Scientific articles

Black tea

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What is it?
Black tea is a product made from the Camellia sinesis plant. The aged leaves and stems are used to make medicine. Green tea, which is made from fresh leaves of the same plant, has some different properties.

Black tea is used for improving mental alertness as well as learning, memory and information processing skills. It is also used for treating headache and low blood pressure; preventing heart disease, including “hardening of the arteries” (atherosclerosis) and heart attack; preventing Parkinson's disease; and reducing the risk of stomach and colon cancer, lung cancer, ovarian cancer, and breast cancer. It is also used for type 2 diabetes, stomach disorders, vomiting, diarrhea, and as a diuretic to increase urine flow. Some people use black tea for preventing tooth decay and kidney stones. In combination with various other products, black tea is used for weight loss.

In foods, black tea is consumed as a hot or cold beverage.

How effective is it?

Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.

The effectiveness ratings for BLACK TEA are as follows:
Likely effective for...

    Mental alertness. Drinking black tea and other caffeinated beverages throughout the day helps to keep people alert, even after extended periods without sleep.

Possibly effective for...

    Hardening of the arteries (atherosclerosis). Early research shows that people who drink black tea seem to have a reduced risk of having their arteries become hardened. This link is stronger in women than men.
    Low blood pressure after eating (postprandial hypotension). Drinking beverages containing caffeine, such as black tea, helps increase blood pressure in older people who have low blood pressure after eating.
    Kidney stones. Women who drink black tea seem to have an 8% lower risk of developing kidney stones.
    Heart attacks. Some research shows that people who drink black tea have a lower risk of having a heart attack. Also, people who have been drinking black tea for at least a year before having a heart attack seem to be less likely to die after having a heart attack.
    Brittle bones (osteoporosis). Early research shows that older women who drink more black tea seem to have stronger bones. Drinking more black tea also seems to be linked with a lower risk of hip fracture in older men and women.
    Ovarian cancer. Women who regularly drink tea, including black tea or green tea, appear to have a lower risk of developing ovarian cancer compared to women who never or rarely drink tea.
    Parkinson's disease. Some research shows that people who drink caffeinated beverages such as coffee, tea, and cola have a lower risk of Parkinson's disease. The lower risk seems to be directly related to the dose of caffeine in men but not women. Drinking black tea also appears to be linked with a reduced risk of Parkinson's disease among people who smoke cigarettes.

Possibly ineffective for...

    Breast cancer. People who drink black tea do not seem to have a lower risk of breast cancer.
    Colon and rectal cancer. Some early research suggests that drinking black or green tea might be linked with a lower risk of colon and rectal cancer. However, most research shows that drinking tea is not linked with a lower risk of colon and rectal cancer. In fact, some early research suggests that drinking higher amounts of black tea might be linked with an increased risk of colon and rectal cancer.
    Diabetes. Early research suggests that taking an extract of black and green tea does not improve HbA1C levels in people with diabetes. HbA1C is a measure of blood sugar control. Other early research suggests that drinking at least one cup of black tea per day is not linked with a lower risk of developing type 2 diabetes in Japanese adults.
    Stomach cancer. Some early research suggests that drinking black or green tea might be linked with a lower risk of stomach cancer. However, most research shows that people who drink black or green tea do not have a lower risk. In fact, some early research suggests that drinking higher amounts of black tea might be linked with an increased risk of stomach cancer.
    High cholesterol. Some research shows that black tea might reduce total cholesterol and low-density lipoprotein (LDL or “bad”) cholesterol in people with normal or high cholesterol levels. However, most research shows that drinking black tea does not have these effects.
    High blood pressure. Some early research suggests that people who regularly drink green or black tea have a lower risk of having high systolic blood pressure, which is the top number of a blood pressure reading. However, most research shows that drinking black tea does not reduce blood pressure in people with normal or high blood pressure.

Insufficient evidence to rate effectiveness for...

