Alcohol And Reaction Time
A single drink already measurably slows you down — and the effect compounds with fatigue.
TL;DR — At a blood alcohol concentration of 0.05% reaction time slows by roughly 15–25 ms. At 0.08% (the legal driving limit in most countries) the slowdown is 60–120 ms — equivalent to losing a decade of neural conduction speed.
At the legal driving limit your reaction time is, on average, that of someone twenty years older. The effect is biological and unavoidable.
Dose-response in milliseconds
| BAC | Approx slowdown | Equivalent aging |
|---|---|---|
| 0.02% | +5–10 ms | ~3 years |
| 0.05% | +15–25 ms | ~8 years |
| 0.08% | +60–120 ms | ~20 years |
| 0.10% | +100–180 ms | ~30+ years |
| 0.15% | +200+ ms | severely impaired |
Why alcohol slows you down
Ethanol potentiates GABA-A receptor activity, increasing inhibitory neurotransmission across the cortex. This depresses both the decision component (longer to commit to a response) and the motor execution component (slower signal propagation through demyelinated-feeling pathways). The detection component is largely spared at moderate doses.
Compounding factors
- Sleep deprivation roughly doubles alcohol's slowdown effect.
- Repeated nights of drinking impair RT for 24–48 h after the last drink, even when sober.
- Combining alcohol with sedating antihistamines compounds the slowdown by 40–80 ms.
Recovery curve
Mean RT typically returns to baseline 6–10 hours after BAC reaches zero in healthy adults. In heavy drinkers, partial impairment persists for 24–72 hours due to acetaldehyde-related neural inflammation.
Frequently Asked Questions
Does one beer really slow my reaction time?
Yes — usually by 5–15 ms measurable. Not enough to feel, enough to test.
Does coffee reverse alcohol's effect on RT?
No. Caffeine produces alertness but does not restore motor speed.
How long until I am back to baseline?
Roughly 6–10 hours after BAC reaches zero in a healthy adult.
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