Caffeine

• Alertness, attention, and reaction time
• Athletic endurance performance (3-6 mg/kg)
• Muscular strength, power, sprinting, and jumping (smaller effect)
• Migraine and tension headache relief (combined with analgesics)
• Reduced perceived exertion during exercise
• Short-term wakefulness during sleep deprivation or shift work

Caffeine is 1,3,7-trimethylxanthine, a methylxanthine alkaloid that competitively antagonizes adenosine receptors (primarily A1 and A2A subtypes) throughout the central nervous system. Adenosine accumulates in the brain across waking hours and binds these receptors to drive the perception of fatigue and the drive to sleep. By occupying the same receptor sites without activating them, caffeine blocks adenosine's drowsiness signal, producing measurable improvements in alertness, attention, reaction time, and working memory. Secondary effects cascade from this primary mechanism: dopamine and norepinephrine release increase modestly (driving the subjective reward and mild euphoria), the sympathetic nervous system activates (raising heart rate and blood pressure), and lipolysis increases (driving the modest fat-oxidation effects studied in athletic contexts). Individual response varies substantially based on CYP1A2 metabolism genetics. The CYP1A2 gene codes for the primary hepatic enzyme that clears caffeine from circulation; common polymorphisms (rs762551) divide the population into "fast metabolizers" (CYP1A2*1A/*1A) and "slow metabolizers" (carrying *1F variants). Slow metabolizers retain caffeine in circulation 3-5x longer than fast metabolizers, meaning the same 200mg coffee produces meaningfully different effects across the population. Slow metabolizers face elevated cardiovascular risk at higher daily doses, while fast metabolizers experience shorter duration of cognitive benefit. Regular use produces upregulation of adenosine receptors, contributing to tolerance and the well-documented withdrawal syndrome on abrupt cessation. Half-life in adults is typically 3-7 hours but reaches 9-11 hours in slow metabolizers, oral contraceptive users, and during pregnancy, explaining why an afternoon coffee disrupts night sleep in users who don't recognize the duration.

Caffeine timing matters more than dose for most use cases. The half-life of 3-7 hours (longer in slow metabolizers, oral contraceptive users, and during pregnancy) means an afternoon coffee can disrupt night sleep, Drake 2013 documented that 400mg caffeine consumed 6 hours before bedtime reduced sleep by approximately 1 hour even when users reported no subjective effect. The practical guidance: consume caffeine before mid-afternoon (slow metabolizers should stop before noon). For athletic performance, 3-6mg/kg (240-480mg in a 175lb adult) taken 30-60 minutes before competition reliably improves endurance and high-intensity performance. For cognitive tasks, lower doses (1-3mg/kg, 75-225mg) typically deliver the benefit with fewer side effects. Caffeine pairs reliably with L-theanine (50-200mg) for the "focus without jitters" stack, well-documented synergy in controlled trials.

Cognitive work

75-200mg (1-3mg/kg), before mid-afternoon

Athletic performance

3-6mg/kg, 30-60 min pre-event

Sleep cutoff

Stop by early afternoon; noon for slow metabolizers

L-theanine pairing

100-200mg L-theanine + 50-200mg caffeine

Onset

Capsule: 30-45 min. Coffee: 15-30 min. Gum: 10 min.

Half-life

3-7 hours (longer in pregnancy, slow metabolizers, OCP users)

Maximum daily

EFSA: 400mg/day adults; <200mg pregnancy; 3mg/kg adolescents

Withdrawal

Headache, fatigue, irritability typical 24-48 hours after cessation in regular users

• Coffee (Brewed)

  Rating: gold

  The most-studied dietary delivery vehicle, with the bulk of cardiovascular and mortality benefit evidence. Provides caffeine plus chlorogenic acids, diterpenes, and a broader polyphenol matrix that produces health effects beyond caffeine alone. Standard brewed cup delivers 80-130mg caffeine; espresso shot 65-75mg; cold brew often 200-300mg per serving (higher than users realize).

• Caffeine Anhydrous (Capsule/Tablet)

  Rating: gold

  Pure synthetic or extracted dehydrated caffeine. The form used in essentially all controlled athletic-performance trials at 3-6mg/kg precisely-dosed protocols. Cheap and standardized; lacks the polyphenol matrix of coffee. Better for precision dosing in research and pre-workout contexts.

