Related Terms

• 1,3,7-Trimethylxanthine, 1,3-dimethylxanthine, 1,7-dimethylxanthine, 3,7-dimethylxanthine, 7-methyltheophylline, acetaminophen-caffeine, adenosine antagonist, anhydrous caffeine, aspirin-acetaminophen-caffeine, aspirin-salicylamide-caffeine, black tea, bronchodilator, butalbital-aspirin-caffeine, C8H10N4O2, cacao beans, cafeína (Spanish), caffea, caffedrine, caffeina citrata, caffeina citrata effervescens, caffeine anhydrous, caffeine choline, caffeine citrate, caffeine citrated intravenous, caffeine citrated oral, caffeine-sodium benzoate, chocolate, citrated caffeine, cocoa, Coffea, coffee, coffee beans, diuretic, effervescent citrated caffeine, energy drink, ergogenic aid, ergotamine-caffeine, espresso, green tea, guarana, guarana berries, kola nut, methylxanthine, orphenadrine-aspirin-caffeine, paraxanthine, psychoactive drug, soft drinks, stimulant, tea, theobromine, theophylline, trimethylxanthine, xanthine, yerba mate.

• Select products and brand names: Cafcit®, Enerjets®, NoDoz®, NoDoz® Maximum Strength, Stay Awake®, Vivarin®.

• Select combination products: Actamin® Super (acetaminophen and caffeine); Anacin®, Anacin® Advanced Headache Formula, Excedrin®, Goody's® Extra Strength, Goody's® Cool Orange, Vanquish® (acetaminophen, aspirin, and caffeine); Bayer® Headache Relief (aspirin and caffeine); Cafergot®, Cafetrate®, Cafertrine®, Ercaf®, Ergo-Caff®, Gotamine®, Migergot®, Wigraine® (ergotamine and caffeine); Fiorinal® (aspirin, butalbital, and caffeine); Fiorinal® with Codeine No. 3 (aspirin, butalbital, caffeine, and codeine), Medi-First® Pain Relief, Medi-First® Pain Zapper (aspirin, acetaminophen, salicylamide, caffeine); Midol® Complete (acetaminophen, pyrilamine maleate, and caffeine); Norgesic®, Norgesic® forte (orphenadrine citrate, aspirin, caffeine); Revive® energy mints (caffeine, guarana, ginseng, green tea, açaí berry, mangosteen, and goji berry).

• Note: Caffeine is found in many foods and drinks, including black tea, green tea, and yerba mate. Separate summaries are available on these topics. Products containing caffeine are not addressed in detail in this summary.

Background

• Caffeine is a naturally occurring compound found in the leaves, seeds, or fruits of more than 60 plants, including coffee (Coffea arabica) beans, cacao (Theobroma cacao) beans, kola (Cola acuminata) nuts, guarana (Paullinia cupana) berries, and tea (Camellia sinensis) leaves. Caffeine is consumed regularly in the United States and throughout the world. It is found in many beverages, including coffee, chocolate, some energy drinks, and tea. More than seven kilograms of caffeine per person are consumed in the United States per year.

• Caffeine was first discovered in 1819 by the German chemist Friedlieb Ferdinand Runge. He coined the term Kaffein, a chemical compound in coffee, which became caffeine in English.

• Humans have consumed caffeine since the Stone Age. It was during this time that people discovered that chewing the seeds, bark, and leaves of certain plants reduced fatigue, increased awareness, and improved mood. The first known pot of tea dates back to 2737 BC, when the Chinese emperor Shen Nung boiled drinking water when the leaves of a nearby bush fell into the pot. Coffee was first noted in Africa around AD 575, when beans were used as money and eaten as food. Arabians of the 11th Century were known to have coffee beverages. In 1519, Spanish conquerors were treated to a chocolate drink by the Aztec emperor Montezuma. The world's first caffeinated soft drinks were created in the 1880s.

• In people, caffeine may be useful to stimulate the heart and increase urine flow. Caffeine has been shown to affect mood, endurance, the brain, and blood vessels, as well as activity in both the stomach and colon. Caffeine has also been marketed as a weight loss tool and is often included in various weight loss supplements.

Scientific Evidence

Tradition/Theory

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious and should be evaluated by a qualified health care professional.

