Caffeine
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Evidence Summary
Caffeine is a widely studied stimulant with significant evidence supporting its use for enhancing physical endurance, cognitive function, and metabolic processes. Research indicates its efficacy is often modulated by genetic factors and its interaction with other compounds like L-theanine.
Evidence by Condition
Caffeine enhances endurance running performance, time to exhaustion, and fat oxidation rates during exercise.
The combination of caffeine and L-theanine improves cognitive performance, alertness, and mood.
Evidence suggests potential effects of caffeine on weight loss and anthropometric measures.
Caffeine is used as a pharmacological intervention to manage sleepiness and sleep disturbances in shift workers.
Effective Doses
Specific doses mentioned in studies include 50 mg caffeine (often paired with 100 mg L-theanine).
Key Findings
- Caffeine intake improves endurance running performance and time to exhaustion (PMID: 36615805)
- The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness (PMID: 21040626)
- Caffeine chewing gum is an effective method for supplementing exercise performance (PMID: 35239468)
- Genetic susceptibility, specifically the CYP1A2 genotype, significantly influences caffeine metabolism and athletic performance (PMID: 29509641)
- Acute caffeine intake affects fat oxidation rates during fed-state exercise (PMID: 38257100)
Limitations
The effectiveness of caffeine is highly dependent on individual genetic susceptibility (CYP1A2) and the presence of co-ingested bioactive compounds.
Safety & Interactions
Individual response and metabolism are heavily influenced by genetic variations in the CYP1A2 gene (PMID: 29509641).
AI-generated summary from 80 peer-reviewed studies. Not medical advice. Always consult a healthcare provider.
Drug-Supplement Interactions
⚠️ This information is for educational purposes only and does not constitute medical advice. Always consult your healthcare provider before combining supplements with medications.
Claims vs. Evidence
| Claim Type | % of Products | Evidence Required | Status |
|---|---|---|---|
| All Other | 98% | Tier D (Unclassified) | ✅ Supported |
| Structure/Function | 93% | Tier C (DSHEA Structure/Function (no pre-approval)) | ✅ Supported |
| Nutrient | 19% | Tier D (Unknown) | ✅ Supported |
| Qualified Health | 0% | Tier B (FDA Qualified Health Claim) | ✅ Supported |
| No Claim | 0% | Tier D (No claim on label) | ✅ Supported |
Research by Topic
⚠️ FDA Safety Data
Research Evidence (82)
**Boedt et al., 2021** | Cochrane Database Syst Rev | Meta Analysis Boedt Tessy, Vanhove Anne-Catherine, ... Lie Fong Sharon. Preconception lifestyle advice for people with infertility. Cochrane Database Syst Rev. 2021-Apr-29;4(4):CD008189. doi:10.10...
**Tabrizi et al., 2019** | Crit Rev Food Sci Nutr | Meta Analysis Tabrizi Reza, Saneei Parvane, ... Asemi Zatollah. The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials. Cri...
**Barreto et al., 2023** | Eur J Sport Sci | Meta Analysis Barreto G, Loureiro L M R, ... Saunders B. Effects of caffeine chewing gum supplementation on exercise performance: A systematic review and meta-analysis. Eur J Sport Sci. 2023-May;23(5):714-...
**Low et al., 2024** | J Transl Med | Systematic Review Low Jazreel Ju-Li, Tan Brendan Jen-Wei, ... Tan Eng-King. Genetic susceptibility to caffeine intake and metabolism: a systematic review. J Transl Med. 2024-Oct-22;22(1):961. doi:10.1186/s12967-0...
**Liira et al., 2014** | Cochrane Database Syst Rev | Meta Analysis Liira Juha, Verbeek Jos H, ... Ruotsalainen Jani H. Pharmacological interventions for sleepiness and sleep disturbances caused by shift work. Cochrane Database Syst Rev. 2014-Aug-12;...
**Wang et al., 2022** | Nutrients | Meta Analysis Wang Ziyu, Qiu Bopeng, ... Del Coso Juan. Effects of Caffeine Intake on Endurance Running Performance and Time to Exhaustion: A Systematic Review and Meta-Analysis. Nutrients. 2022-Dec-28;15(1). doi:1...
**Asbaghi et al., 2024** | Br J Nutr | Meta Analysis Asbaghi Omid, Rezaei Kelishadi Mahnaz, ... Zamani Mohammad. The effects of green tea extract supplementation on body composition, obesity-related hormones and oxidative stress markers: a grade-asse...
