Which method offers the most reliable way of assessing whether athletic performance is boosted by caffeine consumption?

Caffeine is a natural chemical with stimulant effects. It is found in coffee, tea, cola, cocoa, guarana, yerba mate, and over 60 other products.

Caffeine works by stimulating the central nervous system, heart, muscles, and the centers that control blood pressure. Caffeine can raise blood pressure, but might not have this effect in people who use it all the time. Caffeine can also act like a "water pill" that increases urine flow.

People most commonly use caffeine for mental alertness, headache, migraine, athletic performance, memory, and obesity. It is also used for asthma, gallbladder disease, ADHD, low blood pressure, depression, and many other conditions, but there is no good scientific evidence to support most of these other uses.

Caffeine products sold in very concentrated or pure forms are a health concern. People can easily take doses that are much too high by mistake. It's illegal in the US for these products to be sold to consumers in bulk. Taking caffeine, within limits, is allowed by the National Collegiate Athletic Association (NCAA). Urine concentrations over 15 mcg/mL are prohibited.

Side Effects

When taken by mouth: Caffeine is likely safe for most healthy adults when used in doses up to 400 mg daily. This is equal to about 4 cups of coffee.

Caffeine is possibly unsafe when used for a long time or in doses over 400 mg daily. Caffeine can cause insomnia, nervousness, restlessness, nausea, increased heart rate, and other side effects. Larger doses might cause headache, anxiety, and chest pain.

Caffeine is likely unsafe when used in very high doses. It can cause irregular heartbeat and even death. Products with very concentrated or pure caffeine have a high risk of being used in doses that are too high. Avoid using these products.

Special Precautions and Warnings

Pregnancy and breast-feeding: Caffeine is possibly safe during pregnancy and breast-feeding when used in amounts commonly found in foods. Consuming up to 300 mg of caffeine daily appears to be safe. This is about the amount in 3 cups of coffee. Consuming larger amounts during pregnancy or when breast-feeding is possibly unsafe. Caffeine might increase the chance of miscarriage and other problems. Caffeine can also pass into breast milk. High caffeine intake while nursing can cause sleeping problems, irritability, and increased bowel activity in breast-fed infants.

Children: Caffeine is possibly safe when used by children and adolescents in amounts commonly found in foods.

Anxiety disorders: Caffeine might make these conditions worse. Use caffeine cautiously and in low amounts if you have anxiety.

Bipolar disorder: Too much caffeine might make this condition worse. Use caffeine cautiously and in low amounts if you have bipolar disorder.

Bleeding disorders: Caffeine might aggravate bleeding disorders. Use caffeine cautiously if you have a bleeding disorder.

Heart conditions: Caffeine can cause irregular heartbeat in sensitive people. Use caffeine with caution.

Diabetes: Caffeine might affect the way the body uses sugar. If you have diabetes, use caffeine with caution.

Diarrhea: Caffeine, especially when taken in large amounts, might worsen diarrhea.

Epilepsy: People with epilepsy should avoid using caffeine in high doses. Low doses of caffeine should be used cautiously.

Glaucoma: Caffeine increases the pressure inside the eye. The increase occurs within 30 minutes and lasts for at least 90 minutes after drinking caffeinated beverages.

High blood pressure: Consuming caffeine might increase blood pressure in people with high blood pressure. But this does not seem to be a major concern in people who use caffeine regularly.

Loss of bladder control: Caffeine can make bladder control worse by increasing frequency of urination and the urge to urinate.

Irritable bowel syndrome (IBS): Caffeine, especially when taken in large amounts, might worsen diarrhea in people with IBS.

Weak bones (osteoporosis): Caffeine can increase the amount of calcium that is flushed out in the urine. If you have osteoporosis or low bone density, caffeine should be limited to less than 300 mg daily (approximately 2-3 cups of coffee).

Parkinson disease: Taking caffeine with creatine might make Parkinson disease worsen faster. If you have Parkinson disease and take creatine, use caffeine with caution.

Schizophrenia: Caffeine might worsen symptoms of schizophrenia.

Interactions ?

Major Interaction

Do not take this combination

• Stimulant drugs speed up the nervous system. Caffeine and ephedrine are both stimulant drugs. Taking caffeine along with ephedrine might cause too much stimulation and sometimes serious side effects and heart problems. Do not take caffeine-containing products and ephedrine at the same time.