• Aging, alcohol abuse, allergies, amyotrophic lateral sclerosis (ALS), anti-inflammatory, antioxidant, bladder disorders, bowel health, brain tumors, cancer, cataracts, cavities, cerebral insufficiency (decreased blood flow to the brain), cocaine dependence, diuretic (increases urine flow), eczema (inflamed and irritated skin), epilepsy (seizure), gallstones, gout, Huntington's disease, immune system regulation, insecticide, ischemic heart disease (decreased blood flow to the heart), kidney disorders, low blood pressure (upon standing), malaria, motion sickness, multiple sclerosis, nausea and vomiting during pregnancy, neurological disorders (Joubert syndrome), photoprotection (protection from UV radiation), sepsis (bacterial infection of the blood or tissues), schizophrenia, sinusitis (nasal sinus inflammation), snoring, traumatic brain injury, UV-induced erythema prevention/sunburn, vasorelaxant (relaxes blood vessel walls), viral infections, vitiligo (white patches on the skin), work shift sleep disorder.

Dosing

The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.

Adults (18 years and older)

• For alertness, 200 milligrams of caffeine has been taken by mouth for different durations.

• For cocaine dependence, 300-1,200 milligrams of caffeine has been taken by mouth three times daily (with or without biperiden) for 10 days.

• For cognitive performance, 50-600 milligrams of caffeine has been taken by mouth daily for various durations. In sleep-deprived people, 800 milligrams of caffeinated chewing gum has been taken by mouth throughout the night for four days (in 200-milligram doses every two hours).

• For type 2 diabetes, about 400 milligrams daily has been taken. In type 1 diabetes, 200 milligrams of caffeine has been taken by mouth daily for three months.

• For exercise performance, 1-9 milligrams of caffeine per kilogram of body weight or 200-300 milligrams of caffeine has been taken by mouth prior to exercise.

• For headache, a cup of caffeinated coffee or a combination of caffeine and pain relievers (such as aspirin or acetaminophen) have been taken. A single 300-milligram dose of caffeine has also been taken by mouth after childbirth, in women with postdural puncture headache. 300-500 milligrams of caffeine has been injected into the veins once or twice daily. Single or repeated doses of 0.5 grams of caffeine sodium benzoate have been injected into the veins or muscles.

• For intermittent claudication (muscle pain in the limbs), six milligrams of caffeine per kilogram of body weight has been taken by mouth prior to physical performance testing.

• For liver disease, about two cups of coffee have been taken by mouth daily.

• For mood, a caffeinated cup of coffee containing around 75 milligrams of caffeine has been taken by mouth prior to mood testing.

• For obsessive compulsive disorder (OCD), 300 milligrams of caffeine in addition to either a serotonin reuptake inhibitor (SSRI) or serotonin norepinephrine reuptake inhibitor (SNRI) agent has been taken by mouth daily for five weeks.

• For pain, 5-10 milligrams of caffeine per kilogram of body weight has been taken by mouth one hour prior to moderate-to-high-intensity exercise testing.

• For Parkinson's disease, a 300-milligram increase in caffeine intake has been taken.

• For respiratory disorders, 5-9 milligrams of caffeine per kilogram of body weight has been taken by mouth.

• For weight loss, about 50-200 milligrams of caffeine is contained in each pill of common, commercially available weight loss supplements.

Children (under 18 years old)

• For apnea (interrupted breathing) in infants, an initial loading dose of 5-10 milligrams of caffeine per kilogram of body weight has been taken. After 24 hours, a maintenance dose of 2.5-5 milligrams of caffeine per kilogram of body weight has been taken daily. Doses have been given either by mouth or injected directly into the veins or muscles. For apnea associated with viral lung infection, a single dose of five milligrams of caffeine per kilogram of body weight has been injected, followed by a similar second dose if needed.

• For attention-deficit hyperactivity disorder (ADHD), 80-500 milligrams of caffeine has been taken by mouth daily, as either a single or divided dose, for an unknown duration.

• For kwashiorkor (a form of childhood malnutrition), a beverage containing 40 milligrams of caffeine (equal to 3.8-5.6 milligrams of caffeine per kilogram of body weight) has been taken via a nasal stomach tube.

Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

• Avoid with known allergy or hypersensitivity to caffeine. A temporary rise in heart rate and blood pressure has been reported in those who are hypersensitive to caffeine. Urticaria (skin rash and hives) after consuming coffee has also been reported. Historically, inhalation of coffee bean dust may produce "coffee worker's lung," a type of allergic lung inflammation.

Side Effects and Warnings

• Individuals who metabolize caffeine differently may be at increased risk for side effects.

• Stomach irritation or upset, nausea, diarrhea, abdominal pain, and loss of bowel control may occur with caffeine intake. Caffeine may increase levels of stress hormones (including cortisol, epinephrine, and norepinephrine) and stimulate ulcer formation. Coffee may increase stomach acid production and increase the incidence of acid reflux heartburn, gastroesophageal reflux disease (GERD), regurgitation, and difficult or painful swallowing. Coffee may also speed up the process of stomach emptying, possibly leading to injury of the intestinal tissue.

• Other possible side effects of caffeine include agitation, airway inflammation, anxiety, daytime sleepiness, dehydration, delayed conception, depleted carbon monoxide levels in the blood, depression, difficulty thinking clearly, display of anger, drowsiness, fatigue, headaches, hyperactivity, impaired alertness and attention, impaired memory retention, increased chronic back pain, increased frequency and severity of premenstrual syndrome (PMS), increased occurrence of gallstone polyps, increased risk of Parkinson's disease and multiple sclerosis, increased risky behavior (including binge drinking, drinking and driving, sexual activity, and suicidal acts), irritability, jitteriness, lack of energy, loss of B vitamins, mild delirium, nervousness, overactive reflexes, panic attacks, poor feeding, reduced blood potassium levels, reduced semen quality, restlessness, shortened menstrual cycle, sleep disturbances, suppressed immune function, sweating, teeth grinding, wakefulness, and worsened liver damage,

• Caffeine is a known stimulant agent and may increase heart rate or cause irregular heartbeats. Caffeine may also be associated with adverse effects on blood vessel function and increased risk of ischemic stroke (blocked blood flow to the brain). Use cautiously in people with a known history of abnormal heart rhythms.

• Caffeine is a known diuretic (an agent that increases urine production). Use cautiously in people with an overactive bladder or other urologic disorders and in those taking other diuretic agents. Caffeine may increase voiding, give a sense of urgency, and irritate the bladder.

• Although it has not been well studied in humans, caffeine may increase the risk of bleeding. Caution is advised in people with bleeding disorders and in those taking drugs that may increase the risk of bleeding (including warfarin). Dosing adjustments may be necessary.

• Caffeine may increase blood sugar levels. Caution is advised in people with diabetes or hypoglycemia and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.

• Caffeine may increase blood pressure. Caution is advised in people with high blood pressure and in those taking drugs, herbs, or supplements that lower blood pressure (including phenylpropanolamine).

• Caffeine may increase blood lipids. Caution is advised in people with elevated blood lipids and in those taking drugs, herbs, or supplements that alter lipid levels.

• Caffeine may be associated with seizures. Caution is advised in people with seizure disorders and those taking any drugs to prevent or treat seizures, or when combined with any agents that lower the seizure threshold (including carbamazepine, phenobarbital, phenytoin, valproate, and ethosuximide).

• Use cautiously in people with heightened sensitivity to caffeine.

• Use cautiously in people with movement disorders or those using drugs that may cause such disorders (e.g., neuroleptics). Caffeine may cause muscle tremors, impair muscle coordination, or provoke disorders that cause uncontrolled movement (e.g., familial paroxysmal nonkinesigenic dyskinesia).

• Use cautiously in people with osteoporosis or those at risk for osteoporosis, as caffeine may decrease bone mineral density, promote bone loss, and increase fracture risk.

• Use cautiously in people with sleep disorders like insomnia and in those taking other central nervous system (CNS) stimulants, as caffeine may increase these effects and cause insomnia.

• Use cautiously in people with glaucoma, as caffeine may increase eye pressure.

• Use cautiously in people at risk for kidney stones, as caffeine has been associated with higher urinary calcium, therefore posing an increased risk.

• Use cautiously in people with eating disorders, as a high incidence of caffeine consumption may increase the risk of anxiety and mood disorders.