• Green Tea

  Rating: gold

  Lower caffeine content (~25-50mg per cup) paired with natural L-theanine (~25-50mg). The endogenous caffeine+L-theanine pairing produces the focus-without-jitters profile that consumer supplement stacks attempt to replicate. Also delivers EGCG and other catechins. The healthiest broad caffeine-delivery vehicle in epidemiologic data.

• Matcha

  Rating: gold

  Whole powdered green tea, substantially higher caffeine and L-theanine per gram than steeped tea. ~70mg caffeine per typical serving. Shade-growing process elevates L-theanine while preserving the caffeine, producing the most pronounced focus-without-jitter profile of any natural caffeine source.

• Pre-Workout Combinations

  Rating: good

  Multi-ingredient stacks combining caffeine (typically 150-300mg) with beta-alanine, citrulline, creatine, B vitamins, and others. Mechanism stacking is mechanistically reasonable; quality varies enormously. The pre-workout caffeine dose alone is often substantial, verify total daily caffeine across all sources.

• Energy Drinks

  Rating: caution

  High-caffeine (typically 80-300mg per serving) carbonated beverages with sugar, taurine, B vitamins, and other additives. Caffeine delivery is reliable; the high-sugar formulations contribute to metabolic concerns at chronic consumption. The pediatric/adolescent market has been subject to substantial public health concern; AAP recommends against energy drinks in this population.

• Caffeine Gum / Lozenges

  Rating: good

  Buccal absorption produces faster onset (~10 minutes) than oral capsule (~30-45 minutes). Useful for time-critical contexts (athletic competition, emergency response). Military research (Stayup, Military Energy Gum) has driven product development.

• Dicaffeine Malate (Infinergy®)

  Rating: good

  Malic acid-buffered caffeine marketed for "extended release" and "smoother" effects. Some pharmacokinetic differences shown; clinical outcome differences are modest. Premium pricing in some pre-workout formulations.

• Guarana (Paullinia cupana)

  Rating: good

  Brazilian botanical source, guarana seeds contain ~4-8% caffeine plus theobromine and theophylline. Energy drink ingredient. Some marketing claims "smoother" release; pharmacokinetics not meaningfully different from synthetic caffeine.

• Knowledge workers and students

  Strength of evidence for this group: strong

  The bread-and-butter use case. Reliable cognitive performance benefits at 1-3mg/kg (75-200mg typical adult dose), particularly under time pressure or attention demands. Most consistent in sleep-deprived users; benefits in well-rested users smaller and more variable.

• Endurance athletes

  Strength of evidence for this group: strong

  Caffeine is among the most-evidenced ergogenic aids in sports nutrition. ISSN position stand supports 3-6mg/kg for endurance performance; effects reproducible across cycling, running, swimming, and rowing. Lower doses (1-3mg/kg) often equally effective with fewer GI side effects.

• Tactical / shift work / military

  Strength of evidence for this group: strong

  Reaction time and vigilance benefits well-documented in fatigue and sleep-deprivation contexts. Military research has driven much of the time-critical pharmacokinetic work (gum forms, optimal timing). Particularly useful for night-shift cognitive maintenance.

• Migraine sufferers

  Strength of evidence for this group: modest

  Caffeine enhances analgesic effects of acetaminophen and aspirin (the Excedrin combination) and has independent vasoconstrictor activity that can abort early migraine. Real risk of medication-overuse headache with daily use, moderation matters.

• Pregnancy

  Strength of evidence for this group: cautious

  ACOG recommends <200mg/day during pregnancy. Higher intake associated with miscarriage risk and reduced birth weight in observational studies. Caffeine half-life extends to ~9-11 hours in pregnancy (estrogen affects CYP1A2). Decaf as a partial replacement is reasonable.

• Anxiety disorders

  Strength of evidence for this group: cautious

  Caffeine reliably amplifies anxiety symptoms in users with panic disorder, generalized anxiety, or social anxiety. Common clinical practice: reduce or eliminate caffeine before evaluating anxiety treatment response. Highly individual response.

• Cardiovascular disease

  Strength of evidence for this group: cautious

  Modest blood pressure elevation (~5-10mmHg systolic acute) and heart rate increase. Most cardiovascular outcome data is reassuring at moderate intake; high intake (>400mg/day) warrants more caution. CYP1A2 slow metabolizers face elevated risk at high doses.