Moderate Interaction

Be cautious with this combination

• Caffeine might block the effects of adenosine. Adenosine is often used by doctors to do a test on the heart called a cardiac stress test. Stop consuming caffeine-containing products at least 24 hours before a cardiac stress test.

• The body breaks down caffeine to get rid of it. Some antibiotics can decrease how quickly the body breaks down caffeine. Taking these drugs along with caffeine might increase the risk of side effects including jitteriness, headache, increased heart rate, and others.

• The body breaks down caffeine to get rid of it. Cimetidine can decrease how quickly your body breaks down caffeine. Taking cimetidine along with caffeine might increase the chance of caffeine side effects including jitteriness, headache, fast heartbeat, and others.

• The body breaks down clozapine to get rid of it. Caffeine seems to decrease how quickly the body breaks down clozapine. Taking caffeine along with clozapine can increase the effects and side effects of clozapine.

• Caffeine might block the effects of dipyridamole. Dipyridamole is often used by doctors to do a test on the heart called a cardiac stress test. Stop consuming caffeine-containing products at least 24 hours before a cardiac stress test.

• The body breaks down caffeine to get rid of it. Disulfiram can decrease how quickly the body gets rid of caffeine. Taking caffeine along with disulfiram might increase the effects and side effects of caffeine including jitteriness, hyperactivity, irritability, and others.

• The body breaks down caffeine to get rid of it. Estrogens can decrease how quickly the body breaks down caffeine. Taking caffeine along with estrogens might increase the side effects of caffeine, including jitteriness, headache, and fast heartbeat.

• The body breaks down caffeine to get rid of it. Fluvoxamine can decrease how quickly the body breaks down caffeine. Taking caffeine along with fluvoxamine might increase the effects and side effects of caffeine.

• Caffeine can increase how quickly your body gets rid of lithium. If you take products that contain caffeine and you take lithium, don't stop taking caffeine products all at once. Instead, reduce use slowly. Stopping caffeine too quickly can increase the side effects of lithium.

• There is some concern that caffeine can interact with certain medications, called MAOIs. If caffeine is taken with these medications, it might increase the risk for serious side effects including fast heartbeat and very high blood pressure.

  Some common MAOIs include phenelzine (Nardil), selegiline (Zelapar), and tranylcypromine (Parnate).

• Caffeine might slow blood clotting. Taking caffeine along with medications that also slow blood clotting might increase the risk of bruising and bleeding.

• The stimulant effects of caffeine can block the sleep-producing effects of pentobarbital.

• Caffeine can stimulate the body. Phenylpropanolamine can also stimulate the body. Taking caffeine along with phenylpropanolamine might cause too much stimulation and increase heartbeat, blood pressure, and cause nervousness.

• Taking caffeine along with riluzole might decrease how fast the body breaks down riluzole. This might increase the effects and side effects of riluzole.

• Stimulants, such as amphetamines and cocaine, speed up the nervous system. By speeding up the nervous system, stimulant medications can increase blood pressure and speed up the heartbeat. Caffeine can also speed up the nervous system. Taking caffeine along with stimulant drugs might cause serious problems including increased heart rate and high blood pressure.

• Caffeine works similarly to theophylline. Caffeine can also decrease how quickly the body gets rid of theophylline. Taking theophylline along with caffeine might increase the effects and side effects of theophylline.

• Verapamil can decrease how quickly the body gets rid of caffeine. Taking caffeine along with verapamil can increase the risk of caffeine side effects including jitteriness, headache, and an increased heartbeat.

• Caffeine can stimulate the heart. Some medications for asthma can also stimulate the heart. Taking caffeine with some medications for asthma might cause too much stimulation and cause heart problems.

• Caffeine might lower the effects of carbamazepine. Taking caffeine with carbamazepine can reduce its effects and increase the risk of seizures in some people.

• Ethosuximide is used to control certain types of seizures. Caffeine might lower the effects of ethosuximide. Taking caffeine with ethosuximide might reduce its effects and increase the risk of seizures.

• Felbamate is used to control certain types of seizures. Caffeine might lower the effects of felbamate. Taking caffeine with felbamate might reduce its effects and increase the risk of seizures.

• The body breaks down flutamide to get rid of it. Caffeine might decrease how quickly the body breaks down flutamide. Taking caffeine along with flutamide might increase the effects and side effects of flutamide.

