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Caffeine and Reaction Time: Does Coffee Make You Faster?

Research generally finds moderate caffeine improves alertness and reaction time, especially when you're tired. The catch: too much, or too late in the day, can backfire by wrecking your sleep.

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Caffeine is the world's most widely used stimulant, and reaction time is one of the measures researchers most often use to study it.

What the research says

Reviews of the research generally find that moderate doses of caffeine improve alertness, vigilance and reaction time. The effects tend to be clearest when people are fatigued or sleep-deprived, and smaller when they're already well rested.

SituationTypical effect of moderate caffeine
Tired or sleep-deprivedClearer improvement in alertness and reaction time
Well restedSmaller or modest improvement
Very high doseJitteriness and anxiety can outweigh benefits
Late in the dayCan disrupt that night's sleep

Timing and dose

  • Caffeine's effects usually build up within about an hour of drinking it.
  • European food-safety authorities consider up to 400 mg per day safe for healthy adults (lower during pregnancy). A typical cup of brewed coffee contains roughly 80 to 100 mg, but this varies widely.
  • A sleep study found that caffeine taken even six hours before bedtime still disrupted sleep.

Test it on yourself

  1. Take three rounds of the reaction time test before your usual coffee. Note your median.
  2. Take three more rounds 45 to 60 minutes later.
  3. Repeat on several days, because a single comparison is easily swayed by chance.

Because you know whether you've had caffeine, expectation can influence the result. Look for consistent patterns rather than one-off differences.

Who should be careful

People who are sensitive to caffeine, pregnant, or have heart conditions, anxiety or sleep problems should check with a healthcare professional about safe intake. This guide is general information, not medical advice.

Frequently asked questions

Does caffeine improve reaction time?
Research generally finds moderate caffeine improves alertness and reaction time, especially when you're tired.
How long does caffeine take to affect reaction time?
Effects usually build within about 30 to 60 minutes and can last several hours.
Can too much caffeine slow you down?
High doses can cause jitteriness and anxiety, and caffeine late in the day can disrupt sleep, and both hurt performance.

Sources

  1. McLellan TM, Caldwell JA, Lieberman HR. A review of caffeine's effects on cognitive, physical and occupational performance. Neurosci Biobehav Rev. 2016;71:294–312.
  2. Smith A. Effects of caffeine on human behavior. Food Chem Toxicol. 2002;40(9):1243–1255.
  3. Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. J Clin Sleep Med. 2013;9(11):1195–1200.
  4. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the safety of caffeine. EFSA Journal. 2015;13(5):4102.

About the author:

ADR is a PUBG player who built ReactionTestTime while trying to react faster in close-range fights. ADR writes and reviews every guide and test on the site and checks each claim against published research.