1,3,7-trimethylxanthine, a central nervous system stimulant; action may be mediated by adenosine receptors.

A methylxanthine alkaloid found in the seeds, nuts, or leaves of a number of plants native to South America and East Asia that is structurally related to adenosine and acts primarily as an adenosine receptor antagonist with psychotropic and anti-inflammatory activities. Upon ingestion, caffeine binds to adenosine receptors in the central nervous system (CNS), which inhibits adenosine binding. This inhibits the adenosine-mediated downregulation of CNS activity; thus, stimulating the activity of the medullary, vagal, vasomotor, and respiratory centers in the brain. This agent also promotes neurotransmitter release that further stimulates the CNS. The anti-inflammatory effects of caffeine are due the nonselective competitive inhibition of phosphodiesterases (PDEs). Inhibition of PDEs raises the intracellular concentration of cyclic AMP (cAMP), activates protein kinase A, and inhibits leukotriene synthesis, which leads to reduced inflammation and innate immunity.

A methylxanthine naturally occurring in some beverages and also used as a pharmacological agent. Caffeine's most notable pharmacological effect is as a central nervous system stimulant, increasing alertness and producing agitation. It also relaxes SMOOTH MUSCLE, stimulates CARDIAC MUSCLE, stimulates DIURESIS, and appears to be useful in the treatment of some types of headache. Several cellular actions of caffeine have been observed, but it is not entirely clear how each contributes to its pharmacological profile. Among the most important are inhibition of cyclic nucleotide PHOSPHODIESTERASES, antagonism of ADENOSINE RECEPTORS, and modulation of intracellular calcium handling.

A substance found in the leaves and beans of the coffee tree, in tea, yerba mate, guarana berries, and in small amounts in cocoa. It can also be made in the laboratory, and is added to some soft drinks, foods, and medicines. Caffeine increases brain activity, alertness, attention, and energy. It may also increase blood pressure, heart rate, breathing rate, and the loss of water from the body in urine.

An alkaloid stimulant having a purine double-ring structure composed of eight carbons and four nitrogen atoms with methyl groups attached to the nitrogen atoms at the 1, 3, and 7 positions and having double bonds at the carbons in positions 2 and 6.

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. 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. 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. 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. 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. 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. 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 arrhythmia (a problem with the rate or rhythm of your heartbeat).; Have high blood pressure.; Take certain medicines or supplements, including stimulants, certain antibiotics, asthma medicines, and heart medicines. Check with your health care...

Caffeine, nitrogenous organic compound of the alkaloid group, substances that have marked physiological effects. Caffeine occurs in tea, coffee, guarana, mate, kola nuts, and cacao. Pure caffeine (trimethylxanthine) occurs as a white powder or as silky needles, which melt at 238 �C (460 �F); it...