Caffeine
Methylxanthine stimulant. The most widely consumed psychoactive substance. Enhances alertness, focus, and exercise performance.
Also known as Caffeine Anhydrous, Caffeine Citrate
Common doses
100-400 mg
Best timing
Morning
Food
With or without food
Interactions
6 known
Caffeine is the world's most widely consumed psychoactive substance, found in coffee, tea, cocoa, and guarana. As a supplement, caffeine is used for alertness, exercise performance, and fat oxidation. It works primarily by blocking adenosine receptors, preventing the drowsiness signal that adenosine normally produces.
Caffeine is one of the few supplements with strong, consistent evidence for athletic performance enhancement. It improves endurance, power output, reaction time, and perceived effort across a wide range of exercise types.
Individual caffeine sensitivity varies enormously based on CYP1A2 genotype. Fast metabolisers clear caffeine quickly and tend to benefit most from its performance effects. Slow metabolisers may experience jitters, anxiety, and disrupted sleep even at moderate doses.
Key benefits
Alertness and focus
Caffeine blocks adenosine receptors, reducing drowsiness and increasing alertness. Effects begin within 15-45 minutes and last 3-5 hours.
Exercise performance
Caffeine improves endurance performance by 2-4% and strength by 3-5% at doses of 3-6 mg/kg body weight taken 30-60 minutes before exercise.
Fat oxidation
Caffeine increases lipolysis and fat oxidation during exercise. It is a common ingredient in fat-burning supplements for this reason.
Cognitive performance
Caffeine improves reaction time, vigilance, and working memory, especially under conditions of sleep deprivation.
Available forms
Caffeine Anhydrous
Pure dehydrated caffeine. Precise dosing. Found in most supplements and pre-workouts. 100-200 mg per dose is typical.
Caffeine + L-Theanine
The popular nootropic stack. L-theanine smooths caffeine's stimulant edge. 2:1 ratio (theanine:caffeine) is standard.
Sustained-Release Caffeine
Extended release for sustained energy without spikes or crashes. Useful for long workdays or endurance events.
Dicaffeine Malate
Caffeine bonded with malic acid. Marketed as gentler on the stomach. Limited research on superiority.
Food sources
- Coffee (80-100 mg per cup)
- Black tea (40-60 mg per cup)
- Green tea (25-40 mg per cup)
- Dark chocolate (20-30 mg per ounce)
- Cola drinks (30-40 mg per can)
Upper intake limit
400 mg/day for healthy adults (FDA). Pregnant women should limit to 200 mg/day. Individual tolerance varies significantly based on genetics and habituation.
Research summary
One of the most evidence-backed performance supplements. Strong evidence for endurance, power, and cognitive performance. Well-characterised side effects (insomnia, anxiety, GI distress, tachycardia at high doses). The CYP1A2 genotype determines fast vs slow metabolism, which significantly affects both benefits and risks.
Known interactions (6)
Guarana is caffeine — risk of double-dosing
Two stimulants with dangerous cardiovascular synergy
Coffee polyphenols sharply reduce iron absorption
High caffeine intake modestly increases calcium loss
Caffeine does not negate creatine's benefits
The most studied nootropic combination
Check your full stack
for interactions.
See what competes, what combines well, and when to take everything. Every interaction cites a published source.
Stack
6 supplements
Stack review
1 flagZinc and Iron compete for the same absorption pathway. Take at least 2 hours apart.
Supplements
This information is for educational purposes only. It is not medical advice and does not diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional.