Compound
caffeine
A trimethylxanthine in which the three methyl groups are located at positions 1, 3, and 7. A purine alkaloid that occurs naturally in tea and coffee.
Studied for
8 endpoints, 10 findings, from 7 papers — 5 of them found no effect.
- Lower-body muscular strength (pooled composite)no detected effectGrade B, Likely. Human evidence, limited replication or design limits.
- Upper-body muscular strength (pooled composite)raisesGrade B, Likely. Human evidence, limited replication or design limits.
- Adverse reaction incidence (unstandardised)lowersGrade B, Likely. Human evidence, limited replication or design limits.
- Countermovement jump heightno detected effectGrade B, Likely. Human evidence, limited replication or design limits.
- One-repetition maximum strengthraisesGrade B, Likely. Human evidence, limited replication or design limits.
Structure
Loading the model…
- Class
- Organic compound
- Formula
- C8H10N4O2
- Mass
- 194.194 g/mol
- Charge
- 0
- InChIKey
- RYYVLZVUVIJVGH-UHFFFAOYSA-N
- SMILES
- Cn1c(=O)c2c(ncn2C)n(C)c1=O
- Look it up
- ChEBIPubChemBy InChIKey
Identity from ChEBI, geometry from PubChem. Not evidence — none of it carries a grade.
What the evidence says
How to read these marks10 findings across 8 endpoints, from 7 papers, strongest first, 5 of them null.
What moved
5 findings
Decreases time-trial completion time
LikelyGrade B, Likely. Human evidence, limited replication or design limits.Finding“Both low and moderate caffeine doses significantly reduced time-trial completion time relative to placebo.”
Quoted verbatim from Dose-Response Effect of Oral Caffeine Use on Aerobic Exercise Performance: A Systematic Review and Meta-Analysis.. - Study
- meta-analysis
- Dose
- Acute pre-exercise oral anhydrous caffeine; low (3 mg/kg or less) and moderate (4-6 mg/kg) dose strata
- Population
- Healthy adults aged 18-59 years performing aerobic time-trial tests
Dose-Response Effect of Oral Caffeine Use on Aerobic Exercise Performance: A Systematic Review and Meta-Analysis.2026PMID:42356375
Increases one-repetition maximum strength
LikelyGrade B, Likely. Human evidence, limited replication or design limits.Finding“In the main meta-analysis that considered data from 6 included studies, there was a significant ergogenic effect of caffeine on 1RM strength (SMD: 0.18; 95% CI: 0.10, 0.25; p < 0.001; I2 = 0%; Figure 3).”
Quoted verbatim from Ergogenic Effects of Acute Caffeine Intake on Muscular Endurance and Muscular Strength in Women: A Meta-Analysis.. - Study
- meta-analysis
- Population
- Healthy adult women; overall meta-analysis of 6 placebo-controlled crossover trials of 1RM strength
Effect 0.18 standardised mean difference, 95% CI 0.1 to 0.25
Ergogenic Effects of Acute Caffeine Intake on Muscular Endurance and Muscular Strength in Women: A Meta-Analysis.2021PMID:34072182
Decreases adverse reaction incidence (unstandardised)
LikelyGrade B, Likely. Human evidence, limited replication or design limits.Finding“The analysis found that compared with aminophylline, infants in the caffeine group had a lower chance of developing total adverse effects (OR 0.41, 95%CI: 0.17–0.97, P = 0.042).”
Quoted verbatim from Comparative efficacy and safety of caffeine citrate and aminophylline in treating apnea of prematurity: A systematic review and meta-analysis.. - Study
- meta-analysis
- Population
- Preterm infants (<37 weeks gestation) with apnea of prematurity; caffeine citrate against an ACTIVE COMPARATOR (aminophylline), not placebo; safety outcome pooled from 4 of the 10 included studies.
Effect 0.41 odds ratio, 95% CI 0.17 to 0.97
Comparative efficacy and safety of caffeine citrate and aminophylline in treating apnea of prematurity: A systematic review and meta-analysis.2022PMID:36121807
Increases upper-body muscular strength (pooled composite)
LikelyGrade B, Likely. Human evidence, limited replication or design limits.Findingreplicated ×1“In a subgroup analysis that considered only upper-body 1RM tests, there was a significant ergogenic effect of caffeine (SMD: 0.17; 95% CI: 0.09, 0.26; p < 0.001; I2 = 0%).”
Quoted verbatim from Ergogenic Effects of Acute Caffeine Intake on Muscular Endurance and Muscular Strength in Women: A Meta-Analysis.. - Study
- meta-analysis
- Population
- Healthy adult women; subgroup analysis restricted to upper-body 1RM tests (bench press, bicep curl, lat pull-down, shoulder press, row), not the overall estimate
Effect 0.17 standardised mean difference, 95% CI 0.09 to 0.26
Ergogenic Effects of Acute Caffeine Intake on Muscular Endurance and Muscular Strength in Women: A Meta-Analysis.2021PMID:34072182
Increases upper-body muscular strength (pooled composite)
LikelyGrade B, Likely. Human evidence, limited replication or design limits.Findingreplicated ×1“A subgroup analysis indicated that caffeine significantly improves upper (SMD = 0.21; 95% CI: 0.02, 0.39; p = 0.026; Fig. 3) but not lower body strength (SMD = 0.15; 95% CI: -0.05, 0.34; p = 0.147; Fig. 4).”