    Bladder cancer. Some early research suggests that people who drink black or green tea might have a lower risk of urinary tract cancers. However, other research shows that drinking black tea is not linked with a reduced risk of bladder cancer.
    Heart disease. Some early research suggests that people who regularly drink black tea have a lower risk of developing heart disease. However, other research suggests that drinking black tea is linked with an increased risk of heart disease becoming worse or causing death.
    Cavities. Early research suggests that rinsing with a black tea extract might prevent cavities.
    Kidney cancer. Early research suggests that people who drink more black or green tea have a higher risk of developing kidney cancer.
    Lung cancer. Green tea and black tea contain chemicals called phytoestrogens. Some research shows that men who get more phytoestrogens in their diet have a lower risk of developing lung cancer than men who do not get these chemicals. However other early research suggests that drinking black tea is not linked with a reduced risk of lung cancer and may even be linked with an increased risk.
    Mouth cancer. Early research shows that black tea might help prevent mouth cancer in patients with lesions in the mouth that may turn into cancer.
    Pancreatic cancer. Some early research suggests that drinking black tea is linked with a reduced risk of pancreatic cancer risk. However, other research shows conflicting results.
    Prostate cancer. Early evidence suggests that drinking black tea is linked with a reduced risk of prostate cancer.
    Stress. Early research suggests that drinking black tea for 6 weeks does not improve blood pressure, heart rate, or feelings of stress ratings while performing stressful tasks.
    Stroke. Black tea contains chemicals called flavonoids. Early research suggests that eating a diet that contains flavonoids is linked with a lower risk of stroke.
    Weight loss. Early research suggests that taking a combination product containing black tea extract plus green tea extract, asparagus, guarana, kidney bean, and mate along with a combination of kidney bean pods, garcinia, and chromium yeast for 12 weeks does not reduce body weight in overweight adults.
    Stomach disorders.
    Vomiting.
    Diarrhea.
    Headache.
    Other conditions.

More evidence is needed to rate the effectiveness of black tea for these uses.

How does it work?
Black tea contains 2% to 4% caffeine, which affects thinking and alertness, increases urine output, and may reduce the symptoms of Parkinson's disease. It also contains antioxidants and other substances that might help protect the heart and blood vessels.

Are there safety concerns?
Drinking moderate amounts of black tea is LIKELY SAFE for most adults.

Drinking too much black tea, such as more than five cups per day, is POSSIBLY UNSAFE. High amounts of black tea can cause side effects due to the caffeine in black tea. These side effects can range from mild to serious and include headache, nervousness, sleep problems, vomiting, diarrhea, irritability, irregular heartbeat, tremor, heartburn, dizziness, ringing in the ears, convulsions, and confusion. Also, people who drink black tea or other caffeinated beverages all the time, especially in large amounts, can develop psychological dependence.

Drinking very high amounts of black tea containing more than 10 grams of caffeine is LIKELY UNSAFE. Doses of black tea this high might cause death or other severe side effects.

Caffeine is PROBABLY SAFE in children in amounts commonly found in foods.

Special precautions & warnings:
Children: Black tea is POSSIBLY SAFE when taken by mouth by children in amounts commonly found in foods.

Pregnancy and breast-feeding: If you are pregnant or breast-feeding, drinking black tea in small amounts is POSSIBLY SAFE. Do not drink more than 3 cups a day of black tea. This amount of tea provides about 200 mg of caffeine. Consuming more than this amount during pregnancy is POSSIBLY UNSAFE and has been linked to an increased risk of miscarriage, increased risk of sudden infant death syndrome (SIDS), and other negative effects, including symptoms of caffeine withdrawal in newborns and lower birth weight.

If you are breast-feeding, drinking more than 3 cups a day of black tea is POSSIBLY UNSAFE and might cause your baby to become more irritable and have more bowel movements.

Anemia: Drinking black tea may make anemia worse in people with iron deficiency.

Anxiety disorders: The caffeine in black tea might make these conditions worse.

Bleeding disorders: There is some reason to believe that the caffeine in black tea might slow blood clotting, though this hasn’t been shown in people. Use caffeine cautiously if you have a bleeding disorder.

Heart problems: Caffeine in black tea can cause irregular heartbeat in certain people. If you have a heart condition, use caffeine with caution.

Diabetes: The caffeine in black tea might affect blood sugar. Use black tea with caution if you have diabetes.

Diarrhea: Black tea contains caffeine. The caffeine in black tea, especially when taken in large amounts, can worsen diarrhea.

Seizures: Black tea contains caffeine. There is a concern that high doses of caffeine might cause seizures or decrease the effects of drugs used to prevent seizures. If you have ever had a seizure, don’t use high doses of caffeine or caffeine-containing supplements such as black tea.