• Sleep-disordered users

  Strength of evidence for this group: cautious

  Caffeine consumed within 8 hours of bedtime measurably reduces sleep quality even when users report no subjective impact. Insomnia, OSA, and other sleep disorders warrant elimination as first-line behavioral intervention.

• L-Theanine

  Interaction: synergy

  The signature caffeine combination. L-theanine (100-200mg) reduces caffeine's jitter and anxiety effects while preserving cognitive enhancement. The most-replicated synergy claim in the supplement literature.

• Creatine

  Interaction: neutral

  Older trials suggested caffeine might blunt creatine effects; modern controlled studies have not reproduced this. Most current evidence is neutral to mildly synergistic for short-duration athletic performance.

• Tyrosine

  Interaction: synergy

  Tyrosine supports dopamine and norepinephrine synthesis under stress; caffeine increases release of both neurotransmitters. Stacked in some military/tactical cognitive protocols (500-2000mg tyrosine + 200-300mg caffeine).

• Sodium Bicarbonate

  Interaction: synergy

  Caffeine + bicarbonate combination shows additive benefits for high-intensity athletic performance in trained athletes. Bicarbonate buffers exercise-induced acidosis; caffeine reduces perceived effort.

• Beta-Alanine

  Interaction: synergy

  Common pre-workout stack. Beta-alanine supports muscle carnosine buffering for slightly longer-duration efforts; caffeine improves shorter-duration alertness and force production.

• SSRIs / SNRIs

  Interaction: caution

  Some SSRIs (fluvoxamine especially) inhibit CYP1A2 and dramatically increase caffeine half-life. Anxiety side effects of antidepressant can be amplified by caffeine. Individual adjustment under prescribing clinician.

• Anticoagulants

  Interaction: caution

  Caffeine has modest antiplatelet activity at high doses. Combined with warfarin or other anticoagulants, theoretical additive bleeding risk. Modest at typical caffeine consumption.

• Stimulant Medications (ADHD)

  Interaction: caution

  Additive cardiovascular and anxiety effects when combined with prescribed amphetamine or methylphenidate. Most users tolerate moderate combinations; high-dose stimulant users often reduce caffeine.

• Theophylline / Asthma Medications

  Interaction: caution

  Theophylline is structurally related to caffeine; combination produces additive effects on heart rate, blood pressure, and CNS stimulation. Coordinate with prescribing pulmonologist.

• Lithium

  Interaction: caution

  Caffeine increases lithium clearance through renal mechanism. Variable caffeine intake can produce variable lithium levels, clinical psychiatry considers caffeine intake when monitoring lithium therapy.

• MAO Inhibitors

  Interaction: avoid

  High caffeine intake combined with MAOIs (rare antidepressant class) can produce hypertensive crisis. Rare but serious interaction.

For coffee: specialty-grade arabica from reputable roasters (verify roast date within 4 weeks); third-wave cafe sourcing typically prioritizes quality. For green tea: Japanese provenance (Uji, Shizuoka, Kagoshima regions) consistently delivers higher L-theanine content. For supplements: avoid powdered bulk caffeine without precision measurement; verify total caffeine across stacked products (pre-workout + coffee + energy drink can quickly exceed safe levels). Third-party tested pre-workout formulations (Informed Sport, NSF Certified for Sport) provide athlete-safe verification. Energy drinks: read labels, caffeine content varies from 80mg to 300mg+ per can, and "caffeine from natural sources" claims may obscure synthetic content.

Research published from: Germany.

