Also known as: Caffeine anhydrous, 1,3,7-trimethylxanthine, Guarana extract, Dicaffeine malate
Performance & PowerStrong evidence
The most widely used stimulant in the world and among the best-evidenced ergogenic aids available. Acts primarily through adenosine receptor antagonism, with performance benefits across endurance, strength and power at roughly 3-6 mg per kilogram of bodyweight.
Typical dose
100.0–400.0 mg per day
45-60 minutes pre-training; avoid within 8 hours of bedtime
What it is
Caffeine is a methylxanthine alkaloid occurring naturally in coffee, tea, cocoa, guarana and yerba mate. It is consumed daily by a large majority of adults, making it the most widely used psychoactive substance in the world.
Supplements typically use caffeine anhydrous, which is simply caffeine with the water removed, giving a consistent and precisely dosable powder. Natural sources such as guarana deliver caffeine more slowly because it is bound within plant material, which some formulators use deliberately to smooth the onset.
Individual response varies enormously, and much of that variation is genetic. Variants in the CYP1A2 gene determine how quickly caffeine is metabolised, producing fast and slow metabolisers who experience meaningfully different durations and side effect profiles from the same dose. Adenosine receptor gene variants further influence sensitivity to its anxiogenic effects.
How it works
The primary mechanism is antagonism at adenosine receptors. Adenosine accumulates through the waking day and promotes sleepiness by binding these receptors. Caffeine occupies them without activating them, blocking that signal. Crucially, this masks fatigue rather than removing it: the adenosine continues to accumulate, which is why tiredness returns sharply as caffeine clears.
Blocking adenosine also disinhibits release of dopamine and noradrenaline, producing the alertness, mood elevation and increased arousal associated with caffeine use.
For performance specifically, caffeine reduces perceived exertion, meaning a given workload simply feels easier. It also appears to enhance motor unit recruitment and calcium handling within muscle. The once-standard explanation involving increased fat oxidation and glycogen sparing has fallen out of favour, as it does not adequately account for the observed benefits.
What the evidence shows
Caffeine has one of the largest and most consistent evidence bases in sports science. Umbrella reviews covering many meta-analyses report reliable improvements across aerobic endurance, muscular endurance, strength and power, alongside benefits to reaction time, vigilance and sustained attention.
Endurance shows the largest and most consistent effects. Strength and power benefits are real but smaller. Cognitive benefits are most pronounced in sleep-deprived or fatigued individuals, and more modest in well-rested habitual users, where a meaningful portion of the perceived boost is reversal of mild withdrawal rather than enhancement above true baseline.
Habitual intake produces tolerance to some effects, particularly the subjective stimulation, though evidence suggests the performance benefits are better preserved than users expect. Complete withdrawal before competition is not clearly necessary and reliably produces headaches and irritability.
Dosing
Performance dosing is best expressed relative to bodyweight: roughly 3-6 mg per kg, taken 45-60 minutes before exercise. For an 80 kg individual that is approximately 240-480 mg.
For general alertness, 100-200 mg is sufficient for most people. Doses above 400 mg in a single serving rarely improve outcomes and reliably increase anxiety, tremor and cardiovascular effects.
Health authorities generally consider up to 400 mg daily from all sources acceptable for most healthy adults, with 200 mg the reference figure during pregnancy. Because caffeine has a half-life of several hours, intake after mid-afternoon measurably degrades sleep quality even in people who fall asleep without difficulty.
Approximately 5 hours, ranging from 2 to 10 hours depending on CYP1A2 activity
Timing
45-60 minutes pre-training; avoid within 8 hours of bedtime
Competition status
Permitted — removed from the WADA Prohibited List in 2004, but remains on the Monitoring Programme
Category
Performance & Power
Safety and side effects
At typical intakes caffeine is well tolerated by most healthy adults. Common dose-dependent effects include jitteriness, a racing feeling, digestive upset and disrupted sleep. Regular users develop physical dependence, and stopping abruptly produces headache, fatigue and low mood for several days.
The serious safety concern is pure caffeine powder. Deaths have occurred from dosing errors with bulk anhydrous caffeine, where a teaspoon can contain a lethal quantity. This is a documented hazard rather than a theoretical one, and any product supplying loose caffeine powder should carry unambiguous measurement warnings.
Combining caffeine with other stimulants compounds its effects on the heart, and stacked pre-workout products can push total intake far higher than users realise.
Who should avoid it
Limit to 200 mg daily in pregnancy, and take care while breastfeeding. Speak to your doctor before use if your heart rhythm or blood pressure is being managed, if you are prone to feeling anxious or panicky, or if you take any regular medication — several types affect how quickly caffeine is cleared. Not recommended for under-18s.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
