Nootropic profile
Caffeine
The world's most widely consumed psychoactive substance, caffeine enhances alertness, attention, and cognitive performance through adenosine receptor antagonism. Well-studied with robust evidence for focus, reaction time, and mental energy at low to moderate doses.
Best for
Educational only: this is not medical advice. Always check with a qualified healthcare professional before starting any supplement.
What is Caffeine?
Caffeine is a central nervous system stimulant belonging to the methylxanthine class.
What it does for you
Community and editorial ratings, out of 5:
How to take it
- Low Dose: 40–100 mg for mild alertness with minimal side effects.
- Moderate Dose: 100–300 mg for reliable improvements in reaction time, accuracy, and vigilance.
- Upper Limit: 400 mg/day is the generally safe limit for adults.
Watch out for
- GRAS Status: Recognised as safe up to 400 mg/day for healthy adults. Pregnant women should limit to 200 mg/day.
- Common Side Effects: Restlessness, insomnia, increased heart rate, jitteriness, anxiety - especially above 400 mg.
- Sleep Disruption: Reduces total sleep time by ~45 minutes and suppresses melatonin secretion.
- Dependence: Regular use leads to physical dependence. Withdrawal symptoms (headache, fatigue) last 2–9 days.
- Toxicity: Toxic effects at ~1.2 g. Estimated lethal dose is 10–14 g.
The science, if you're curious.
- Blocks A1 and A2A adenosine receptors, preventing adenosine from exerting its sleep-promoting and neurally inhibitory effects.
- Indirectly increases dopaminergic signalling in the prefrontal cortex and nucleus accumbens, supporting motivation and mood.
- Activates noradrenergic neurons in the locus coeruleus, enhancing arousal and sustained attention.
- Facilitates cholinergic transmission through A1 receptor blockade.
Where to find it
- Coffee: 80–100 mg per cup. The most common source worldwide.
- Tea: 30–50 mg per cup. Contains L-theanine for calmer alertness.
- Guarana: 2–8% caffeine by weight with slower sustained release.
- Caffeine Anhydrous: Concentrated supplement form in tablets (100–200 mg).
- Caffeine + L-Theanine: Popular nootropic combination (100 mg caffeine + 200 mg L-theanine).
The research
L-theanine, a natural constituent in tea, and its effect on mental state
Nobre AC, Rao A, Owen GN - Asia Pacific Journal of Clinical Nutrition
L-theanine promotes relaxation and improves attention when combined with caffeine, without causing drowsiness.
Improved cognitive performance in human volunteers following administration of guarana (Paullinia cupana) extract: comparison and interaction with Panax ginseng
Kennedy DO, Haskell CF, Wesnes KA, Scholey AB - Pharmacology Biochemistry and Behavior
Caffeine significantly improved attention, speed, and accuracy, with enhanced effects when combined with theanine.
Frequently asked
The world's most widely consumed psychoactive substance, caffeine enhances alertness, attention, and cognitive performance through adenosine receptor antagonism. Well-studied with robust evidence for focus, reaction time, and mental energy at low to moderate doses.
The main benefits people report from Caffeine are: Cognitive Enhancement, Energy, Focus, Longevity, Memory, Mood, Motivation.
Low Dose: 40–100 mg for mild alertness with minimal side effects.Moderate Dose: 100–300 mg for reliable improvements in reaction time, accuracy, and vigilance.Upper Limit: 400 mg/day is the generally safe limit for adults.
GRAS Status: Recognised as safe up to 400 mg/day for healthy adults. Pregnant women should limit to 200 mg/day.Common Side Effects: Restlessness, insomnia, increased heart rate, jitteriness, anxiety - especially above 400 mg.Sleep Disruption: Reduces total sleep time by ~45 minutes and suppresses me...
Blocks A1 and A2A adenosine receptors, preventing adenosine from exerting its sleep-promoting and neurally inhibitory effects.Indirectly increases dopaminergic signalling in the prefrontal cortex and nucleus accumbens, supporting motivation and mood.Activates noradrenergic neurons in the locus coeru...
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