Quoted verbatim from Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis.. - Study
- meta-analysis
- Dose
- Acute pre-exercise ingestion (capsule, liquid or gel), mean 4.7 mg/kg, range 0.9-6 mg/kg, 45-60 min before testing
- Population
- Healthy adolescent and young-adult participants, trained and untrained, of both sexes; UPPER-BODY SUBGROUP of the pooled 1RM maximal-strength analysis, not the overall estimate. Constituent tests: bench press, machine bench press, lat pulldown.
Effect 0.21 standardised mean difference, 95% CI 0.02 to 0.39
Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis.2018PMID:29527137
What did not
5 findings
Measured, and no effect detected. These are findings, not gaps — a trial that looked and found nothing is the most easily lost result in this field.
No detected effect on lower-body muscular strength (pooled composite)
LikelyGrade B, Likely. Human evidence, limited replication or design limits.FindingNull resultreplicated ×1“In a subgroup analysis that considered only lower-body 1RM tests, there was no significant difference between caffeine and placebo (SMD: 0.16; 95% CI: −0.03, 0.35; p = 0.109; I2 = 0%).”
Quoted verbatim from Ergogenic Effects of Acute Caffeine Intake on Muscular Endurance and Muscular Strength in Women: A Meta-Analysis.. - Study
- meta-analysis
- Population
- Healthy adult women; subgroup analysis restricted to lower-body 1RM tests (squat, leg press, knee extension), not the overall estimate
Effect 0.16 standardised mean difference, 95% CI -0.03 to 0.35
Ergogenic Effects of Acute Caffeine Intake on Muscular Endurance and Muscular Strength in Women: A Meta-Analysis.2021PMID:34072182
No detected effect on lower-body muscular strength (pooled composite)
LikelyGrade B, Likely. Human evidence, limited replication or design limits.FindingNull resultreplicated ×1“A subgroup analysis indicated that caffeine significantly improves upper (SMD = 0.21; 95% CI: 0.02, 0.39; p = 0.026; Fig. 3) but not lower body strength (SMD = 0.15; 95% CI: -0.05, 0.34; p = 0.147; Fig. 4).”
Quoted verbatim from Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis.. - Study
- meta-analysis
- Dose
- Acute pre-exercise ingestion (capsule, liquid or gel), mean 4.8 mg/kg, range 0.9-6 mg/kg, 45-60 min before testing
- Population
- Healthy adolescent and young-adult participants, trained and untrained, of both sexes; LOWER-BODY SUBGROUP of the pooled 1RM maximal-strength analysis, not the overall estimate. Constituent tests: back squat, leg press.
Effect 0.15 standardised mean difference, 95% CI -0.05 to 0.34
Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis.2018PMID:29527137
No detected effect on rating of perceived exertion
LikelyGrade B, Likely. Human evidence, limited replication or design limits.FindingNull result“As shown in C, nine studies evaluated RPE after performing an exercise protocol after caffeine supplementation, finding no effect of this supplement on RPE (SMD: 0.258, 95% CI: −0.048, 0.565; I2 0.26% p = 0.260).”
Quoted verbatim from Does Acute Caffeine Supplementation Improve Physical Performance in Female Team-Sport Athletes? Evidence from a Systematic Review and Meta-Analysis.. - Study
- meta-analysis
- Dose
- Acute oral caffeine, doses across included studies 1.3-6 mg/kg, ingested 60 min before testing
- Population
- Adult female team-sport athletes; RPE recorded after an exercise protocol, pooled across nine studies
Effect 0.258 standardised mean difference, 95% CI -0.048 to 0.565
Does Acute Caffeine Supplementation Improve Physical Performance in Female Team-Sport Athletes? Evidence from a Systematic Review and Meta-Analysis.2021PMID:34684665
No detected effect on countermovement jump height
LikelyGrade B, Likely. Human evidence, limited replication or design limits.FindingNull result“CMJ performance was not improved by caffeine supplementation (WMD = 1.17, 95%CI: –0.02 to 2.36, p = 0.05).”
Quoted verbatim from Does ergogenic effect of caffeine supplementation depend on CYP1A2 genotypes? A systematic review with meta-analysis.. - Study
- meta-analysis
- Dose
- Acute single dose, 2-6 mg/kg, ingested before the performance test
- Population
- Healthy young adults (active and sedentary), pooled across CYP1A2 genotypes; countermovement jump height in cm per the review Methods; secondary endpoint (the review primary outcome was CYP1A2 genotype)
Effect 1.17 mean difference, 95% CI -0.02 to 2.36
Does ergogenic effect of caffeine supplementation depend on CYP1A2 genotypes? A systematic review with meta-analysis.2024PMID:38158179
No detected effect on time to exhaustion
SuggestiveGrade C, Suggestive. Weak human evidence, or strong evidence in a mismatched population.FindingNull result“Time to exhaustion was not significantly influenced by CAF supplementation or menstrual cycle phase (p > 0.05).”
Quoted verbatim from Effects of Caffeine Supplementation on Cognitive Function and Neuromuscular Performance Across Menstrual Cycle Phases in Eumenorrheic Female Athletes: A Randomized, Double-Blind Placebo-Controlled Pilot Trial.. - Study
- RCT
- Participants
- 12
- Dose
- 400 mg caffeine ingested one hour before the testing session
- Population
- Trained eumenorrheic female athletes with regular menstrual cycles, tested in early follicular, late follicular and mid-luteal phases