Caffeine

Source: MedlinePlus Health Topics, U.S. National Library of Medicine

Last synced 8/9/2026Status: primary verified

What is caffeine? Caffeine is a bitter substance that occurs naturally in more than 60 plants including: Coffee beans Tea leaves Kola nuts, which are used to flavor soft drink colas Cacao pods, which are used to make chocolate products There is also synthetic (man-made) caffeine, which is added to some medicines, foods, and drinks. For example, some pain relievers, cold medicines, and over-the-counter medicines for alertness contain synthetic caffeine. So do energy drinks and "energy-boosting" gums and snacks. Most people consume caffeine from drinks. The amount of caffeine in different drinks can vary a lot, but it is generally: An 8-ounce cup of coffee: 95-200 mg A 12-ounce can of cola: 35-45 mg An 8-ounce energy drink: 70-100 mg An 8-ounce cup of tea: 14-60 mg What are caffeine's effects on the body? Caffeine has many effects on your body's metabolism. It: Stimulates your central nervous system, which can make you feel more awake and give you a boost of energy Is a diuretic, meaning that it helps your body get rid of extra salt and water by urinating more Increases the release of acid in your stomach, sometimes leading to an upset stomach or heartburn May interfere with the absorption of calcium in the body Increases your blood pressure Within one hour of eating or drinking caffeine, it reaches its peak level in your blood. You may continue to feel the effects of caffeine for four to six hours. What are the side effects from too much caffeine? For most people, it is not harmful to consume up to 400mg of caffeine a day. If you do eat or drink too much caffeine, it can cause health problems, such as: Restlessness and shakiness Insomnia Headaches Dizziness Fast heart rate Dehydration Anxiety Dependency, so you need to take more of it to get the same results Some people are more sensitive to the effects of caffeine than others. What are energy drinks, and why can they be a problem? Energy drinks are beverages that have added caffeine. The amount of caffeine in energy

Educational only

This information is for general education and is not medical advice. Always talk to a licensed U.S. clinician about your situation, medications, or treatment decisions.