Glaucoma: Drinking caffeinated black tea increases the pressure inside the eye. The increase occurs within 30 minutes and lasts for at least 90 minutes.

Hormone-sensitive condition such as breast cancer, uterine cancer, ovarian cancer, endometriosis, or uterine fibroids: Black tea might act like estrogen. If you have any condition that might be made worse by exposure to estrogen, don’t use black tea.

High blood pressure: The caffeine in black tea might increase blood pressure in people with high blood pressure. However, this doesn't seem to occur in people who drink black tea or other caffeinated products regularly.

Irritable bowel syndrome (IBS): Black tea contains caffeine. The caffeine in black tea, especially when taken in large amounts, can worsen diarrhea and might worsen symptoms of IBS.

Brittle bones (osteoporosis): Drinking caffeinated black tea can increase the amount of calcium that is flushed out in the urine. This might weaken bones. Don’t drink more than 300 mg of caffeine per day (approximately 2-3 cups of black tea). Taking extra calcium may help to make up for calcium losses. Older women who have a genetic condition that affects the way they use vitamin D, should use caffeine with caution.

Overactive bladder: The caffeine in black tea might increase the risk of developing an overactive bladder. Also, black tea might increase symptoms in people who already have an overactive bladder. Black tea should be used with caution in these people.

Are there interactions with medications?

Moderate
    Be cautious with this combination.
Adenosine (Adenocard)
    Black tea contains caffeine. The caffeine in black tea might block the effects of adenosine (Adenocard). Adenosine (Adenocard) is often used by doctors to do a test on the heart. This test is called a cardiac stress test. Stop drinking black tea or other caffeine-containing products at least 24 hours before a cardiac stress test.
Antibiotics (Quinolone antibiotics)
    The body breaks down caffeine to get rid of it. Some antibiotics might decrease how quickly the body breaks down caffeine. Taking these antibiotics along with black tea can increase the risk of side effects including jitteriness, headache, increased heart rate, and other side effects.

    Some antibiotics that decrease how quickly the body breaks down caffeine include ciprofloxacin (Cipro), enoxacin (Penetrex), norfloxacin (Chibroxin, Noroxin), sparfloxacin (Zagam), trovafloxacin (Trovan), and grepafloxacin (Raxar).
Benzodiazepines
    Benzodiazepines are drugs that have calming effects. Black tea contains caffeine. Caffeine is a stimulant. Taking black tea along with benzodiazepines might block the calming effects of can benzodiazepines. Some benzodiazepines include alprazolam (Xanax), clonazepam (Klonopin), diazepam (Valium), lorazepam (Ativan), and others.
Carbamazepine (Tegretol)
    Carbamazepine is a drug used to treat seizures. Caffeine in black tea can decrease the effects of carbamazepine. Taking black tea with carbamazepine might decrease the effects of carbamazepine and increase the risk of seizures in some people.
Cimetidine (Tagamet)
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Cimetidine (Tagamet) can decrease how quickly your body breaks down caffeine. Taking cimetidine (Tagamet) along with black tea might increase the chance of caffeine side effects including jitteriness, headache, fast heartbeat, and others.
Clozapine (Clozaril)
    The body breaks down clozapine (Clozaril) to get rid of it. The caffeine in black tea seems to decrease how quickly the body breaks down clozapine (Clozaril). Taking black tea along with clozapine (Clozaril) can increase the effects and side effects of clozapine (Clozaril).
Dipyridamole (Persantine)
    Black tea contains caffeine. The caffeine in black tea might block the affects of dipyridamole (Persantine). Dipyridamole (Persantine) is often used by doctors to do a test on the heart. This test is called a cardiac stress test. Stop drinking black tea or other caffeine-containing products at least 24 hours before a cardiac stress test.
Disulfiram (Antabuse)
    The body breaks down caffeine to get rid of it. Disulfiram (Antabuse) can decrease how quickly the body gets rid of caffeine. Taking black tea (which contains caffeine) along with disulfiram (Antabuse) might increase the effects and side effects of caffeine including jitteriness, hyperactivity, irritability, and others.
Ephedrine
    Stimulant drugs speed up the nervous system. Black tea contains caffeine. Caffeine and ephedrine are both stimulant drugs. Taking black tea 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.
Estrogens
    The body breaks down the caffeine in black tea to get rid of it. Estrogens can decrease how quickly the body breaks down caffeine. Taking estrogen pills and drinking black tea can cause jitteriness, headache, fast heartbeat, and other side effects. If you take estrogen pills, limit your caffeine intake.

