Brain Health Brain Food What to Know About Caffeine Use By Elizabeth Hartney, BSc, MSc, MA, PhD 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. Learn about our editorial process Updated on July 08, 2021 Medically reviewed 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. by Steven Gans, MD Medically reviewed by Steven Gans, MD Steven Gans, MD is board-certified in psychiatry and is an active supervisor, teacher, and mentor at Massachusetts General Hospital. Learn about our Medical Review Board Fact checked Verywell Mind content is rigorously reviewed by a team of qualified and experienced fact checkers. Fact checkers review articles for factual accuracy, relevance, and timeliness. We rely on the most current and reputable sources, which are cited in the text and listed at the bottom of each article. Content is fact checked after it has been edited and before publication. Learn more. by Andrea Rice Print Jenny Dettrick / Getty Images Table of Contents View All Table of Contents What Does Caffeine Do? Common Side Effects Signs of Use Common Questions Tolerance, Dependence, & Withdrawal How to Get Help Caffeine is currently the world's most commonly used drug. It is present in many foods and drinks, which makes it is easy to forget that it is a drug. It is even an ingredient in beverages and foods that are marketed to children. While caffeine has some health benefits, it does have significant negative effects on the body and brain. Unlike many other psychoactive drugs, caffeine is legal and is one of the most widely used substances in the world. Also Known As: Because caffeine is legal, slang terms are generally not used when referring to it. Slang terms for coffee and tea, two of the most common naturally caffeinated beverages, include Joe and cuppa. Drug Class: Caffeine is classified as a stimulant. It increases activity in the central nervous system. Common Side Effects: Caffeine can increase energy levels and alertness, but side effects can include irritability, jitters, anxiety, rapid heart rate, and insomnia. How to Recognize Caffeine Caffeine is an alkaloid found in a wide variety of plants including coffee beans, tea leaves, and cocoa beans. It is found both naturally and as an additive in many food and drink items including coffee, tea, chocolate, and soft drinks. On its own, caffeine has no flavor and does not have any nutritional value. Note that while Food and Drug Administration (FDA) regulations stipulate products containing added caffeine must be labeled, labeling is not required for food and beverages that naturally contain the stimulant. Since many products do not specify how much caffeine they contain, it can be difficult to know how much caffeine you are consuming. What Does Caffeine Do? Because caffeine acts as a central nervous system (CNS) stimulant, people usually take it to feel more alert and energetic. Caffeine can improve mood and help people feel more productive. It is believed to work by blocking the neurotransmitter adenosine's receptors, increasing excitability in the brain. What the Experts Say Research has shown that caffeine can have both positive and negative effects on health. It can improve mental performance—up to a point. In a study published in 2012, caffeine was shown to improve performance on a range of different tasks including vigilance, response times, information processing, and some—but not all—proofreading tasks. But it's no shortcut to improving your performance. When comparisons are made between people whose daily intake of caffeine is low (up to 100 mg caffeine per day) and those who regularly consume a lot of caffeine (more than 300 mg caffeine per day), the improvements are quite small and don't get better with more caffeine. While people who use a lot of caffeine every day do show improved performance with more caffeine, it may be that they are simply counteracting the effects of caffeine dependence—so by taking more caffeine, they are getting closer to what their performance would be if they weren't addicted to caffeine in the first place. Caffeine might improve reaction times, but expectations may also play a role. According to a review published in 2010, caffeine improves vigilance and reaction times. Another study published in 2009 explored the subtleties of how this works and found that at least some of the time, this is an expectancy effect. Expectancy effects play a significant role in the effects that drugs have on people's perceptions and behaviors. People's expectancies of how caffeine will affect their performance—in particular, if they think it will impair their performance—seems to underlie some of these improvements. In other words, if people think consuming caffeine will make their performance worse, they try harder and compensate for the expected effects of caffeine. At recommended doses, caffeine can have a beneficial effect on mood. Caffeine influences neurotransmitters that play a role in mood and mental performance including norepinephrine, dopamine, and acetylcholine. Research published in 2013 found that drinking two to three cups of caffeinated coffee each day was linked to a lower risk of suicide. Recommendations While the FDA and other health groups have recommended limits for caffeine consumption for adults, they have not established a safe level for children. The American Academy of Pediatrics discourages caffeine use by children and adolescents. The American College of Obstetricians and Gynecologists (ACOG) recommends that pregnant women limit their caffeine intake to less than 200 mg per day. Off-Label Uses Caffeine is sometimes prescribed or used off-label to improve mental alertness in patients experiencing fatigue or drowsiness. Caffeine citrate is also used as a short-term treatment for breathing problems in premature infants. Common Side Effects Caffeine can improve alertness, but it can also lead to a number of unpleasant side effects, including: Restlessness Nervousness Excitement Insomnia Flushed FaceExcessive urinationGastrointestinal disturbances Muscle twitchingRambling speechTachycardia or cardiac arrhythmia Periods of inexhaustibility Difficulty relaxing Caffeine can also affect: Mood: While people often use caffeine to improve mood, excessive caffeine consumption can increase anxiety. Heart rate: Caffeine speeds up the heart rate with significant effects occurring after consuming 360 mg, the equivalent of about three and a half cups of brewed coffee. In higher doses, caffeine can cause more significant effects on the heart by changing the speed and regularity of your heartbeat. This is known as tachycardia or cardiac arrhythmia and can be serious. If you think your heartbeat is abnormal, check with your doctor. Blood pressure: Caffeine consumption may raise blood pressure. This effect of caffeine, known as the "pressor effect," is evident across age and gender groups, and is particularly pronounced