Caffeine
Improves performance, endurance above all; side effects grow with the dose
What it is
A stimulant. As a supplement it is taken as a pill or powder. It peaks in the blood within 45 minutes and has a half-life of about 4–5 hours (NIH ODS).
Benefits
Caffeine improves performance in many, but not all, studies (ISSN). The most consistent effect, moderate to large, is in aerobic endurance; for strength, sprinting and jumping the benefit is small to moderate. Response is individual: some people don't respond and some respond negatively (AIS).
Dose
ISSN and IOC: 3–6 mg/kg; per ISSN, even 2 mg/kg may work. AIS: up to 3 mg/kg, the dose (about 200 mg) at which the effect plateaus. For healthy adults EFSA considers up to 200 mg at once (about 3 mg/kg) and up to 400 mg a day safe. Doses around 9 mg/kg add no benefit and bring more side effects.
Dose by body weight
2–3 mg per kg of body weight a day, no more than 400 mg a day
| Weight | Daily dose, mg |
|---|---|
| 50 kg | 100–150 |
| 60 kg | 120–180 |
| 70 kg | 140–210 |
| 80 kg | 160–240 |
| 90 kg | 180–270 |
| 100 kg | 200–300 |
When to take it
Usually 60 minutes before exercise (ISSN); NIH ODS gives a window of 15–60 minutes. Mind your sleep: half the dose is still in the blood after about 5 hours (AIS), and 100 mg close to bedtime may already affect sleep in some adults (EFSA).
Who it's for
People doing long endurance work or team sports with sprints; it works in both trained and untrained people (ISSN). Whether being used to caffeine changes the effect is disputed: AIS sees no difference, NIH ODS cites evidence both ways.
Who can skip it
People who tolerate caffeine poorly. If you are prone to anxiety, ISSN suggests limiting or avoiding it during stressful periods when caffeine is a trigger. With evening training your sleep may suffer.
Forms
Most studies used anhydrous caffeine in capsules, which makes exact dosing simpler (ISSN). Caffeine from chewing gum is absorbed faster, while overall bioavailability is comparable to capsules. Caffeine content in coffee and pre-workout supplements varies widely: 8–9-fold differences were found in coffee from similar shops. Energy drinks and pre-workout supplements containing caffeine also improved performance.
Safety
Common side effects: rapid heartbeat, anxiety, headaches, insomnia; they grow with the dose (ISSN). Pregnancy: up to 200 mg a day (EFSA). Under 18: below 2.5 mg/kg a day (AIS); EFSA: up to 3 mg/kg. Pure caffeine powder is dangerous: a death was reported after 3 g (AIS). With illness or medicines, safe doses weren't assessed: see a doctor first.
This is a summary of public sources, not medical advice. If you have a health condition, are pregnant or take medication, talk to a doctor before taking a supplement.
Sources
- ISSN position stand: caffeine and exercise performance . ISSN, 2021.
- IOC consensus statement: dietary supplements and the high-performance athlete . IOC, 2018.
- AIS Sports Supplement Framework — Caffeine, Practitioner Fact Sheet . AIS, 2025.
- Caffeine (topic page, Scientific Opinion on the safety of caffeine) . EFSA, 2015.
- Dietary Supplements for Exercise and Athletic Performance — Health Professional Fact Sheet . NIH ODS, 2024.
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