    Some estrogen pills include conjugated equine estrogens (Premarin), ethinyl estradiol, estradiol, and others.
Ethosuximide
    Ethosuximide is a drug used to treat seizures. Caffeine in black tea can decrease the effects of ethosuximide. Taking black tea with ethosuximide might decrease the effects of ethosuximide and increase the risk of seizures in some people.
Felbamate
    Felbamate is a drug used to treat seizures. Caffeine in black tea can decrease the effects of felbamate. Taking black tea with felbamate might decrease the effects of felbamate and increase the risk of seizures in some people.
Flutamide (Eulexin)
    The body breaks down flutamide (Eulexin) to get rid of it. Caffeine in black tea might decrease how quickly the body gets rid of flutamide. This could cause flutamide to stay in the body too long and increase the risk of side effects.
Fluvoxamine (Luvox)
    The body breaks down the caffeine in black tea to get rid of it. Fluvoxamine (Luvox) can decrease how quickly the body breaks down caffeine. Taking caffeine along with fluvoxamine (Luvox) might cause too much caffeine in the body, and increase the effects and side effects of caffeine.
Lithium
    Your body naturally gets rid of lithium. The caffeine in black tea can increase how quickly your body gets rid of lithium. If you take products that contain caffeine and you take lithium, stop taking caffeine products slowly. Stopping caffeine too quickly can increase the side effects of lithium.
Medications for asthma (Beta-adrenergic agonists)
    Black tea contains caffeine. 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.

    Some medications for asthma include albuterol (Proventil, Ventolin, Volmax), metaproterenol (Alupent), terbutaline (Bricanyl, Brethine), and isoproterenol (Isuprel).
Medications for depression (MAOIs)
    The caffeine in black tea can stimulate the body. Some medications used for depression can also stimulate the body. Drinking black tea and taking some medications for depression might cause too much stimulation of the body and serious side effects including fast heartbeat, high blood pressure, nervousness, and others.

    Some of these medications used for depression include phenelzine (Nardil), tranylcypromine (Parnate), and others.
Medications that change the liver (Cytochrome P450 1A2 (CYP1A2) inhibitors)
    Black tea contains caffeine. Caffeine is broken down by the liver. Some medications decrease how well the liver breaks down other medications. These medications that change the liver might decrease how fast caffeine in black tea is broken down in the body. This might increase the effects and side effects of caffeine in black tea. Some medications that change the liver include cimetidine (Tagamet), ciprofloxacin (Cipro), fluvoxamine (Luvox), and others.
Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)
    Black tea contains caffeine. Caffeine might slow blood clotting. Taking black tea along with medications that also slow clotting might increase the chances of bruising and bleeding.

    Some medications that slow blood clotting include aspirin, clopidogrel (Plavix), diclofenac (Voltaren, Cataflam, others), ibuprofen (Advil, Motrin, others), naproxen (Anaprox, Naprosyn, others), dalteparin (Fragmin), enoxaparin (Lovenox), heparin, warfarin (Coumadin), and others.
Nicotine
    Black tea contains caffeine. Caffeine can stimulate the heart. Nicotine can also stimulate the heart. Taking caffeine with nicotine might cause too much stimulation and cause heart problems, such as increased heart rate or blood pressure.
Pentobarbital (Nembutal)
    The stimulant effects of the caffeine in black tea can block the sleep-producing effects of pentobarbital.
Phenobarbital
    Phenobarbital is a drug used to treat seizures. Caffeine in black tea can decrease the effects of phenobarbital. Taking black tea with phenobarbital might decrease the effects of phenobarbital and increase the risk of seizures in some people.
Phenylpropanolamine
    The caffeine in black tea can stimulate the body. Phenylpropanolamine can also stimulate the body. Taking caffeine and phenylpropanolamine together might cause too much stimulation and increase heartbeat, blood pressure, and cause nervousness.
Phenytoin
    Phenytoin is a drug used to treat seizures. Caffeine in black tea can decrease the effects of phenytoin. Taking black tea with phenytoin might decrease the effects of phenytoin and increase the risk of seizures in some people.
Riluzole (Rilutek)
    The body breaks down riluzole (Rilutek) to get rid of it. Drinking black tea can decrease how quickly the body breaks down riluzole (Rilutek) and increase the effects and side effects of riluzole.
Stimulant drugs
    Stimulant drugs speed up the nervous system. By speeding up the nervous system, stimulant medications can make you feel jittery and speed up your heartbeat. The caffeine in black tea can also speed up the nervous system. Drinking black tea along with stimulant drugs might cause serious problems including increased heart rate and high blood pressure. Avoid taking stimulant drugs along with black tea.