in people with hypertension (high blood pressure). If you are unsure of whether this applies to you, ask your doctor about your blood pressure and get their advice on moderating your caffeine intake accordingly. When caffeine is consumed in large quantities, the side effects can range from unpleasant to severe, sometimes even resulting in caffeine overdose. Caffeine can also pose dangers when taken with other substances including alcohol. Caffeine use can result in excessive alcohol consumption since the stimulant effects of caffeine mask the depressant effects of alcohol. Signs of Use Since it is not an illicit drug, people rarely try to disguise their caffeine consumption. There are signs that someone might be overusing caffeine, including: Symptoms such as jitteriness, insomnia, nausea, tremors, and heart palpitationsChanges in mood including agitation or depressionExcessive consumption of caffeinated beverages Caffeine overdose can lead to symptoms such as chest pain, confusion, hallucinations, convulsions, and trouble breathing. If someone is experiencing these symptoms, contact emergency services immediately. Common Questions Some people think caffeine improves their memory. According to a review published in 2015, the research evidence for this is mixed, although a number of studies found improved memory was associated with using energy drinks. People also often wonder if excess caffeine consumption might contribute to heart problems. While caffeine use does have short-term effects on heart rate, it is unclear whether larger intakes increase the risk of cardiovascular problems in the longer term. According to a 2017 review, several studies have indicated no increased risk for cardiovascular problems in either men or women related to caffeine intake, but caffeine may be problematic for people with high blood pressure. However, if you have any type of heart disease, you should speak with your doctor before consuming any caffeinated foods and beverages. A common misconception is that caffeine use can cause infertility. A study published in 2017 suggests that there is no link between consuming low amounts of caffeine (around 200 mg per day or less) and fertility problems. Another common question is whether caffeine pills and other high-dose products are different from food and beverages containing caffeine. Products that contain high concentrations of caffeine such as pills and powders, while not chemically different from other forms of the stimulant, do pose additional dangers. Because these products are so concentrated, the difference between a safe and toxic dose is difficult to measure, which increases the risk of accidental overdose and negative side effects such as seizures. Tolerance, Dependence, and Withdrawal Repeated consumption of caffeine can lead to tolerance, dependence, and withdrawal. Tolerance takes place when you must consume larger or more frequent doses in order to have the same effects. Dependence involves needing to keep taking the substance in order to ward off unpleasant withdrawal effects. How Long Does Caffeine Stay in Your System? Caffeine reaches peak levels in the body about an hour after consumption, but you may continue to feel these stimulating effects for up to six hours. Addiction While using caffeine can lead to becoming physically or psychologically dependent on it, it does not have strong enough of an effect on the brain's reward system to result in a true addiction. The National Institute on Drug Abuse (NIDA) defines addiction as the chronic, uncontrollable use of a substance despite negative consequences. However, people often casually refer to their love of coffee and other caffeine-containing beverages as an "addiction." Caffeine Intoxication While caffeine is not considered addictive, caffeine intoxication is recognized as a disorder in the DSM-5. Caffeine intoxication is defined as the consumption of more than 250 mg of caffeine followed by at least five symptoms that can include restlessness, excitement, insomnia, diuresis, stomach upset, tachycardia, psychomotor agitation. These symptoms must result in significant distress and impairment in functioning and must not be due to another medical condition. Caffeine Addiction Symptoms and Withdrawal Withdrawal People often continue to use caffeine as a way to reduce any negative symptoms of caffeine withdrawal that they might experience. The short-term benefit you may get from caffeine can be offset by increased anxiety while you are under the influence of caffeine, and when the effects wear off, withdrawal symptoms may worsen the very mental processes you are hoping to improve. Caffeine withdrawal usually begins within 12 to 24 hours after consuming the last dose. It can lead to a number of unpleasant withdrawal effects including: Headaches Lack of energy Tremors Irritability Anxiety Fatigue and drowsiness Problems concentrating Low mood Withdrawal symptoms can range from mild to more severe depending on how much caffeine you are used to consuming. These unpleasant effects usually begin to subside within two or three days. Caffeine Withdrawal Symptoms How to Get Help If you use a lot of caffeine—drinking the equivalent of more than three cups of tea or coffee per day—it may be negatively affecting your health, so lowering your intake is worth considering. The best approach is to gradually taper your caffeine consumption. Doing this lowers your dependence gradually while minimizing the negative effects of withdrawal. It is important to be aware of all of the different sources of your intake, including foods, energy drinks, caffeine, tea, and soft drinks. Try eliminating these sources progressively by replacing them with lower-caffeine or caffeine-free alternatives. Talk to your doctor if you are concerned about your caffeine use, or contact SAMSHA at 1-800-662-4357 to find mental health services in your area. 16 Sources 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. Meredith SE, Juliano LM, Hughes JR, Griffiths RR. Caffeine use disorder: A comprehensive review and research agenda. 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Int J Health Sci (Qassim). 2015;9(4):468-474. Lyngsø J, Ramlau-Hansen CH, Bay B, Ingerslev HJ, Hulman A, Kesmodel US. Association between coffee or caffeine consumption and fecundity and fertility: a systematic review and dose-response meta-analysis. Clin Epidemiol. 2017;9:699-719. doi:10.2147/CLEP.S146496 Food and Drug Administration. Pure and highly concentrated caffeine. National Institute on Drug Abuse. Drugs, brains, and behavior: The science of addiction. 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. See Our Editorial Process Meet Our Review Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit Speak to a Therapist Online Advertiser Disclosure × The offers that appear in this table are from partnerships from which Verywell Mind receives compensation.