• Use cautiously in people who have a weakened immune system and in those using immune system-lowering agents, as caffeine may alter immune function, particularly after exercise.

• Use cautiously in people with breast disease, stomach disorders, growth hormone deficiency, or high-grade inflammation; those at risk for kidney or breast cancer; and those who do not consume caffeine regularly (including athletes), due to and increased risk for side effects.

• Use cautiously in firefighters wearing protective clothing, as they may be more susceptible to heat-related fatigue and injury.

• Use cautiously over prolonged periods of time. Chronic caffeine use may result in increased tolerance and dependence.

• Use cautiously in combination with adenosine, agents that affect dopamine, agents that affect the liver's cytochrome P enzyme system (e.g., amitriptyline, ciprofloxacin, clozapine, coconut products, danshen (Salvia miltiorrhiza), disulfiram, echinacea (Echinacea spp.), enoxacin, ethinyl estradiol, flutamide, fluvoxamine, furafylline, genistein, grapefruit juice, imipramine, kudzu (Pueraria lobata), melatonin, methoxsalen, methylxanthines, mexiletine, omeprazole, phenothiazines, and riluzole), agents that depress the central nervous system (e.g., diazepam, midazolam, triazolam, zolpidem, and zopiclone), agents that dilate or constrict blood vessels, agents that mimic the effects of the sympathetic nervous system, antidepressants (e.g., monoamine oxidase inhibitors; MAOIs), antipyrine, calcium, corticosteroids, creatine, fluconazole, geranium (Geranium spp.), iron, lithium, magnesium, and potassium.

• Use cautiously in children and the elderly.

• Use cautiously for periods greater than four weeks in preterm infants, due to the risk of reduced weight gain and increased oxygen consumption.

• Caffeine may pass through breast milk. Use cautiously in amounts greater than three cups of coffee daily in breastfeeding women.

• Avoid amounts greater than 200 milligrams daily in pregnant women.

• Avoid in people with rosacea (enlarged facial blood vessels).

• Avoid in people with Marfan syndrome (a connective tissue disorder), as agents like caffeine that stimulate the cardiovascular system should not be used with this disorder.

• Avoid in people with autosomal recessive polycystic kidney disease (a type of genetic kidney disease), as caffeine may promote kidney cyst growth.

• Avoid use before adenosine, cardiac, or dipyridamole stress testing, due to potential interference with results.

• Avoid use in combination with agents that stimulate the central nervous system, alcohol, and herbs that contain caffeine.

• Avoid in those with known allergy or hypersensitivity to caffeine. Elevated heart rate, increased blood pressure, urticaria (skin rash and hives), and allergic lung inflammation have been reported following caffeine and coffee exposure.

Pregnancy and Breastfeeding

• Although it has not been well studied in humans, the consumption of one cup of coffee daily may be associated with a lowered chance of getting pregnant.

• Possible side effects of caffeine use during pregnancy include increased risk of early delivery, miscarriage, neural tube defects (especially spinal cord malformations such as spina bifida), and stillbirth. Possible side effects on the baby include impaired skeletal growth, decreased length, and reduced birthweight,

• Use cautiously during pregnancy, as caffeine may pass through the placenta and reach the baby. Also, the clearance of caffeine from the body may be extended during this time. Avoid use of more than 200 milligrams daily in pregnant women.

• Use cautiously in breastfeeding women, as caffeine may pass through breast milk and reach the baby. This is particularly important for premature babies, as their ability to break down caffeine may not be fully developed yet. Avoid more than three cups of coffee daily in breastfeeding women.

• In babies, possible side effects of caffeine use during breastfeeding include irritability, jitteriness, restlessness, stimulatory effects, wakefulness, poor feeding, and mild iron deficiency due to decreased iron in breast milk.

Interactions

Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy.

Interactions with Drugs

• Caffeine may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants (blood thinners) such as warfarin (Coumadin®) or heparin, antiplatelet drugs such as clopidogrel (Plavix®), and nonsteroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).

• Caffeine may raise blood sugar levels. Caution is advised when using medications that may affect blood sugar (such as metformin). Patients taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.

