Caffeine: MedlinePlus

P 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
P 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.
P Most people consume caffeine from drinks. The amounts 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
P 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
P 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.
P 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
- Rapid or abnormal heart rhythm
- Dehydration
- Anxiety
- Dependency, so you need to take more of it to get the same results
P Some people are more sensitive to the effects of caffeine than others.
P Energy drinks are beverages that have added caffeine. The amount of caffeine in energy drinks can vary widely, and sometimes the labels on the drinks do not give you the actual amount of caffeine in them. Energy drinks may also contain sugars, vitamins, herbs, and supplements.
P Companies that make energy drinks claim that the drinks can increase alertness and improve physical and mental performance. This has helped make the drinks popular with American teens and young adults. There's limited data showing that energy drinks might temporarily improve alertness and physical endurance. There is not enough evidence to show that they enhance strength or power. But what we do know is that energy drinks can be dangerous because they have large amounts of caffeine. And since they have lots of sugar, they can contribute to weight gain and worsen diabetes.
P Sometimes young people mix their energy drinks with alcohol. It is dangerous to combine alcohol and caffeine. Caffeine can interfere with your ability to recognize how drunk you are, which can lead you to drink more. This also makes you more likely to make bad decisions.
P You should check with your health care provider about whether you should limit or avoid caffeine if you
- Are pregnant, since caffeine passes through the placenta to your baby
- Are breastfeeding, since a small amount of caffeine that you consume is passed along to your baby
- Have sleep disorders, including insomnia
- Have migraines or other chronic headaches
- Have anxiety
- Have GERD or ulcers
- Have fast or irregular heart rhythms
- Have high blood pressure
- Take certain medicines or supplements, including stimulants, certain antibiotics, asthma medicines, and heart medicines. Check with your health care provider about whether there might be interactions between caffeine and any medicines and supplements that you take.
- Are a child or teen. Neither should have as much caffeine as adults. Children can be especially sensitive to the effects of caffeine.
P If you have been consuming caffeine on a regular basis and then suddenly stop, you may have caffeine withdrawal. Symptoms can include
- Headaches
- Drowsiness
- Irritability
- Nausea
- Difficulty concentrating
P These symptoms usually go away after a couple of days.