**Phung et al., 2010** | Am J Clin Nutr | Systematic Review Phung Olivia J, Baker William L, ... Coleman Craig I. Effect of green tea catechins with or without caffeine on anthropometric measures: a systematic review and meta-analysis. Am J Clin Nutr...
**Guest et al., 2018** | Med Sci Sports Exerc | Rct Guest Nanci, Corey Paul, ... El-Sohemy Ahmed. Caffeine, CYP1A2 Genotype, and Endurance Performance in Athletes. Med Sci Sports Exerc. 2018-Aug;50(8):1570-1578. doi:10.1249/MSS.0000000000001596 PURPO...
The non-proteinic amino acid L-theanine and caffeine, a methylxanthine derivative, are naturally occurring ingredients in tea. The present study investigated the effect of a combination of 97 mg L-theanine and 40 mg caffeine as compared to placebo tr...
**Lorenzo et al., 2021** | Nutrients | Meta Analysis Lorenzo Calvo Jorge, Fei Xueyin, ... Pareja-Galeano Helios. Caffeine and Cognitive Functions in Sports: A Systematic Review and Meta-Analysis. Nutrients. 2021-Mar-06;13(3). doi:10.3390/nu13030868 C...
CONTEXT: The bioactive compounds found in tea from Camellia sinensis, namely theanine, caffeine, and polyphenols, can potentially improve short-term and long-term health outcomes. OBJECTIVE: The aim of this study was to assess the effects of tea, the...
**Abreu et al., 2023** | J Int Soc Sports Nutr | Systematic Review Abreu Rodrigo, Oliveira Catarina B, ... Teixeira Vitor H. Effects of dietary supplements on athletic performance in elite soccer players: a systematic review. J Int Soc Sports Nutr. 2...
**Fernández-Sánchez et al., 2024** | Nutrients | Meta Analysis Fernández-Sánchez Javier, Trujillo-Colmena Daniel, ... Collado-Mateo Daniel. Effect of Acute Caffeine Intake on Fat Oxidation Rate during Fed-State Exercise: A Systematic Review and Meta-...
The aim of this study was to compare 50 mg caffeine, with and without 100 mg L-theanine, on cognition and mood in healthy volunteers. The effects of these treatments on word recognition, rapid visual information processing, critical flicker fusion th...
BACKGROUND: Although the regular consumption of green tea or green tea extract has been considered to improve insulin sensitivity, the reported results are inconsistent. Therefore, we conducted a meta-analysis to evaluate the effect of green tea or g...
BACKGROUND AND AIMS: To examine the effect and safety of high-dose green tea extract (Epigallocatechin gallate, EGCG) at a daily dosage of 856.8 mg on weight reduction and changes of lipid profile and obesity-related hormone peptides in women with ce...
**Southward et al., 2018** | Sports Med | Meta Analysis Southward Kyle, Rutherfurd-Markwick Kay J, Ali Ajmol. The Effect of Acute Caffeine Ingestion on Endurance Performance: A Systematic Review and Meta-Analysis. Sports Med. 2018-Aug;48(8):1913-1928...
This study examined the effect of creatine nitrate and caffeine alone and combined on exercise performance and cognitive function in resistance-trained athletes. In a double-blind, randomized crossover trial, twelve resistance-trained male athletes w...
INTRODUCTION: Different outcomes of the effect of green tea on weight loss (WL) and weight maintenance (WM) have been reported in studies with subjects differing in ethnicity and habitual caffeine intake. PURPOSE: To elucidate by meta-analysis whethe...
**Baladia et al., 2014** | Nutr Hosp | Meta Analysis Baladia Eduard, Basulto Julio, ... Calbet David. [Effect of green tea or green tea extract consumption on body weight and body composition; systematic review and meta-analysis]. Nutr Hosp. 2014-Mar...
A systematic review and meta-analysis was conducted on 11 randomized placebo-controlled human studies of acute effects of tea constituents L-theanine and epigallocatechin gallate, administered alone or in combination with caffeine, on cognitive funct...
**Chen et al., 2020** | J Alzheimers Dis | Systematic Review Chen J Q Alida, Scheltens Philip, ... Ossenkoppele Rik. Associations Between Caffeine Consumption, Cognitive Decline, and Dementia: A Systematic Review. J Alzheimers Dis. 2020;78(4):1519-15...
**Collado-Mateo et al., 2020** | Nutrients | Meta Analysis Collado-Mateo Daniel, Lavín-Pérez Ana Myriam, ... Coso Juan Del. Effect of Acute Caffeine Intake on the Fat Oxidation Rate during Exercise: A Systematic Review and Meta-Analysis. Nutrients. 2...
