risk of urinary incontinence.

Flushed face

Because caffeine causes blood vessels to dilate, it can lead to flushing of the face and other areas of the body.

Gastrointestinal Disturbance

There is a range of gastrointestinal disturbances that can be side effects of too much caffeine, including stomachache, gas, heartburn, constipation, diarrhea, nausea, and vomiting. However, while stomachaches are quite common after a lot of coffee, vomiting is quite rare, and if you have this reaction, you should avoid caffeine completely until you have discussed this with your doctor.


Caffeine is one of the most common causes of headaches. It can trigger a headache when taken in excess, and if you drastically cut it out, it can cause a caffeine withdrawal headache.


People often consume caffeine to increase wakefulness, which can sometimes interfere with sleep. In some cases, people may have trouble falling asleep or may have a difficult time getting restful, restorative sleep. Caffeine may stay in your system for around five hours, so it is a good idea to stop consuming caffeine by early afternoon.

Muscle Twitching

Involuntary muscle twitches can be a side effect of caffeine for some people. However, there are other causes. If this is an ongoing problem for you, try abstaining from caffeine to see if the twitching subsides. If it does not, talk to your doctor about treatment.


After consuming caffeine, you may also find that it is difficult to relax or calm yourself down. Although this side effect may seem desirable, we all need rest. If you cannot tire enough to get adequate rest, you may not give your body adequate time to repair itself. You may not feel exhausted, but your body will become worn out without regular breaks from activity.

Caffeine can also lead to psychomotor agitation. This is a kind of physical stimulation that makes it difficult to calm your body. After consuming caffeine, people may also experience a rambling flow of thought and speech. This common side effect of stimulant drugs can make conversation and communication more difficult.

Rapid Heartbeat

Caffeine consumption can also cause tachycardia or cardiac arrhythmia. These side effects are changes to the speed and regularity of your heartbeat and cause concern. Stop using caffeine and see your doctor if you think your heartbeat is abnormal, particularly if it is excessively rapid or irregular.

Caffeine During Pregnancy

Excessive caffeine consumption during pregnancy may lead to adverse side effects. Research suggests that daily amounts over 200 mg may increase the risk of miscarriage. Some research suggests that caffeine use during pregnancy may contribute to low birth weight.

Long-Term Side Effects of Caffeine

Caffeine use or overuse may also have some long-term side effects. These can include:

Caffeine Dependence

Because this substance can be habit-forming, you may also become both physically and psychologically dependent on it. This means that if you go for a long period without any caffeine, you may begin to experience symptoms of withdrawal.

Caffeine Withdrawal

Another common long-term side effect is the experience of withdrawal symptoms. People who consume large amounts of caffeine more frequently may be more likely to feel withdrawal symptoms after several hours without a dose of caffeine. Symptoms of caffeine withdrawal can include:

  • Low mood
  • Headache
  • Nausea
  • Mental fogginess
  • Lightheadedness

Research has found that people who consume caffeine daily have a higher risk of experiencing withdrawal symptoms such as fatigue and headaches.

Positive Effects of Caffeine

Caffeine is a natural stimulant found in a number of different plant sources, most notably coffee beans, cacao seeds, and tea leaves. Because it stimulates the central nervous system (CNS), people often consume caffeine—often in the form of coffee, tea, or energy drinks—to combat tiredness and improve attention.

In addition to helping people feel more awake, research suggests that caffeine may have a number of other health benefits. These include:

  • Better memory: Some research has found that consuming caffeine may enhance memory consolidation and thus boost long-term memory.
  • Improved mood: Research has found that caffeine can have a positive effect on mood. In one study, a dose of caffeine roughly equivalent to the amount found in a single soda was associated with improvements in performance and subjective mood.
  • Increased metabolism: Studies have found that caffeine consumption can lead to increases in metabolism and may be helpful for weight maintenance.
  • Reduced mortality: One study found that consuming two to four cups of coffee per day was associated with a decreased risk of death.

Caffeine has also been found to help alleviate migraine pain in the right doses.

How to Reduce Your Caffeine Intake

According to the Food and Drug Administration (FDA), around 400 milligrams per day (which equates to about four or five cups of coffee), is safe for most adults and not associated with negative side effects. 

However, it is important to remember that individual sensitivity to caffeine's effects may vary. If you are concerned about caffeine's side effects, you might consider reducing your intake. 

Keep Track of Your Caffeine Consumption

Make note of how much caffeine you are consuming each day, whether it is in beverages, foods, or supplements. Check labels so you know whether foods or drinks contain caffeine.

Understand Your Caffeine Intake

  • 12 oz can of caffeinated soda: 30 to 40 milligrams
  • 8 oz cup of green or black tea: 30-50 milligrams
  • 8 oz cup of coffee: 80 to 100 milligrams
  • 8 oz energy drink: 40-250 milligrams

Reduce Your Intake Gradually

Quitting suddenly can lead to unpleasant withdrawal symptoms and cravings. Instead, try gradually reducing your caffeine consumption. You might drink one less cup of coffee or caffeinated soda per day. As your body adjusts to less, you can cut back more if desired.

Choose Decaffeinated Drinks

Switching to decaffeinated coffee, tea, and soda can help you cut back. If you are tapering your intake, try mixing half regular and half decaf. Brewing tea for a shorter time or switching to an herbal tea can also reduce caffeine.

Watch for Hidden Caffeine Sources

Remember that coffee isn't the only source of caffeine. If you are trying to watch your intake, you should also be aware that many foods, beverages, and supplements may also contain caffeine. Milk chocolate, dark chocolate, hot chocolate, tea, iced tea, soft drinks, energy drinks, and even decaffeinated coffee also contain varying amounts of caffeine.

A Word From Verywell

Caffeine is not harmful and can even have some benefits when consumed in moderation. However, individual responses may vary. If you are sensitive to caffeine's effects, you may want to gradually reduce your caffeine intake. You will eventually find that the unpleasant caffeine side effects you were experiencing lessen or disappear altogether.

Frequently Asked Questions

  • What are the side effects of caffeine withdrawal?

    Caffeine withdrawal can produce side effects, including headaches, fatigue, depression, irritability, nausea, muscle pain, and difficulty concentrating. Such side effects typically begin within a day and can last from a couple of days to more than a week.

  • What are the side effects of too much caffeine?

    Too much caffeine can lead to headaches, dizziness, rapid heartbeat, anxiety, insomnia, and shakiness. Excessive caffeine use may increase the risk for mood disorders, weakened bones, cancer, and heart disease.

  • How much caffeine is too much?

    The FDA suggests that for most adults, 400 mg is a safe dose that typically does not produce negative or dangerous side effects. This is the equivalent of around four of five cups of coffee per day. More than that, however, may be associated with unwanted symptoms.

  • Can too much caffeine give you a headache?

    Headaches are a common symptom of consuming too much caffeine. It is also a common symptom of caffeine withdrawal. In some cases, this may be due to a rebound effect. If you eat or drink too much caffeine, you may begin to experience withdrawal symptoms once it begins to wear off, including headaches.

  • Does coffee cause heartburn?

    Research has found that coffee can lead to problems with heartburn, indigestion, and acid reflux in some people. This is because coffee increases stomach acid, which appears to be due more to the interaction between chemical compounds in coffee and stomach acids than to the caffeine content of beverages.

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Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Elizabeth Hartney, BSc, MSc, MA, PhD
Elizabeth Hartney, BSc, MSc, MA, PhD is a psychologist, professor, and Director of the Centre for Health Leadership and Research at Royal Roads University, Canada.