• Caffeine may increase blood pressure. Caution is advised in patients taking drugs, herbs, or supplements that may affect blood pressure.

• Caffeine may interfere with the way the body processes certain drugs using the liver's cytochrome P450 enzyme system (e.g., ticlopidine). As a result, the levels of these drugs may be altered in the blood and may change the intended effects. Patients taking any medication should check the package insert and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.

• Caffeine may also interact with adenosine, agents that affect dopamine, agents that increase urine production, agents that mimic sympathetic nervous system activity (e.g., phenylpropanolamine (PPA)), agents that narrow and widen blood vessels (e.g., nifedipine), agents that regulate heart rate, agents that widen airways, alcohol, Alzheimer's agents, amphetamine, antiandrogens (e.g., flutamide), antiasthma drugs (e.g., furafylline), antibiotics, anticancer drugs (e.g., cisplatin, cyclophosphamide, doxorubicin, ifosfamide, mitomycin C, pazopanib, and temozolomide), antidepressants, antifungals (e.g., terfenadine), antiglaucoma agents, antiobesity agents (e.g., ephedrine), antiparkinsonians (e.g., levodopa), antipsychotics (e.g., phenothiazines), antipyrine, antiseizure drugs (e.g., carbamazepine, ethosuximide, felbamate, phenobarbital, phenytoin, terfenadine, and valproic acid), antiulcer agents (e.g., cimetidine), barbiturates (e.g., pentobarbital), benzodiazepines (e.g., lorazepam), beta-agonists, beta-blockers (e.g., propranolol), calcium salts, celecoxib, central nervous system (CNS) depressants (e.g., diazepam, midazolam, triazolam, zolpidem, zopiclone), clozapine, CNS stimulants, cocaine, contraceptives, corticosteroids, darifenacin, decongestants, dipyridamole, disulfiram, drugs that may lower the seizure threshold, ergot derivatives, estrogens, flubendiamide, fluconazole, fluvoxamine, growth hormone, H2 blockers, hydrocortisone, immune system-lowering agents, inotropes, iron salts, lipid-lowering drugs, lithium, magnesium supplements, methoxsalen, methylenedioxymethamphetamine (MDMA, or "Ecstasy"), methylphenidate, methylxanthines, mexiletine, morphine, nicotine, oseltamivir (Tamiflu®), pain relievers (e.g., acetaminophen, aspirin, ibuprofen, and tramadol), perazine, potassium salts, potassium-depleting drugs, proton pump inhibitors (PPIs) (e.g., omeprazole), quinolones (e.g., ciprofloxacin), riluzole, rosuvastatin, sedatives, terbinafine, and theophylline.

Interactions with Herbs and Dietary Supplements

• Caffeine may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.

• Caffeine may raise blood sugar levels. Caution is advised when using herbs or supplements that may also affect blood sugar. Blood glucose levels may require monitoring, and doses may need adjustment.

• Caffeine may increase blood pressure. Caution is advised in patients taking drugs, herbs, or supplements that may affect blood pressure.

• Caffeine may interfere with the way the body processes certain herbs or supplements using the liver's cytochrome P450 enzyme system. As a result, the levels of other herbs or supplements may be altered in the blood. It may also alter the effects that other herbs or supplements possibly have on the P450 system.

• Tyramine- or tryptophan-containing foods may cause dangerously high blood pressure when taken at the same time as agents that have properties similar to monoamine oxidase inhibitor drugs (MAOIs). These include protein foods that have been aged or preserved. Specific examples of foods are anchovies, avocados, bananas, bean curd, beer (alcohol-free or reduced), caffeine (large amounts), caviar, champagne, cheeses (particularly aged, processed, or strong varieties), chocolate, dry sausage or salami or bologna, fava beans, figs, herring (pickled), liver (particularly chicken), meat tenderizers, papaya, protein extracts or powder, raisins, shrimp paste, sour cream, soy sauce, wine (particularly chianti), yeast extracts, and yogurt.