    Some stimulant drugs include diethylpropion (Tenuate), epinephrine, phentermine (Ionamin), pseudoephedrine (Sudafed), and many others.
Theophylline
    Black tea contains caffeine. Caffeine works similarly to theophylline. Caffeine can also decrease how quickly the body gets rid of theophylline. This might cause increased effects and side effects of theophylline.
Valproate
    Valproate is a drug used to treat seizures. Caffeine in black tea can decrease the effects of valproate. Taking black tea with valproate might decrease the effects of valproate and increase the risk of seizures in some people.
Verapamil (Calan, Covera, Isoptin, Verelan)
    The body breaks down the caffeine in black tea to get rid of it. Verapamil (Calan, Covera, Isoptin, Verelan) can decrease how quickly the body gets rid of caffeine. Drinking black tea and taking verapamil (Calan, Covera, Isoptin, Verelan) can increase the risk of side effects for caffeine including jitteriness, headache, and an increased heartbeat.
Warfarin (Coumadin)
    Warfarin (Coumadin) is used to slow blood clotting. Large amounts of black tea might decrease how well warfarin (Coumadin) slows blood clotting. Decreasing how well warfarin (Coumadin) slows blood clotting might increase the risk of clotting. It is unclear why this interaction might occur. Be sure to have your blood checked regularly. The dose of your warfarin (Coumadin) might need to be changed.
Water pills (Diuretic drugs)
    Black tea contains caffeine. Caffeine, especially in excessive amounts, can reduce potassium in the body. "Water pills" can also decrease potassium in the body. Taking caffeine-containing products along with "water pills" might decrease potassium in the body too much.

    Some "water pills" that can decrease potassium include chlorothiazide (Diuril), chlorthalidone (Thalitone), furosemide (Lasix), hydrochlorothiazide (HCTZ, HydroDIURIL, Microzide), and others.
Minor
    Be watchful with this combination.
Alcohol
    Black tea contains caffeine. The body breaks down the caffeine in black tea to get rid of it. Alcohol can decrease how quickly the body breaks down caffeine. Taking black tea along with alcohol might cause too much caffeine in the bloodstream and caffeine side effects including jitteriness, headache, and fast heartbeat.
Birth control pills (Contraceptive drugs)
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Birth control pills can decrease how quickly the body breaks down caffeine. Taking black tea along with birth control pills might cause jitteriness, headache, fast heartbeat, and other side effects.

    Some birth control pills include ethinyl estradiol and levonorgestrel (Triphasil), ethinyl estradiol and norethindrone (Ortho-Novum 1/35, Ortho-Novum 7/7/7), and others.
Fluconazole (Diflucan)
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Fluconazole (Diflucan) might decrease how quickly the body gets rid of caffeine. This could cause caffeine to stay in the body too long and increase the risk of side effects such as nervousness, anxiety, and insomnia.
Medications for depression (Tricyclic antidepressants)
    Black tea contains chemicals called tannins. Tannins can bind to many medications and decrease how much medicine the body absorbs. To avoid this interaction, avoid black tea 1 hour before and 2 hours after taking medications for depression called tricyclic antidepressants.

    Some medications for depression include amitriptyline (Elavil) or imipramine (Tofranil, Janimine).
Medications for diabetes (Antidiabetes drugs)
    Black tea contains caffeine. Caffeine might increase blood sugar. Diabetes medications are used to lower blood sugar. By increasing blood sugar, black tea might decrease the effectiveness of diabetes medications. Monitor your blood sugar closely. The dose of your diabetes medication might need to be changed.

