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Applied topically, this ingredient works as a vasoconstrictor, antioxidant, and diuretic. However, due to its diuretic effect, may be drying as well.

Caffeine (Wikipedia)
This article is about the stimulant drug. For other uses, see Caffeine (disambiguation).
2D structure of caffeine
3D structure of caffeine
Systematic (IUPAC) name
Clinical data
Pronunciation /kæˈfn, ˈkæfn/
AHFS/ monograph
  • AU: A
  • US: C (Risk not ruled out)
Physical: low–moderate
Psychological: low
Low / None
Routes of
oral, insufflation, enema, rectal, intravenous
Legal status
Legal status
  • Unscheduled globally
Pharmacokinetic data
Bioavailability 99%
Protein binding 25–36%
Metabolism Primary: CYP1A2
Minor: CYP2E1,CYP3A4,CYP2C8,CYP2C9
Metabolites Paraxanthine (84%)
Theobromine (12%)
Theophylline (4%)
Onset of action ~1 hour
Biological half-life Adults: 3–7 hours
Neonates: 65–130 hours
Duration of action 3-4 hours
Excretion urine (100%)
CAS Number 58-08-2 YesY
ATC code N06BC01 (WHO)
PubChem CID 2519
DrugBank DB00201 YesY
ChemSpider 2424 YesY
UNII 3G6A5W338E YesY
KEGG D00528 YesY
ChEBI CHEBI:27732 YesY
Synonyms Guaranine
Chemical data
Formula C8H10N4O2
Molar mass 194.19 g/mol
Physical data
Density 1.23 g/cm3
Melting point 235 to 238 °C (455 to 460 °F) (anhydrous)
See also: data page

Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is the world's most widely consumed psychoactive drug, but — unlike many other psychoactive substances — it is legal and unregulated in nearly all parts of the world. There are several known mechanisms of action to explain the effects of caffeine. The most prominent is that it reversibly blocks the action of adenosine on its receptor and consequently prevents the onset of drowsiness induced by adenosine. Caffeine also stimulates certain portions of the autonomic nervous system.

Caffeine is a bitter, white crystalline purine, a methylxanthine alkaloid, and is closely related chemically to the adenine and guanine contained in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). It is found in the seeds, nuts, or leaves of a number of plants native to South America and East Asia and confers on them several survival and reproductive benefits. The most well known source of caffeine is the coffee bean, a misnomer for the seed of Coffea plants. Beverages containing caffeine are ingested to relieve or prevent drowsiness and to improve performance. To make these drinks, caffeine is extracted by steeping the plant product in water, a process called infusion. Caffeine-containing drinks, such as coffee, tea, and cola, are very popular; in 2005, 90% of North American adults consumed caffeine daily.

Caffeine can have both positive and negative health effects. It can be used to treat bronchopulmonary dysplasia of prematurity, and to prevent apnea of prematurity: caffeine citrate was placed on the WHO Model List of Essential Medicines in 2007. It may confer a modest protective effect against some diseases, including Parkinson's disease and certain types of cancer. One meta-analysis concluded that cardiovascular disease such as coronary artery disease and stroke is less likely with 3–5 cups of non-decaffeinated coffee per day but more likely with over 5 cups per day. Some people experience insomnia or sleep disruption if they consume caffeine, especially during the evening hours, but others show little disturbance. Evidence of a risk during pregnancy is equivocal; some authorities recommend that pregnant women limit consumption to the equivalent of two cups of coffee per day or less. Caffeine can produce a mild form of drug dependence – associated with withdrawal symptoms such as sleepiness, headache, and irritability – when an individual stops using caffeine after repeated daily intake.Tolerance to the autonomic effects of increased blood pressure and heart rate, and increased urine output, develops with chronic use (i.e., these symptoms become less pronounced or do not occur following consistent use).[citation needed]

Caffeine is classified by the Food and Drug Administration as "generally recognized as safe" (GRAS). Toxic doses, over 10 grams per day for an adult, are much higher than typical dose of under 500 milligrams per day. A cup of coffee contains 80–175 mg of caffeine, depending on what "bean" (seed) is used and how it is prepared (e.g. drip, percolation, or espresso). Thus it requires roughly 50–100 ordinary cups of coffee to reach a lethal dose. However pure powdered caffeine, which is available as a dietary supplement, can be lethal in tablespoon-sized amounts.

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