stimulantEVIDENCEAUSOTC
Caffeine
aka 1,3,7-trimethylxanthine · Guaranine
The world's most widely consumed psychoactive substance. Adenosine receptor antagonist enhancing alertness and attention.
Dose range50–400mg
Half-life5h
Onset30min
Safety4/5high evidence base
Mechanism of action
Competitively blocks adenosine A1 and A2A receptors. Disinhibition increases dopamine, NE, and ACh signaling.
Benefits
Alertness and reduced fatigue
EVIDENCEAUniversally supported.
Reaction time and vigilance
EVIDENCEALieberman et al. 2002.
Synergy with L-theanine
EVIDENCEAMultiple RCTs.
Side effects
- Anxiety / jitters (high dose)commonmoderate
- Insomnia (afternoon dosing)commonmoderate
- Tolerance / dependencycommonmild
Where to buy
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