Friedrich Ferdinand Runge isolated caffeine from coffee beans in 1819 at the University of Jena, working from beans personally provided by Goethe, the foundational characterization that named the compound. Pierre Joseph Pelletier and Joseph Bienaimé Caventou independently isolated caffeine from coffee in 1821; Oudry from tea (as "theine") in 1827; the molecules were proven identical by Gerardus Mulder in 1838. Hermann Emil Fischer synthesized caffeine in 1895, winning the 1902 Nobel Prize partly for this work, which made industrial-scale caffeine production possible. Coffee's cultural integration predates the scientific characterization by centuries. Ethiopian highland origins (Kaffa region, named for the substance) gave way to Arabian cultivation (Yemen, 15th century) and the Sufi religious-spiritual coffee culture. European introduction came through Venetian trade (1645) and Constantinople (Ottoman); the first London coffeehouses opened in the 1650s, becoming centers of intellectual and political life. Lloyd's of London, Reuters news service, and the modern stock exchange all originated in 17th-century coffeehouses. Tea's independent caffeine inheritance through Chinese tea culture (Tang dynasty, 7th century) and the British East India Company's 18th-19th century industrial-scale tea trade with India and China shaped parallel global caffeine economies. The modern energy drink era began with Lipovitan-D in Japan (Taisho Pharmaceutical, 1962) and the broader functional beverage category. Red Bull launched in Austria in 1987 (adapted from the Thai Krating Daeng), entered the US in 1997, and built the modern category that now exceeds $50 billion in global sales. The 2010s saw substantial public health concern about pediatric energy drink consumption, the FDA convened panels, Sweden and several other jurisdictions banned sales to minors, and the AAP issued formal recommendations against pediatric energy drink use. Despite this concern, the category continues to grow, with caffeine-loaded "performance beverage" formats expanding rapidly through the early 2020s.

1. 1819Runge isolates caffeine from coffee beans at Jena, with beans from Goethe
2. 1827Oudry isolates "theine" from tea, later shown identical to caffeine
3. 1895Hermann Emil Fischer synthesizes caffeine; industrial production becomes possible
4. 1902Fischer wins Nobel Prize partly for caffeine and purine synthesis
5. 1962Lipovitan-D launches in Japan, modern energy drink category begins
6. 1987Red Bull launches in Austria, building the global energy drink market
7. 2000Smit and Rogers withdrawal-reversal cognitive analysis reshapes literature
8. 2004Doherty meta-analysis establishes 3-6mg/kg ergogenic dose
9. 2006Cornelis CYP1A2 cardiovascular interaction, foundational pharmacogenomics
10. 2010ISSN caffeine position stand consolidates athletic-performance evidence
11. 2013Drake 2013 demonstrates afternoon caffeine sleep disruption
12. 2017Poole BMJ umbrella review synthesizes 200+ meta-analyses
13. 2019UK Biobank analysis complicates CYP1A2 cardiovascular risk framing

• Whether the cardiovascular protective associations of coffee observed in epidemiology represent caffeine itself, the polyphenol matrix, or selection effects in cohort studies.
• Whether the CYP1A2 slow-metabolizer cardiovascular risk signal extends to moderate coffee intake or only applies at high consumption levels.
• How best to integrate caffeine timing into modern sleep medicine, current guidance based on Drake 2013 may understate the impact for slow metabolizers.
• Whether the "caffeine + L-theanine" supplement stack matches the dietary caffeine + L-theanine pairing in green tea/matcha.
• Whether genetic testing for CYP1A2 should become routine for individuals with cardiovascular risk who consume high caffeine.
• Whether energy drink categories should face stricter regulation given pediatric exposure and emergency department visits.

Universally available globally with minimal regulatory restriction. EFSA established 400mg/day for adults and 200mg/day for pregnant women as safe upper intakes. The pharmaceutical formulations (Excedrin, NoDoz, Vivarin) are OTC in most jurisdictions. Powdered/bulk caffeine sales have been restricted in the US, Canada, and EU following overdose deaths involving teaspoon-scale measurements (1 teaspoon ≈ 3g, near lethal dose). Pre-workout and energy drink categories are largely unrestricted except for pediatric marketing limitations. Decaffeinated coffee retains polyphenol benefits with <10mg caffeine per cup.

Status current as of July 2026. Regulatory positions change, sometimes quickly.

Structure

1,3,7-trimethylxanthine (methylxanthine alkaloid)

Mechanism

Adenosine receptor antagonist (A1, A2A)

Half-life

3-7 hours (adults); 9-11 hours (pregnancy, OCP users, slow metabolizers)

Ergogenic dose

3-6mg/kg (240-480mg in 175lb adult)

Cognitive dose

1-3mg/kg (75-225mg in 175lb adult)

EFSA upper safe daily

400mg adults; 200mg pregnancy

What follows is unfinished work on our side, not a finding about Caffeine. A short entry is not a safe entry.

• Cost and market. We have not documented what it sells for or who sells it.
• Supply chain. We have not mapped where it is made.
• Who uses it. We have not documented the user groups.
• What could change. No forward-looking summary yet.
• How it compares. We have not set it against the alternatives.
• Children and teenagers. We have not checked what is known about younger people.