**Al et al., 2025** | Nutrients | Systematic Review Al Shahab Shatha, Al Balushi Rawan, ... Jahrami Haitham. Efficiency of Different Supplements in Alleviating Symptoms of ADHD with or Without the Use of Stimulants: A Systematic Review. Nutrients. 20...
OBJECTIVE: Increased caffeine intake is associated with a lower risk of Parkinson disease (PD) and is neuroprotective in mouse models of PD. However, in a previous study, an exploratory analysis suggested that, in patients taking creatine, caffeine i...
**Dos et al., 2021** | Nutrition | Systematic Review Dos Santos Quaresma Marcus V L, Guazzelli Marques Camila, Nakamoto Fernanda Patti. Effects of diet interventions, dietary supplements, and performance-enhancing substances on the performance of Cro...
**Conger et al., 2023** | Int J Sport Nutr Exerc Metab | Meta Analysis Conger Scott A, Tuthill Lara M, Millard-Stafford Mindy L. Does Caffeine Increase Fat Metabolism? A Systematic Review and Meta-Analysis. Int J Sport Nutr Exerc Metab. 2023-Mar-01;3...
**Li et al., 2025** | Front Nutr | Systematic Review Li Yanfeng, Qiu Bopeng, ... Xu Kai. The acute effects of caffeine, creatine, and carbohydrate mouth rinse combined with conditioning activity on subsequent sports performance: a systematic review a...
**Randell et al., 2014** | Med Sci Sports Exerc | Rct Randell Rebecca K, Hodgson Adrian B, ... Jeukendrup Asker E. Variable duration of decaffeinated green tea extract ingestion on exercise metabolism. Med Sci Sports Exerc. 2014-Jun;46(6):1185-93. do...
**Montalvo-Alonso et al., 2024** | Nutrients | Rct Montalvo-Alonso Juan Jesús, Munilla César, ... Pérez-López Alberto. Acute Co-Ingestion of Caffeine and Sodium Bicarbonate on Muscular Endurance Performance. Nutrients. 2024-Dec-19;16(24). doi:10.3390...
**Cappelletti et al., 2015** | Curr Neuropharmacol | Meta Analysis Cappelletti Simone, Piacentino Daria, ... Aromatario Mariarosaria. Caffeine: cognitive and physical performance enhancer or psychoactive drug?. Curr Neuropharmacol. 2015-Jan;13(1):71-...
**Mancini et al., 2017** | Phytomedicine | Systematic Review Mancini Edele, Beglinger Christoph, ... Borgwardt Stefan. Green tea effects on cognition, mood and human brain function: A systematic review. Phytomedicine. 2017-Oct-15;34:26-37. doi:10.101...
**Wiese et al., 2023** | Int J Vitam Nutr Res | Systematic Review Wiese Fanny, Kutschan Sabine, ... Huebner Jutta. Green tea and green tea extract in oncological treatment: A systematic review. Int J Vitam Nutr Res. 2023-Feb;93(1):72-84. doi:10.1024/...
**Shekelle et al., 2003** | JAMA | Meta Analysis Shekelle Paul G, Hardy Mary L, ... Gagné James. Efficacy and safety of ephedra and ephedrine for weight loss and athletic performance: a meta-analysis. JAMA. 2003-Mar-26;289(12):1537-45 CONTEXT: Ephedr...
**Ishikawa et al., 2022** | Nutrients | Rct Ishikawa Akira, Matsuda Tomoka, ... Sakamaki-Sunaga Mikako. Effect of Green Tea Extract Ingestion on Fat Oxidation during Exercise in the Menstrual Cycle: A Pilot Study. Nutrients. 2022-Sep-21;14(19). doi:1...
L-theanine, an amino acid found in tea, and caffeine, found in tea and coffee, are claimed to enhance attention. We conducted a double-blind, placebo-controlled, counterbalanced, two-way crossover trial to determine the acute effects of a high-dose L...
**Brooks et al., 2016** | Nutr Rev | Systematic Review Brooks James R, Oketch-Rabah Hellen, ... Sarma Nandakumara D. Safety and performance benefits of arginine supplements for military personnel: a systematic review. Nutr Rev. 2016-Nov;74(11):708-72...
**Bobillo et al., 2018** | Eur J Nutr | Rct Bobillo Cecilia, Finlayson Graham, ... Mayer Marcos A. Short-term effects of a green coffee extract-, Garcinia c ambogia- and L-carnitine-containing chewing gum on snack intake and appetite regulation. Eur ...
