Caffeine
Cognitive · Methylxanthine / adenosine antagonist
Tier A+
What this is
Most widely used psychoactive drug. FDA and EFSA both treat up to ~400 mg/day as generally safe for most healthy non-pregnant adults, but timing is crucial: the ~5-hour half-life can disrupt sleep if taken after mid-afternoon. Tolerance builds rapidly and dose escalation is common. Pure or highly concentrated caffeine powders/liquids are a separate hazard because small measuring errors can be toxic or fatal. Pairs well with L-theanine.
Mechanism
Non-selective adenosine A1/A2A receptor antagonist; blocks tonic inhibition of wake-promoting neurons; indirectly elevates dopamine/norepinephrine; cAMP elevation via PDE inhibition at high doses
Dose & route
40-400 mg/day; caffeine naive: start 50-100 mg
Citations
- https://pubmed.ncbi.nlm.nih.gov/20182035/
- https://www.mdpi.com/2072-6643/13/10/3345
- https://pmc.ncbi.nlm.nih.gov/articles/PMC4462044/
- https://pubmed.ncbi.nlm.nih.gov/42120324/
- https://www.fda.gov/consumers/consumer-updates/spilling-beans-how-much-caffeine-too-much
- https://www.efsa.europa.eu/en/efsajournal/pub/4102
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This is an independent synthesis of published research by a non-clinician. Scores are opinions supported by citations, not prescriptions. See the full disclaimer and methodology for how this score was produced and what it does and doesn't mean.