tuneTypical Dose
100-400 mg per day
Natural Compound
Caffeine
1,3,7-Trimethylxanthine
Evidence TierAWADA NOT PROHIBITED
watchEffect Window
Onset in 15-45 minutes with a half-life of 3-6 hours (1.5-9h range depending on CYP1A2 genotype).
check_circleCompliance
WADA NOT PROHIBITED
Overview
Clinical Summary
Caffeine is a stimulant that blocks adenosine receptors and increases alertness. It is used to improve vigilance and to enhance endurance performance by lowering perceived exertion.
Strong evidence shows improved alertness, reaction time, and endurance performance, with reduced perceived effort and pain during exercise. Effects on strength and power are smaller and more variable than endurance effects, including in newer expectancy-controlled trials. Oral caffeine mouth-rinse studies also suggest a small ingestion-free ergogenic signal, though it is clearly weaker and more context dependent than standard oral dosing. Sleep disruption and anxiety can offset benefits.
Non-selective adenosine receptor antagonist (A1/A2A) that blocks drowsiness signaling, increases catecholamine release, and enhances CNS arousal. The most well-characterized psychoactive compound in pharmacology.
Outcomes
What This Is Expected To Influence
Primary Outcomes
- Improves alertness and reaction time (A-tier)
- Enhances endurance performance by 2-4% (A-tier)
- Reduces perceived fatigue and improves sustained attention (A-tier)
Secondary Outcomes
- Modest increase in fat oxidation rate (C-tier)
- Cognitive enhancement across attention and vigilance tasks (B-tier)
- Mildly increases metabolic rate
Safety
Contraindications and Interactions
Contraindications
- Anxiety disorders
- Cardiac arrhythmias
- Pregnancy (>200mg/day)
- Uncontrolled hypertension
Side effects
- Insomnia
- Anxiety/jitteriness/restlessness
- Tachycardia or palpitations
- GI upset (nausea, diarrhea, abdominal pain, reflux)
- Headache
- Increased blood pressure
- Dependency and withdrawal symptoms
- Intoxication at excessive doses
Interactions
- CYP1A2 inhibitors (e.g., fluvoxamine, ciprofloxacin) (Probable/Moderate) - can markedly increase caffeine half-life
- Lithium (Probable/Moderate) - higher habitual caffeine may increase renal lithium excretion (lower levels), while abrupt reduction may increase serum lithium concentrations
- Other stimulants/sympathomimetics incl. ephedrine (Probable/Moderate) - additive cardiovascular/CNS stimulation
- Levothyroxine (Probable/Moderate) - concurrent caffeine can reduce absorption
- Warfarin (Possible/Moderate) - response may vary. Monitor when intake changes substantially
- Iron, calcium, zinc (Possible/Moderate) - concurrent caffeine may reduce absorption
- Antiseizure medications (Possible/Moderate) - high caffeine intake may lower seizure threshold
Avoid if
- Severe anxiety disorders
- Uncontrolled cardiac arrhythmias or hypertension
- Pregnancy when intake exceeds 200mg/day
- Children and adolescents
- People using lithium or CYP1A2-interacting medications without clinician guidance
Evidence
Study-level References
caffeine-SRC-001Umbrella Review of Meta-Analyses
Sourceopen_in_newGrgic J, et al. "Wake up and smell the coffee: caffeine supplementation and exercise performance-an umbrella review of 21 published meta-analyses." Br J Sports Med. 2020.
Population: Athletes / Active Adults
Dose protocol: 3-6 mg/kg, 30-60 min pre-exercise
Key findings: Caffeine is a highly effective ergogenic aid across aerobic endurance, muscular strength, muscular endurance, power, jumping performance, and exercise speed. Strongest effects observed in aerobic endurance tasks.
Paper content
Caffeine is a highly effective ergogenic aid across aerobic endurance, muscular strength, muscular endurance, power, jumping performance, and exercise speed. Strongest effects observed in aerobic endurance tasks.
caffeine-SRC-002Position Stand / Systematic Review
Sourceopen_in_newGoldstein ER, et al. "International Society of Sports Nutrition position stand: caffeine and performance." J Int Soc Sports Nutr. 2010;7(1):5.
