What caffeine is
Caffeine is a natural stimulant found in coffee, tea, cocoa, and guarana, and added to many energy and pre-workout products. In supplements it often appears as caffeine anhydrous, a dried, concentrated form. It is the most widely consumed active compound on the planet.
How caffeine works
Caffeine blocks adenosine, a molecule that builds up through the day and makes you feel sleepy. By sitting in adenosine's parking spots, caffeine keeps drowsiness at bay and lets stimulating signals run more freely. That is why a dose lifts alertness and lowers the feeling of effort during a workout.
What the human research shows
This is one of the few supplement ingredients with genuinely strong human evidence. Many controlled trials show that caffeine improves alertness, reaction time, and memory encoding, and that it raises endurance and some power and strength measures around exercise. The performance dose is well mapped, at roughly 3 mg to 6 mg per kilogram of body weight before activity.
The catch is not whether caffeine works but how you use it. A single dose lifts alertness for only an hour or two and can be followed by a slump. Regular use builds tolerance, and late doses harm sleep. We grade the evidence as high for alertness and performance, with the real skill being dose and timing.
What we still do not know
- How much genetics explain the wide differences in how people respond.
- The best strategy to keep benefits while limiting tolerance.
- Where the long-term sweet spot sits for heavy daily users.
How people take caffeine
Most people get caffeine from coffee and tea, which is fine. For a performance dose, the research points to 3 mg to 6 mg per kilogram about an hour before exercise. Keep your daily total under 400 mg, avoid late-day doses if sleep matters, and treat concentrated powders with respect. If you have a heart condition or take medication, check with your healthcare provider first.