**Hu et al., 2018** | Regul Toxicol Pharmacol | Systematic Review Hu Jiang, Webster Donna, ... Shao Andrew. The safety of green tea and green tea extract consumption in adults - Results of a systematic review. Regul Toxicol Pharmacol. 2018-Jun;95:412...
**Asbaghi et al., 2020** | Diabetes Metab Syndr | Meta Analysis Asbaghi Omid, Fouladvand Faezeh, ... Abbasnezhad Amir. Effect of green tea extract on lipid profile in patients with type 2 diabetes mellitus: A systematic review and meta-analysis. Diab...
**Ruiz-Moreno et al., 2021** | Eur J Nutr | Rct Ruiz-Moreno Carlos, Gutiérrez-Hellín Jorge, ... Del Coso Juan. Caffeine increases whole-body fat oxidation during 1 h of cycling at Fatmax. Eur J Nutr. 2021-Jun;60(4):2077-2085. doi:10.1007/s00394-020-0...
**Gutiérrez-Hellín et al., 2023** | Eur J Nutr | Rct Gutiérrez-Hellín Jorge, Aguilar-Navarro Millán, ... Del Coso Juan. Effect of caffeine intake on fat oxidation rate during exercise: is there a dose-response effect?. Eur J Nutr. 2023-Feb;62(1):311-...
**Luo et al., 2025** | J Int Soc Sports Nutr | Systematic Review Luo Hua, Tengku Kamalden Tengku Fadilah, ... Nasharuddin Nurul Amelina. Effects of different dietary supplements on athletic performance in soccer players: a systematic review and netwo...
This study investigated the effect of decaffeinated green tea extract (dGTE), with or without antioxidant nutrients, on fat oxidation, body composition and cardio-metabolic health measures in overweight individuals engaged in regular exercise. Twenty...
**Elosegui et al., 2022** | Int J Sport Nutr Exerc Metab | Systematic Review Elosegui Sara, López-Seoane Jaime, ... Pareja-Galeano Helios. Interaction Between Caffeine and Creatine When Used as Concurrent Ergogenic Supplements: A Systematic Review. I...
BACKGROUND: This study investigated the effects of combined Rhodiola rosea (RHO) and caffeine (CAF) supplementation on lower limb explosive power and fatigue recovery in volleyball players, aiming to validate their potential synergistic effects. METH...
PURPOSE: Previous studies have investigated the effect of single or combined caffeine (CAF) and L-theanine (THE) intake on attention performance. However, its effect on shooting performance and cognitive performance in a sport is unknown. The aim of ...
**Saavedra et al., 2024** | Nutr Hosp | Systematic Review Saavedra Velásquez Nicolas, Cuadrado Peñafiel Víctor, de la Vega Marcos Ricardo. Can caffeine improve your performance? Psychophysiological effects - A systematic review. Nutr Hosp. 2024-Jun-2...
**Ganio et al., 2009** | J Strength Cond Res | Systematic Review Ganio Matthew S, Klau Jennifer F, ... Maresh Carl M. Effect of caffeine on sport-specific endurance performance: a systematic review. J Strength Cond Res. 2009-Jan;23(1):315-24. doi:10....
Showing top 50 of 82 sources, sorted by quality score.
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Frequently Asked Questions
What is caffeine and what are its main benefits?
Caffeine is a widely studied stimulant used to enhance physical endurance, cognitive function, and metabolic processes. There is strong evidence for its use in improving athletic performance and moderate evidence for its benefits to cognitive function and weight management.
Does caffeine help with athletic performance?
Yes, there is strong evidence that caffeine enhances endurance running performance, increases time to exhaustion, and boosts fat oxidation rates during exercise. Research also indicates that caffeine chewing gum is an effective method for supplementing exercise performance.
Can caffeine improve focus and mental clarity?
There is moderate evidence that caffeine can improve cognitive performance, alertness, and mood. These benefits are particularly notable when caffeine is combined with L-theanine.
Can caffeine help with weight loss?
There is moderate evidence suggesting that caffeine may have potential effects on weight loss and body measurements. However, its specific impact on weight management is still being studied.
Is caffeine safe and are there any known interactions?
No drug interactions are documented, but your individual response to caffeine is heavily influenced by your genetics, specifically the CYP1A2 gene. This genetic variation significantly affects how you metabolize caffeine and how it impacts your athletic performance.
What is an effective dose of caffeine?
Studies have mentioned effective doses such as 50 mg of caffeine, which is often paired with 100 mg of L-theanine for cognitive benefits. Because your metabolism is influenced by your specific genotype, you should consider how your body personally responds to different amounts.
Answers generated from research evidence. Not medical advice.