Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class and is the most commonly consumed psychoactive substance globally. It is mainly used for its eugeroic, ergogenic, or nootropic (cognitive-enhancing) properties; it is also used recreationally or in social settings. Caffeine acts by blocking the binding of adenosine at a number o
Pharmaceutical compoundClinical dataPronunciation/kæˈfiːn, ˈkæfiːn/ Other namesGuaranine
Methyltheobromine
1,3,7-Trimethylxanthine
7-methyltheophylline[1] TheineAHFS/Drugs.comMonographLicense data
- US DailyMed: Caffeine
category
- AU: A
liabilityPhysical: Low–moderate (9–30%)[2]
Psychological: Low–moderate[3]Addiction
liabilityNone[4][5]Routes of
administrationCommon: By mouth Medical: Intravenous
Uncommon: Insufflation, rectal, transdermal, topical, buccal, sublingualDrug classStimulant;
Adenosinergic;
Eugeroic;
Nootropic;
Anxiogenic;
Analeptic;
PDE inhibitor;
DiureticATC code
- N06BC01 (WHO) D11AX26 (WHO), V04CG30 (WHO)
- AU: Unscheduled
- BR: Unscheduled
- CA: Unscheduled
- DE: Unscheduled
- NZ: Unscheduled
- UK: General sales list (GSL, OTC)
- US: Unscheduled
- UN: Unscheduled
- CN: OTC
Minor: CYP2E1,[7] CYP3A4,[7]
CYP2C8,[7] CYP2C9[7]Metabolites
- Paraxanthine 84%
- Theobromine 12%
- Theophylline 4%
Infants (full term): 8 hours[7]
Infants (premature): 100 hours[7]Duration of action3–4 hours[6]ExcretionUrine (100%)Identifiers IUPAC name
- 1,3,7-Trimethyl-3,7-dihydro-1H-purine-2,6-dione
- 58-08-2
- 2519
- 407
- DB00201
- 2424
- 3G6A5W338E
- D00528
- CHEBI:27732
- ChEMBL113
- none
- CFF (PDBe, RCSB PDB)
- DTXSID0020232
- Interactive image
- CN1C=NC2=C1C(=O)N(C(=O)N2C)C
- InChI=1S/C8H10N4O2/c1-10-4-9-6-5(10)7(13)12(3)8(14)11(6)2/h4H,1-3H3
- Key:RYYVLZVUVIJVGH-UHFFFAOYSA-N
Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class and is the most commonly consumed psychoactive substance globally.[10][11] It is mainly used for its eugeroic (wakefulness promoting), ergogenic (physical performance-enhancing), or nootropic (cognitive-enhancing) properties; it is also used recreationally or in social settings.[12][13] Caffeine acts by blocking the binding of adenosine at a number of adenosine receptor types, inhibiting the centrally depressant effects of adenosine and enhancing the release of acetylcholine.[14] Caffeine has a three-dimensional structure similar to that of adenosine, which allows it to bind and block its receptors.[15] Caffeine also increases cyclic AMP levels through nonselective inhibition of phosphodiesterase, increases calcium release from intracellular stores, and antagonizes GABA receptors, although these mechanisms typically occur at concentrations beyond usual human consumption.[11][16]
Caffeine is a bitter, white crystalline purine, a methylxanthine alkaloid, and is chemically related to the adenine and guanine bases of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). It is found in the seeds, fruits, nuts, or leaves of a number of plants native to Africa, East Asia, and South America[17] and helps to protect them against herbivores and from competition by preventing the germination of nearby seeds,[18] as well as encouraging consumption by select animals such as honey bees.[19] The most common sources of caffeine for human consumption are the tea leaves of the Camellia sinensis plant and the coffee bean, the seed of the Coffea plant. Some people drink beverages containing caffeine to relieve or prevent drowsiness and to improve cognitive performance. To make these drinks, caffeine is extracted by steeping the plant product in water, a process called infusion. Caffeine-containing drinks, such as tea, coffee, and cola, are consumed globally in high volumes. In 2020, almost 10 million tonnes of coffee beans were consumed globally.[20] Caffeine is the world's most widely consumed psychoactive drug.[21][22] Unlike most other psychoactive substances, caffeine remains largely unregulated and legal in nearly all parts of the world.[23] Caffeine is seen as socially acceptable in most cultures and is encouraged in some.[vague]
Caffeine has both positive and negative health effects. It can treat and prevent the premature infant breathing disorders bronchopulmonary dysplasia of prematurity and apnea of prematurity. Caffeine citrate is on the WHO Model List of Essential Medicines.[24] It may confer a modest protective effect against some diseases,[25] including Parkinson's disease.[26] Caffeine can acutely improve reaction time and accuracy for cognitive tasks.[27] Some people experience sleep disruption or anxiety if they consume caffeine,[28][29][30] but others show little disturbance. Evidence of a risk during pregnancy is equivocal; some authorities recommend that pregnant women limit caffeine to the equivalent of two cups of coffee per day or less.[31][32] 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.[33][34][3] Tolerance develops to autonomic effects (blood pressure, heart rate, nervousness) and to alerting/vigilance benefits with regular use. Chronic exposure upregulates adenosine receptors, raising the effort threshold for allocating attention—even to mundane or previously enjoyable tasks—because habitual users operate from a lowered arousal baseline.[35][36]
Caffeine is classified by the US Food and Drug Administration (FDA) as generally recognized as safe. Lethal doses, over 10 grams per day for an adult, greatly exceed the typical dose of under 500 milligrams per day.[37] The European Food Safety Authority reported that up to 400 mg of caffeine per day (around 5.7 mg/kg of body mass per day) does not raise safety concerns for non-pregnant adults, while intakes up to 200 mg per day for pregnant and lactating women do not raise safety concerns for the fetus or the breast-fed infants.[38] A 6 ounce cup of coffee typically contains 50–175 mg of caffeine, depending on what "bean" (seed) is used (and how much), how it is roasted, and how it is prepared (e.g., drip, percolation, or espresso).[39] Thus roughly 50–100 ordinary cups of coffee would be required to reach a lethal dose. However, pure powdered caffeine, which is available as a dietary supplement, can be lethal in tablespoon-sized amounts.
