Evidence brief · Supplement
Caffeine for Alertness / reaction time
Evidence grade A — Acute, tolerance-limited
- Overall grade
- Grade A
- Last revised
- 1
- graded outcome
- 0
- references listed
Assembled by the app from other entries in this library. It adds no evidence of its own — follow the links to the entries it draws on.
1 at grade A — 1 graded row
What is known
Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.
- Alertness / reaction timeEvidence grade A
Acute, tolerance-limited
Moderatehigh
The evidence in words
The verdict
For alertness / reaction time, Caffeine earns evidence grade A (moderate effect, high consistency) — there is real evidence here. Acute, tolerance-limited
How it might work
It blocks adenosine receptors, masking the 'sleep pressure' adenosine builds through the day, which sharpens alertness and lowers perceived exertion. Its ~5-hour half-life is why late doses wreck sleep.
How to use it
1–3 mg/kg (roughly 80–200 mg) for focus or ~3–6 mg/kg pre-exercise. Hard cutoff by early afternoon — caffeine within ~8–10 hours of bed measurably degrades sleep even when you fall asleep fine.
Safety & cautions
Safe for most in moderation; excess causes anxiety, palpitations, and insomnia. Dependence and withdrawal (headache, fatigue) are real. Combining multiple stimulants compounds cardiovascular strain.
Bottom line
A genuinely effective, cheap ergogenic and nootropic. Dose to purpose, respect the early-afternoon cutoff, and pair with theanine if it makes you jittery.
How it is used
As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.
- Focus
- 80–200 mg; theanine 200 mg to smooth it.
- Pre-exercise
- 3–6 mg/kg, ~45–60 min prior.
Goes with
- CaffeineRead the full Caffeine monographEvidence grade A
Related reading
Entries that share this one's tags or conditions.
- Caffeine for Endurance performanceEvidence grade A — Well establishedEvidence grade A
- Caffeine for Sleep (afternoon dosing)Evidence grade A — Degrades sleep — the key costEvidence grade A
- Caffeine for Strength / powerEvidence grade B — Smaller effectEvidence grade B
- Caffeine: dosage and how to take it80–200 mg; theanine 200 mg to smooth it.Evidence grade A
Sources
This entry lists no references of its own — it is assembled from the entries it links to, whose sources are on their pages.
Last revised . A grade is this entry's reading of the evidence, not medical advice.