Does caffeine improve reaction time?
The short answer
Yes — caffeine reliably improves reaction time, with most studies finding a 10–15ms reduction in simple visual RT at a dose of 100–300mg. The effect is real, well-replicated, and dose-dependent.
The data
| Variable | Detail |
|---|---|
| Optimal dose | 100–200mg (1–2 cups of coffee) |
| Time to peak effect | 45–60 minutes post-consumption |
| RT improvement | ~10–15ms reduction in simple RT |
| Effect in habitual users | Reduced — tolerance develops within ~7 days |
| Best time to test | 45–90 min after 1–2 cups, after ≥2 days no caffeine |
What it means for you
The mechanism: caffeine blocks adenosine receptors in the brain, which normally promote drowsiness. This increases dopamine and norepinephrine activity, boosting alertness and reducing the "noise" in neural signal transmission. Sleep-deprived subjects show the largest RT improvements from caffeine — it partially reverses the ~50ms slowing caused by poor sleep.
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Quick Answer
Yes, modestly. 100–200mg of caffeine reduces simple RT by ~10ms on average. The effect is stronger in non-habitual users and peaks ~45 minutes after consumption.
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