Cognition/Performance/Weight

Caffeine

Natural stimulant found in coffee and tea that increases alertness, reduces fatigue, and enhances exercise performance in healthy adults.

score

evidence

Caution

risk

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This supplement may interact with medications, medical conditions or sensitive populations. Review safety before use.

Overview

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Safety

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Quick Take

One of the most reliable cognitive and performance enhancers, but tolerance develops and afternoon use can disrupt sleep.

Caffeine is a methylxanthine stimulant naturally present in coffee beans, tea leaves, cacao, and guarana. It works primarily by blocking adenosine receptors in the brain, reducing perceived fatigue and increasing alertness. Large bodies of randomized trials confirm it acutely improves attention, reaction time, and endurance exercise capacity. It also has a well-documented thermic effect and is the most widely consumed psychoactive substance. Those who benefit most include people with occasional fatigue, shift workers, and individuals seeking acute exercise or cognitive enhancement. Those

Potential benefits

Reduces fatigue and sleepiness

Boosts exercise performance

Improves reaction time, attention

May increase metabolic rate

May improve memory recall

May reduce Parkinson's risk

May support weight management

Protocol

Amount

100-200 mg

Frequency

Once daily, or pre-workout only

When

Morning or early afternoon; avoid within 8 hours of bedtime to prevent sleep disruption. Take with or without food.

Onset Time

Acute, within 15-45 minutes; peaks in 30-60 minutes

Who Should Consider

Healthy adults needing acute alertness

Shift workers or night-shift employees

Endurance or resistance athletes pre-workout

People with occasional daytime fatigue

Those with low habitual caffeine intake

Food Sources

Brewed coffee (~80-100 mg per 8 oz cup)
Black tea (~40-50 mg per 8 oz cup)
Green tea (~25-35 mg per 8 oz cup)
Dark chocolate (~20 mg per 1 oz serving)
Guarana seeds (~double the caffeine by weight than coffee beans)

How It Works

Caffeine competitively antagonizes adenosine A1 and A2A receptors in the central nervous system, preventing the fatigue-promoting and sedative effects of adenosine. This increases neuronal firing and releases dopamine and norepinephrine, improving alertness and reaction time.

Updated 5/19/2026