Uses
Medical
See also: Caffeine citrateCaffeine is used for both prevention[40] and treatment[41] of bronchopulmonary dysplasia in premature infants. It may improve weight gain during therapy[42] and reduce the incidence of cerebral palsy as well as reduce language and cognitive delay.[43][44] On the other hand, subtle long-term side effects are possible.[45]
Caffeine is used as a primary treatment for apnea of prematurity,[46] but not prevention.[47][48] It is also used for orthostatic hypotension treatment.[49][48][50]
Some people use caffeine-containing beverages such as coffee or tea to try to treat their asthma. Evidence to support this practice is poor.[51] It appears that caffeine in low doses improves airway function in people with asthma, increasing forced expiratory volume (FEV1) by 5% to 18% for up to four hours.[52]
The addition of caffeine (100–130 mg) to commonly prescribed pain relievers such as paracetamol or ibuprofen modestly improves the proportion of people who achieve pain relief.[53]
Consumption of caffeine after abdominal surgery shortens the time to recovery of normal bowel function and shortens length of hospital stay.[54]
Caffeine was formerly used as a second-line treatment for ADHD. It is considered less effective than methylphenidate or amphetamine but more so than placebo for children with ADHD.[55][56] Children, adolescents, and adults with ADHD are more likely to consume caffeine, perhaps as a form of self-medication.[56][57]
Enhancing performance
Cognitive performanceCaffeine is a central nervous system stimulant that may reduce fatigue and drowsiness.[10] At normal doses, caffeine has variable effects on learning and memory, but it generally improves reaction time, wakefulness, concentration, and motor coordination.[58][59] The amount of caffeine needed to produce these effects varies from person to person, depending on body size and degree of tolerance.[58] The desired effects arise approximately one hour after consumption, and the desired effects of a moderate dose usually subside after about three or four hours.[6]
Caffeine can delay or prevent sleep and improves task performance during sleep deprivation.[60] Shift workers who use caffeine make fewer mistakes that could result from drowsiness.[61]
Caffeine in a dose dependent manner increases alertness in both fatigued and normal individuals.[62]
A systematic review and meta-analysis from 2014 found that concurrent caffeine and L-theanine use has synergistic psychoactive effects that promote alertness, attention, and task switching; these effects are most pronounced during the first hour post-dose.[12]
A 2025 systematic review and meta-analysis found that acute caffeine intake can improve reaction time and accuracy for cognitive tasks. Increased dosages can further improve reaction time but lead to decreases in accuracy after specific intake thresholds are reached.[27]
In habitual users, however, tolerance develops rapidly; the perceived attention and alertness boost after overnight abstinence primarily reverses mild withdrawal deficits (fatigue, reduced concentration) rather than elevating performance above a true non-dependent baseline, consistent with the withdrawal-reversal hypothesis.[63][64]
Physical performanceCaffeine is a proven ergogenic aid in humans. Caffeine improves athletic performance in aerobic (especially endurance sports) and anaerobic conditions. Moderate doses of caffeine (around 5 mg/kg)[65] can improve sprint performance,[66] cycling and running time trial performance, endurance (i.e., it delays the onset of muscle fatigue and central fatigue),[65][67][68] and cycling power output.[65] Caffeine increases basal metabolic rate in adults.[69][70][71] Caffeine ingestion prior to aerobic exercise increases fat oxidation, particularly in persons with low physical fitness.[72]
Caffeine improves muscular strength and power,[73] and may enhance muscular endurance.[74] Caffeine also enhances performance on anaerobic tests.[75] Caffeine consumption before constant load exercise is associated with reduced perceived exertion. While this effect is not present during exercise-to-exhaustion exercise, performance is significantly enhanced. This is congruent with caffeine reducing perceived exertion, because exercise-to-exhaustion should end at the same point of fatigue.[76] Caffeine also improves power output and reduces time to completion in aerobic time trials,[77] an effect positively (but not exclusively) associated with longer duration exercise.[78]