Population: Athletes / General adults
Dose protocol: 3-6 mg/kg body weight
Key findings: Caffeine is effective for enhancing sport performance in trained athletes when consumed in low-to-moderate doses (~3-6 mg/kg). Does not further improve performance when consumed at higher doses (≥9 mg/kg). Effective for sustained maximal endurance exercise and time-trial performance.
Paper content
Caffeine is effective for enhancing sport performance in trained athletes when consumed in low-to-moderate doses (~3-6 mg/kg). Does not further improve performance when consumed at higher doses (≥9 mg/kg). Effective for sustained maximal endurance exercise and time-trial performance.
caffeine-SRC-003Review / Meta-analysis
Sourceopen_in_newNehlig A. "Is caffeine a cognitive enhancer?" J Alzheimers Dis. 2010;20 Suppl 1:S85-94.
Population: General adults
Dose protocol: 50-400 mg acute doses
Key findings: Caffeine improves attention, vigilance, and reaction time at doses as low as 50mg. Effects on higher-order cognitive functions (memory, executive function) are less consistent and more dose-dependent. Habitual consumers may require caffeine to restore baseline rather than enhance above it.
Paper content
Caffeine improves attention, vigilance, and reaction time at doses as low as 50mg. Effects on higher-order cognitive functions (memory, executive function) are less consistent and more dose-dependent. Habitual consumers may require caffeine to restore baseline rather than enhance above it.
caffeine-SRC-004Systematic review and three-level meta-analysis.
Sourceopen_in_newDeng H, Fan X, Song T, et al. Revisiting the evidence on caffeine mouth rinse: effects on exercise and cognitive performance: a meta-analytic review. J Int Soc Sports Nutr. 2026;23(1):2638903. doi:10.1080/15502783.2026.2638903. PMID:41774525.
Population: Healthy adults from 31 studies (167 total effect sizes) on caffeine mouth rinse.
Dose protocol: Caffeine mouth rinse (brief oral exposure without ingestion) across 31 studies
Key findings: Trivial-to-small improvements in exercise performance, strongest for aerobic endurance. Cognitive effects inconsistent. Brief 5-second rinses outperformed longer durations.
Notes: Three-level meta-analysis (167 effect sizes). Demonstrates that even non-ingested oral caffeine exposure can produce small ergogenic effects, likely through oral receptor-mediated central pathways.
Paper content
This three-level meta-analysis of 31 studies (167 effect sizes) examined caffeine mouth rinse as a non-ingestion delivery method for ergogenic benefit. The analysis found trivial-to-small improvements in exercise performance, with the strongest effects during aerobic endurance activities and in fed states. Brief rinses (approximately 5 seconds) outperformed longer durations. Cognitive effects were inconsistent overall, though processing speed showed greater sensitivity than accuracy. The authors describe caffeine mouth rinse as a practical, ingestion-free strategy yielding small but context-dependent benefits, relevant for athletes who want to avoid GI effects of caffeine ingestion.
caffeine-SRC-005Randomized controlled trial with balanced-placebo design.
Sourceopen_in_newSoares EMKVK, da Cruz CJG, Ives SJ, et al. Caffeine Supplementation Increases Muscle Strength, but Not Endurance, While Both Caffeine and Its Expectation Elevate Blood Lactate. Nutrients. 2026;18(5):801. doi:10.3390/nu18050801. PMID:41829971.
Population: Young resistance-trained men.
Dose protocol: 5 mg/kg acute caffeine in balanced-placebo design
Key findings: Caffeine increased peak torque by 4% during static and slow isokinetic contractions and mean work by 4%. No effect on muscular endurance. Expectation alone elevated blood lactate.
Notes: Balanced-placebo design separates pharmacological from expectancy effects. Small sample (n=16) of trained men limits generalization.
Paper content
This balanced-placebo RCT tested whether caffeine's effects on muscle strength are pharmacological or expectancy-driven. Sixteen resistance-trained men completed four conditions combining actual versus placebo caffeine with being told they received caffeine or placebo. Caffeine at 5 mg/kg increased peak torque by 4% during static and slow isokinetic contractions and increased mean work by 4% across all speeds. However, caffeine did not improve muscular endurance. Both actual caffeine and the expectation of receiving caffeine elevated blood lactate. The study distinguishes pharmacological from psychological contributions, showing that strength gains are genuinely drug-mediated while some metabolic responses also respond to expectancy.