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Caffeine

Also known as: Coffee, Caffeine tablets

The world's most widely used stimulant. Reliable for alertness and athletic performance — dose and timing matter.

Common forms: Coffee / tea · Tablets (100–200 mg) · Gum

Draft summary, not yet reviewed by a qualified health professional · Last updated 2026-11-03

Talk to a healthcare professional first

This information is for education only and is not medical advice, diagnosis, or treatment. Supplements can interact with medications and health conditions. Check with your doctor or pharmacist before starting anything, especially if you take medication, are pregnant or breastfeeding, or have a health condition. These statements have not been evaluated by the FDA; supplements are not intended to diagnose, treat, cure, or prevent any disease.

What the evidence says

Focus & alertness

AStrong evidence

Meta-analyses show caffeine improves attention and reaction time, and partly restores cognitive performance after sleep loss.

Dose used in studies
40–200 mg (about ½–2 cups of coffee)
Time to effect
15–45 minutes
Studies (2)

Endurance & performance

AStrong evidence

An umbrella review of 21 meta-analyses found caffeine consistently improves endurance performance, and to a lesser extent strength and power.

Dose used in studies
3–6 mg/kg body weight, ~60 minutes before exercise
Time to effect
30–60 minutes
Studies (2)

Safety

Common side effects

  • Insomnia if taken late
  • Jitteriness
  • Fast heart rate
  • Anxiety
  • Stomach upset

Avoid or ask your doctor first if

  • You have an anxiety disorder, heart rhythm problems, or uncontrolled high blood pressure
  • You are pregnant (limit to 200 mg/day total)

Pregnancy & breastfeeding

Use only with guidance from your prenatal care provider.

Upper limit

~400 mg/day for most healthy adults (FDA)

Medication interactions

  • majorStimulants: Additive effects with ADHD stimulants or decongestants — fast heart rate, high blood pressure.
  • moderateMAO inhibitors: May cause dangerous increases in blood pressure or heart rate.
  • moderateCertain antibiotics: Quinolones (e.g. ciprofloxacin) slow caffeine clearance, increasing side effects.
  • moderateLithium: Changing caffeine intake can alter lithium levels.

This list covers common medication classes only and is not exhaustive.

Buying tips

Look for third-party testing seals (USP Verified, NSF Certified, or Informed Choice) and match the form and dose used in studies.

Where to buy (affiliate)

Further reading