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Caffeine Facts

Stimulant; Purine alkaloid; Adenosine A1/A2A receptor antagonist

Description

Caffeine (1,3,7-trimethylxanthine) is a naturally-occurring stimulant of the xanthine class. It works by blocking adenosine — a brain chemical that signals fatigue — keeping arousal and attention systems switched on.[1][2]

Subjective effects include wakefulness, sharper focus, mild mood lift, and increased motivation. The experience is primarily restorative — caffeine lifts performance degraded by fatigue back toward a rested baseline, rather than enhancing cognition above it.[3]

Caffeine produces low-to-moderate physical dependence, with withdrawal causing headache, fatigue, and low mood.[4] A fatal dose requires far more than beverages can deliver,[5][6] but concentrated powder products have caused fatalities at doses impossible to reach through drinks alone.[7]

Dose and durationby route · individual sensitivity varies

Oral(mg)
Threshold< 10 mgLight20 – 100 mgCommon100 – 300 mgStrong300 – 500 mgHeavy500+ mg

Starts in 10 – 30 minLasts 3 – 6 hoursAfter-effects 2 – 6 hours

Body and dependence

Acute toxicity
Low
Chronic toxicity
Low
Physical dependence
Low
Psychological dependence
Low
Withdrawal
Mild
Compulsive redosing
Low

Tolerance

Builds
Moderate
Fully resets after
10 days
Carries over to
theophylline; theobromine; paraxanthine

Effectslikely at a common dose

Perception
none likely · 3 possible
Body
Wakefulness; Stimulation; +16 possible, including Insomnia, Vasoconstriction, Headache
Thinking
none likely · 14 possible, including Compulsive redosing urge
Feeling
none likely · 4 possible, including Anxiety, Depression
Self
none likely · 5 possible, including Craving
Time
none likely · 1 possible
Awareness
Sustained attention (vicara); +1 possible

Who shouldn't take it

Absolute
Panic disorder; Neonates and infants
Relative
Uncontrolled hypertension; Cardiac arrhythmias; Generalized anxiety disorder; CYP1A2 inhibitor co-administration; Pregnancy

Combinations61 recorded

Dangerous (18)
Amphetamines; Ephedrine, Pseudoephedrine; CBD; GHB, Baclofen; GHB, GBL; Ibogaine; Local anesthetics; MAOIs; MDMA, Amphetamines; MDMA, MDA; NDRIs (Wellbutrin); NRIs; Opioids; SNRIs; SSRIs; Stimulants; Synthetic cannabinoids; Salvia, Ibogaine
Caution (30)
See full page: psychedex.org/substances/caffeine
Not graded (13)
Not listed never means safe.

Seek help immediately if

No emergency profile is recorded for this substance. Not recorded never means no risk.

988 Suicide & Crisis LifelineFireside Project: 62-FIRESIDE

Version r1 · Not medical advice

References

  1. [1]
    ^Fredholm BB, Bättig K, Holmén J, Nehlig A, Zvartau EE (1999) Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. — Pharmacological Reviews PMID:10049999
  2. [2]
    ^Fredholm BB, IJzerman AP, Jacobson KA, Linden J, Müller CE (2011) International Union of Basic and Clinical Pharmacology. LXXXI. Nomenclature and classification of adenosine receptors--an update. — Pharmacological Reviews doi:10.1124/pr.110.003285
  3. [3]
    ^Cunha RA, Agostinho PM (2010) Chronic caffeine consumption prevents memory disturbance in different animal models of memory decline. — Journal of Alzheimer's Disease doi:10.3233/jad-2010-1408
  4. [4]
    ^Rocha Cabrero F, Hamilton RJ, et al. (2026) Caffeine Withdrawal — Nutrients doi:10.3390/nu16183048
  5. [5]
    ^Kohl BA, Kaur K, Dincher N, Schumann J, Carachilo T, Komurek C (2020) Acute intentional caffeine overdose treated preemptively with hemodialysis. — American Journal of Emergency Medicine doi:10.1016/j.ajem.2019.09.018
  6. [6]
    ^Cappelletti S, Piacentino D, Sani G, Aromatario M (2014) Caffeine: Cognitive and Physical Performance Enhancer or Psychoactive Drug? — Current Neuropharmacology doi:10.2174/1570159x13666141210215655
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