• Caffeine may also interact with Alzheimer's agents; antiasthma agents; antibacterials; anticancer herbs and supplements; antidepressants; antiglaucoma agents; antiobesity herbs and supplements (e.g.; ephedra (ma huang)); antioxidants; antiseizure herbs and supplements; antiulcer herbs and supplements; athletic performance enhancers; B vitamins; bitter orange; caffeine-containing herbs, supplements, foods, and drinks; calcium; calcium-containing foods and drinks; capsicum; coconut products; cola nut; contraceptives; cordyceps; creatine; damiana; danshen; echinacea; genistein; geranium; grapefruit juice; guarana; herbs and supplements that increase urine production; herbs and supplements that lower lipids; herbs and supplements that may lower the seizure threshold; herbs and supplements that mimic sympathetic nervous system activity; herbs and supplements that narrow and widen blood vessels; herbs and supplements that widen airways; high-carbohydrate meals; immune system-lowering herbs and supplements; inotropes; iron-containing foods; iron salts; isoflavone-containing foods; kudzu; Liu Wei Di Huang Wan; magnesium; melatonin; pain relievers; phytoestrogens; potassium; potassium-containing foods; potassium-depleting herbs and supplements; red pepper; sedatives; stimulants; sulfo-carrabiose; tea (black and green); theanine; vitamin B-containing foods; vitamin C; vitamin C-containing foods; vitamin K; vitamin K-containing foods; yerba mate; zinc; and zinc-containing foods.

Author Information

• This information is based on a systematic review of scientific literature edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

References

Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.

1. Dellermalm J, Segerdahl M, Grass S. Caffeine does not attenuate experimentally induced ischemic pain in healthy subjects. Acta Anaesthesiol Scand 2009;53(10):1288-1292. View Abstract

2. Goldstein ER, Ziegenfuss T, Kalman D, et al. International society of sports nutrition position stand: caffeine and performance. J Int Soc Sports Nutr 2010;7(1):5. View Abstract

3. Henderson-Smart DJ, Steer PA. Caffeine versus theophylline for apnea in preterm infants. Cochrane Database Syst Rev 2010;(1):CD000273. View Abstract

4. Ker K, Edwards PJ, Felix LM, et al. Caffeine for the prevention of injuries and errors in shift workers. Cochrane Database Syst Rev 2010;(5):CD008508. View Abstract

5. MacKenzie T, Comi R, Sluss P, et al. A. Metabolic and hormonal effects of caffeine: randomized, double-blind, placebo-controlled crossover trial. Metabolism 2007;56(12):1694-1698. View Abstract

6. Momsen AH, Jensen MB, Norager CB, et al. Randomized double-blind placebo-controlled crossover study of caffeine in patients with intermittent claudication. Br J Surg 2010;97(10):1503-1510. View Abstract

7. Noordzij M, Uiterwaal CS, Arends LR, et al. Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials. J Hypertens 2005;23(5):921-928. View Abstract

8. Olson CA, Thornton JA, Adam GE, et al. Effects of 2 adenosine antagonists, quercetin and caffeine, on vigilance and mood. J Clin Psychopharmacol 2010;30(5):573-578. View Abstract

9. Pfaffenrath V, Diener HC, Pageler L, et al. OTC analgesics in headache treatment: open-label phase vs randomized double-blind phase of a large clinical trial. Headache 2009;49(5):638-645. View Abstract

10. Simmonds MJ, Minahan CL, Sabapathy S. Caffeine improves supramaximal cycling but not the rate of anaerobic energy release. Eur J Appl Physiol 2010;109(2):287-295. View Abstract

11. Skinner TL, Jenkins DG, Coombes JS, et al. Dose response of caffeine on 2000-m rowing performance. Med Sci Sports Exerc 2010;42(3):571-576. View Abstract

12. Smillie LD, Gokcen E. Caffeine enhances working memory for extraverts. Biol Psychol 2010;85(3):496-498. View Abstract

13. Turk MW, Yang K, Hravnak M, et al. Randomized clinical trials of weight loss maintenance: a review. J Cardiovasc Nurs 2009;24(1):58-80. View Abstract

14. VanHaitsma TA, Mickleborough T, Stage JM, et al. Comparative effects of caffeine and albuterol on the bronchoconstrictor response to exercise in asthmatic athletes. Int J Sports Med 2010;31(4):231-236. View Abstract

15. Welsh EJ, Bara A, Barley E, et al. Caffeine for asthma. Cochrane Database Syst Rev 2010;(1):CD001112. View Abstract