3–6 mg/kg for performance, 30–60 min beforehand. Avoid it 8–10 h before bed.
Reliably improves endurance and power.
View the study (systematic review) →Increases alertness and reduces fatigue.
View the study (systematic review) →Taken late, it worsens sleep even if you do not notice it.
View the study (systematic review) →⏱ 4 min read
Caffeine is the most widely consumed psychoactive substance on the planet and, paradoxically, one of the best scientifically studied: it is estimated that 80 percent of the world's adult population takes it regularly through coffee, tea, cocoa, cola drinks, or energy drinks, and the volume of clinical research accumulated over recent decades makes it one of the few compounds whose effects on physical, cognitive, and metabolic performance are described with an enviable precision compared with most supplements.
Its main mechanism of action is the blockade of adenosine receptors in the central nervous system, which prevents adenosine (a metabolite that accumulates with wakefulness and induces drowsiness) from exerting its inhibitory effect; this simple blockade triggers a secondary cascade of dopamine, norepinephrine, and glutamate release that explains the activating, anti-fatigue, and attention-enhancing effect that any coffee drinker recognizes intuitively.
Caffeine is probably the legal ergogenic aid with the best available evidence: doses of 3 to 6 milligrams per kilogram of body weight taken 30 to 60 minutes before exercise improve performance in endurance sports by 2 to 4 percent, in short high-intensity efforts by 5 to 10 percent, and in maximal strength tests by around 5 percent; these numbers may seem modest, but in competitive sports they are the difference between the podium and disqualification.
The mechanisms of the ergogenic effect are several: increased alertness and reduced perception of effort, greater mobilization of fatty acids (sparing muscle glycogen in long events), facilitation of voluntary muscle recruitment and, to a lesser extent, direct effects on muscle contraction and thermoregulation; the response is heterogeneous between people because the polymorphism of the CYP1A2 gene that metabolizes caffeine determines its effect and individual tolerance.
In contexts of sleep deprivation, night shifts, or tasks requiring sustained vigilance, caffeine consistently improves cognitive performance: doses of 100 to 200 milligrams restore attention to near-normal levels in people who have gone 24 hours without sleep, an indication that aerospace and military medicine have studied in depth and that has obvious civilian applications in high-risk professions.
In well-rested people the effect on cognition is subtler but measurable: it improves processing speed, sustained attention, and working memory, without much impact on complex executive functions or creative problem-solving; a moderate morning latte is a real cognitive tool, not a placebo of modern work culture.
Moderate coffee consumption (3 to 5 cups a day) is consistently associated in observational studies with lower all-cause mortality, lower incidence of type 2 diabetes, lower risk of Parkinson's disease, and lower cardiovascular mortality; these findings contradict the old advice to avoid coffee because of the transient rise in blood pressure it causes, an elevation that exists but does not translate into sustained hypertension in habitual consumers.
Negative cardiovascular effects appear mainly at very high doses (more than 400 mg daily) in people with prior arrhythmias, anxiety, uncontrolled hypertension, or pregnancy, where the recommendation is to limit intake to 200 milligrams daily or less; unfiltered coffee (French press, Turkish coffee, daily espresso) contains cafestol and kahweol, which can raise LDL cholesterol, another important nuance that filter coffee eliminates almost completely.
For physical performance, the most effective approach is a dose of 3 to 6 mg/kg taken 30 to 60 minutes before the effort, avoiding habituation if maximum acute effect is sought (some athletes do withdrawal cycles of 7-14 days before important competitions); for everyday life, keep total intake below 400 mg of caffeine (equivalent to 3-4 cups of filtered coffee) and do not take it after midday to early afternoon so as not to compromise nighttime sleep.
Caffeine taken in the 6-8 hours before sleep can significantly worsen sleep quality even if the person does not perceive difficulty falling asleep, and since sleep is one of the pillars of health, a tool that improves daytime performance at the cost of worsening rest is a bad bargain in the medium term; the timing of consumption is as important as the dose.
People with cardiac arrhythmias, clinical anxiety, sleep disorders, uncontrolled hypertension, or active peptic ulcer should moderate or avoid caffeine; pregnancy and breastfeeding require limiting it to under 200 mg daily because of effects on the fetus and infant; some drugs (quinolone antibiotics, antidepressants, anticoagulants) interact with the hepatic metabolism of caffeine and can potentiate or attenuate its effect in a clinically relevant way.
Withdrawal syndrome is real for habitual consumers: headache, fatigue, and irritability appear 12-24 hours after the last dose and last 2-9 days, which explains the almost compulsive morning ritual of many coffee drinkers and why stopping abruptly is inadvisable if you want to reduce consumption; a gradual decrease over two to three weeks is better.
Information, not medical advice. Scientific evidence reflects the quality of the studies.