Caffeine

Stimulant

What does Caffeine do in your body?

Blocks adenosine — a molecule that builds up while you're awake and makes you feel sleepy.

What does Caffeine do?

Blocks adenosine receptors in the brain, increasing alertness. Effects peak in 30–60 minutes; its half-life is about 3–7 hours.

Where does Caffeine act in the body?

Brain, heart, kidneys (mild diuretic effect).

Which foods contain Caffeine?

Coffee, tea, cola, energy drinks, chocolate, some medications.

How much Caffeine do adults need?

FDA: up to 400 mg/day is not generally associated with negative effects for healthy adults. Lower limits are advised in pregnancy.

What happens with too little Caffeine?

Not a requirement.

Can you get too much Caffeine?

Jitteriness, fast heart rate, poor sleep. Concentrated powders and pure liquid caffeine can be dangerous.

What does Caffeine interact with?

Late-day caffeine can disrupt sleep even if you fall asleep fine.

What is known and unknown about Caffeine?

Moderate coffee intake is associated with neutral-to-lower risk for several diseases in observational studies.

Evidence & sources

• For healthy adults, up to 400 mg of caffeine a day is not generally associated with dangerous, negative effects. Evidence: regulatory. Known: FDA consumer guidance based on scientific reviews. Unknown: Sensitivity varies widely. Source: US FDA, Spilling the Beans: How Much Caffeine Is Too Much? (2018).

Connected topics

• Brain
• Sleep & Recovery
• Hydration & Electrolytes
• The Dose Makes the Poison

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General education only, not medical advice. Drafted Oct 2026 · pending qualified expert review.