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Understanding Caffeine Side Effects
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.
Verywell Mind articles are reviewed by board-certified physicians and mental healthcare professionals. Medical Reviewers confirm the content is thorough and accurate, reflecting the latest evidence-based research. Content is reviewed before publication and upon substantial updates. Learn more.
John C. Umhau, MD, MPH, CPE is board-certified in addiction medicine and preventative medicine. He is the medical director at Alcohol Recovery Medicine. For over 20 years Dr. Umhau was a senior clinical investigator at the National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health (NIH).
Caffeine is so common in American society you can easily forget that it is an addictive substance. 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.
At a Glance
Caffeine can have mental health benefits, such as improving alertness, memory, mood, and even longevity. However, caffeine can also have side effects, particularly if you consume it in high doses. Let's take a closer look at some of the common negative effects of caffeine, the potential benefits, and what you can do to help manage or reduce your caffeine intake.
Symptoms of Too Much Caffeine
When caffeine intake exceeds a healthy amount, it may lead to side effects. Symptoms of too much caffeine include the following:
Headache
Caffeine is a commonly used psychostimulant, meaning it's a substance that stimulates the central nervous system. This is why many people drink coffee or caffeinated tea as a morning pick-me-up. In some cases, caffeine is used as a form of pain relief, such as in the pain medicine Excedrin, which contains aspirin, paracetamol, and caffeine. However, both consuming too much caffeine and withdrawal from caffeine can cause headaches.
Caffeine can trigger what is known as "caffeine rebound." This means that after you drink a lot of caffeine, you may experience withdrawal symptoms after the initial benefits have worn off. Overall, the National Headache Foundation says that it's fine to consume caffeine in moderation. However, it's best to avoid daily use if you are experiencing frequent headaches.
Anxiety
Caffeine may affect your mood. While moderate caffeine intake can contribute to feelings of happiness, having two to six cups of caffeine can bring on anxiety. Anxiety is a feeling of being wound-up, restless, or on edge.
A review of 57 studies measured the effects of anxiety after consuming various amounts of caffeine. Results were mixed when it came to both low and high intakes. Some research showed having up to five cups of coffee had no effect on anxiety. Other studies found feelings of tension after consuming just two or three cups.
Whether you feel anxiety at low or high levels, it could indicate that you are having too much caffeine and may want to scale back.
Trouble Sleeping
When consumed close to bedtime, caffeine may cause mild sleep disturbances at moderate and high doses. Consuming caffeine before bed can reduce the quantity and quality of sleep and make it harder to fall and stay asleep. It is recommended to not have caffeine up to six hours before bed.
Natural vs. Synthetic Caffeine: What Foods Naturally Contain Caffeine?
If you’re like most adults, you probably enjoy a cup of coffee or tea now and again. These drinks are natural sources of caffeine, the most commonly used stimulant in the world ( 1 ).
Although commonly added to many products, caffeine is found naturally in only a handful of foods and beverages.
Natural and synthetic types of caffeine tend to be very similar but can have slightly different effects on your body.
In this article, I’ll discuss the difference between natural and synthetic caffeine and review the foods and drinks most rich in natural caffeine.
Natural caffeine is the type of caffeine that is naturally found in foods like coffee, tea, and chocolate.
It works by blocking adenosine receptors in your brain. Adenosine is a neurotransmitter that relaxes your brain, making you feel tired ( 1 ).
By blocking adenosine receptors, caffeine prevents adenosine from binding to them. This keeps your brain from realizing that it’s tired, which is why caffeine is so effective at fighting off sleepiness and helping you remain more alert ( 1 ).
Caffeine and Medications
Caffeine intake may interfere with the effectiveness of medications and alter how they work. The following medications are affected by caffeine intake:
- Antidepressants
- Sedatives
- Antipsychotics
- Blood pressure drugs
- Anticoagulants
- Alzheimer's and Parkinson’s drugs
- Cancer medications
- Thyroid medications
- Antibiotics
- NSAIDs
- Migraine medications
- Estrogen
- Oxandrolone
Ask your doctor how caffeine may interact with your medications so you can avoid absorption problems.
Caffeine Can Affect How Medications Work
Caffeine may increase or decrease how much medication is absorbed. This can alter the effects of the drug. Ask your healthcare provider to learn how caffeine may interfere with your medications.
Natural caffeine and synthetic caffeine have similar effects on your body
The only recent studies I could find that researched this topic found just slight differences between the effects of natural and synthetic caffeine.
One study compared synthetic caffeine with natural caffeine sourced from green coffee beans. The natural caffeine took 45 minutes to peak in the blood, while the synthetic caffeine took 37.8 minutes ( 6 ).
In addition, there was no evidence of a quicker decline in blood caffeine concentrations when the participants consumed synthetic caffeine instead of natural caffeine.
A small, slightly older study reported similar findings. It compared the effects of two sources of natural caffeine with that of a synthetic caffeine control. The natural caffeine was sourced from either green coffee beans or a guayusa tea leaf extract ( 7 ).
The researchers found that all three types of caffeine were absorbed about as quickly, although the absorption of synthetic caffeine was slightly slower than that of the two natural types.
All three caffeine sources had similar effects on the participants’ heart rate, blood pressure, and nervous systems.
Although they have a similar chemical structure and similar effects on the body, I believe that natural and synthetic sources of caffeine have two main differences that are worth considering.
The first is that foods containing natural caffeine often offer nutrients and other beneficial compounds that foods containing synthetic caffeine usually don’t.
For instance, coffee contains magnesium, potassium, manganese, phosphorus, and several B vitamins ( 8 ).
Coffee also offers varying amounts of antioxidants, which are beneficial compounds that help protect the body from damage and disease. According to a 2013 study, coffee’s antioxidant content varies depending on the way it is roasted ( 9 ).
Soda and energy drinks, two of the main sources of added caffeine, generally lack these beneficial compounds.