• Phenobarbital is used to control some types of seizures. Caffeine might lower the effects of phenobarbital and increase the risk of seizures in some patients.

• Phenytoin is used to control some types of seizures. Caffeine might lower the effects of phenytoin. Taking caffeine with phenytoin might reduce its effects and increase the risk of seizures.

• Valproate is used to control some types of seizures. Caffeine might lower the effects of valproate and increase the risk of seizures in some patients.

• Caffeine can decrease potassium levels. "Water pills" can also decrease potassium levels. Taking caffeine along with "water pills" might make potassium levels drop too low.

• Taking caffeine along with nicotine might increase the risk for rapid heart rate and high blood pressure.

• Caffeine might increase the amount of pioglitazone that the body absorbs. Taking caffeine might increase the effects and adverse effects of pioglitazone.

Minor Interaction

Be watchful with this combination

• The body breaks down caffeine to get rid of it. Alcohol can decrease how quickly the body breaks down caffeine. Taking caffeine along with alcohol might increase the effects and side effects of caffeine, including jitteriness, headache, and fast heartbeat.

• The body breaks down caffeine to get rid of it. Birth control pills can decrease how quickly the body breaks down caffeine. Taking caffeine along with birth control pills can cause jitteriness, headache, fast heartbeat, and other side effects.

• The body breaks down caffeine to get rid of it. Fluconazole might decrease how quickly the body gets rid of caffeine. Taking caffeine along with fluconazole might cause caffeine to stay in the body too long and increase the risk of side effects such as nervousness, anxiety, and insomnia.

• Caffeine can either increase or decrease blood sugar. Diabetes medications are used to lower blood sugar. Taking some medications for diabetes along with caffeine might change the effects of the diabetes medications. Monitor your blood sugar closely. The dose of your diabetes medication might need to be changed.

• Mexiletine can decrease how quickly the body breaks down caffeine. Taking Mexiletine along with caffeine might increase the effects and side effects of caffeine.

• Terbinafine can decrease how fast the body gets rid of caffeine. Taking caffeine along with terbinafine can increase the risk of caffeine side effects including jitteriness, headache, and increased heartbeat.

• Caffeine is changed and broken down by the liver. Some drugs decrease how quickly the liver changes and breaks down caffeine. This could change the effects and side effects of [topic].

• Metformin can decrease how quickly the body breaks down caffeine. Taking metformin along with caffeine might increase the effects and side effects of caffeine.

• Methoxsalen can decrease how quickly the body breaks down caffeine. Taking methoxsalen along with caffeine might increase the effects and side effects of caffeine.

• Phenothiazines can decrease how quickly the body breaks down caffeine. Taking phenothiazines along with caffeine might increase the effects and side effects of caffeine.

• Tiagabine is used to control some types of seizures. Caffeine does not seem to influence the effects of tiagabine. But long-term caffeine use might increase blood levels of tiagbine.

• Ticlopidine can decrease how fast the body gets rid of caffeine. Taking caffeine along with ticlopidine can increase the risk of caffeine side effects.

Dosing

Caffeine is found in many foods and beverages, including coffee, teas, chocolate, and many sports and energy drinks. Coffee contains 95-200 mg of caffeine per cup. Black tea contains 25-110 mg of caffeine per cup. Green tea contains 30-50 mg of caffeine per cup. Caffeine products sold in very concentrated or pure forms are a health concern. People can easily take doses that are much too high by mistake. Avoid these products.

As medicine, caffeine has most often been used by adults in doses of 50-260 mg by mouth daily. Speak with a healthcare provider to find out what type of product and dose might be best for a specific condition.

CONDITIONS OF USE AND IMPORTANT INFORMATION: This information is meant to supplement, not replace advice from your doctor or healthcare provider and is not meant to cover all possible uses, precautions, interactions or adverse effects. This information may not fit your specific health circumstances. Never delay or disregard seeking professional medical advice from your doctor or other qualified health care provider because of something you have read on WebMD. You should always speak with your doctor or health care professional before you start, stop, or change any prescribed part of your health care plan or treatment and to determine what course of therapy is right for you.

This copyrighted material is provided by Natural Medicines Comprehensive Database Consumer Version. Information from this source is evidence-based and objective, and without commercial influence. For professional medical information on natural medicines, see Natural Medicines Comprehensive Database Professional Version. © Therapeutic Research Faculty 2018.

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