How Caffeine Affects Reaction Time
A small, well-measured boost — with a fast cliff.
TL;DR — Caffeine reliably improves visual reaction by 15–35 ms at moderate doses (100–200 mg), peaking 30–60 minutes after intake. Above 300 mg the gain is cancelled by hand tremor and missed cues.
Caffeine works on the adenosine system — it does not add energy, it removes the brake. That is why the boost peaks and then plateaus rather than scaling with dose.
Dose vs effect, by published studies
| Dose | Effect on simple reaction |
|---|---|
| 0 mg | Baseline |
| 50 mg | +5 to +10 ms faster |
| 100 mg | +15 to +25 ms faster |
| 200 mg | +20 to +35 ms faster |
| 300 mg | +15 to +25 ms (jitter starts) |
| 400 mg | +5 to +20 ms (variance grows) |
| 500 mg+ | Net negative for many users |
Timing the dose
Plasma caffeine peaks 30–60 minutes after oral intake on an empty stomach, 60–90 minutes after a meal. The reaction effect tracks plasma level closely. For a 20:00 esports match, finishing a 150 mg coffee by 19:00 lands you on the peak.
Tolerance and rebound
Daily users show 30–50% smaller reaction gains than occasional users at the same dose. Rebound — slower reaction the morning after — appears after habitual use of 300 mg+ per day.
What caffeine does not fix
- Sleep debt — caffeine masks symptoms but does not restore the underlying capacity.
- Dehydration — adds tremor on top of slow reaction.
- Choice latency in untrained tasks — improves only the simple-reaction component.
Frequently Asked Questions
Does coffee or pre-workout work better?
Same caffeine equals same reaction effect. Pre-workout adds beta-alanine tingles and L-theanine smoothing but no extra speed.
How long before competition?
45 minutes for empty stomach, 60–75 after a meal.
Is it worth taking on training days?
For best results, train without caffeine and use it only for measurement or competition. Otherwise tolerance erodes the effect.
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