    Some medications used for diabetes include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, pioglitazone (Actos), rosiglitazone (Avandia), chlorpropamide (Diabinese), glipizide (Glucotrol), tolbutamide (Orinase), and others.
METFORMIN (Glucophage)
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Metformin (Glucophage) can decrease how quickly the body breaks down caffeine. Taking black tea along with metformin might cause too much caffeine in the body, and increase the effects and side effects of caffeine.
Methoxsalen (Oxsoralen)
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Methoxsalen (Oxsoralen) can decrease how quickly the body breaks down caffeine. Taking caffeine along with methoxsalen might cause too much caffeine in the body, and increase the effects and side effects of caffeine.
Mexiletine (Mexitil)
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Mexiletine (Mexitil) can decrease how quickly the body breaks down caffeine. Taking Mexiletine (Mexitil) along with black tea might increase the caffeine effects and side effects of black tea.
Phenothiazines
    Black tea contains chemicals called tannins. Tannins can bind to many medications and decrease how much medicine the body absorbs. To avoid this interaction, avoid black tea one hour before and two hours after taking phenothiazine medications.

    Some phenothiazine medications include fluphenazine (Permitil, Prolixin), chlorpromazine (Thorazine), haloperidol (Haldol), prochlorperazine (Compazine), thioridazine (Mellaril), and trifluoperazine (Stelazine).
Terbinafine (Lamisil)
    The body breaks down the caffeine in black tea to get rid of it. Terbinafine (Lamisil) can decrease how quickly the body gets rid of caffeine and increase the risk of side effects including jitteriness, headache, increased heartbeat, and other effects.
Tiagabine
    Black tea contains caffeine. Taking caffeine over a long time period along with tiagabine can increase the amount of tiagabine in the body. This might increase the side effects of tiagabine.
Ticlopidine (Ticlid)
    The body breaks down the caffeine in black tea to get rid of it. Ticlopidine (Ticlid) can decrease how quickly the body gets rid of caffeine. Taking black tea along with ticlopidine might increase the effects and side effects of caffeine, including jitteriness, hyperactivity, irritability, and others.

Are there interactions with herbs and supplements?

Bitter orange
    Using bitter orange along with other products that contain caffeine, such as black tea, can increase blood pressure and heart rate in otherwise healthy adults with normal blood pressure. This could increase the risk of serious heart problems.
Caffeine-containing herbs and supplements
    Black tea contains caffeine. Using it along with other herbs and supplements that contain caffeine might increase the risk of caffeine side effects. Natural products that contain caffeine include coffee, black tea, green tea, oolong tea, guarana, mate, and others.
Calcium
    High caffeine intake from foods and beverages, including black tea, flushes calcium out of the body in the urine.
Cordyceps
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Cordyceps might increase how quickly the body gets rid of caffeine. This might decrease the effects of caffeine.
Creatine
    There is some concern that combining caffeine, an ingredient in black tea, with ephedra and creatine might increase the risk of serious harmful effects. There is a report of stroke in an athlete who consumed 6 grams of creatine monohydrate, 400-600 mg of caffeine, 40-60 mg of ephedra, and a variety of other supplements daily for 6 weeks. Caffeine might also decrease whatever benefit creatine might have on athletic performance.
Danshen
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Danshen can decrease how quickly the body gets rid of caffeine. Drinking black tea and taking danshen might increase the risk of side effects for caffeine, including jitteriness, headache, and an increased heartbeat.
Echinacea
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Echinacea can decrease how quickly the body gets rid of caffeine. Drinking black tea and taking echinacea might increase the risk of side effects for caffeine, including jitteriness, headache, and an increased heartbeat.
Ephedra (Ma huang)
    Ephedra and black tea are both stimulants. They speed up the central nervous system. Using them together might speed it up too much, increasing the risk of high blood pressure, heart attack, stroke, seizures, and death. Don't take black tea with ephedra or other stimulants.
Folic acid
    Black tea might reduce the amount of folate that the body can absorb and use.
Herbs and supplements that might slow blood clotting
    Black tea might slow blood clotting. Using it along with other herbs and supplements that might also slow blood clotting could increase the risk of bruising and bleeding in some people. Some of these herbs include angelica, clove, danshen, garlic, ginger, ginkgo, Panax ginseng, and others.
Iron
    Black tea might interfere with the body's ability to absorb iron. This probably isn't a problem for most people, unless they are iron-deficient. If this is the case, drink tea between meals rather than with meals to lessen this interaction.
Kudzu
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Kudzu can decrease how quickly the body gets rid of caffeine. Drinking black tea and taking kudzu might increase the risk of side effects for caffeine, including jitteriness, headache, and an increased heartbeat.
Magnesium
    Drinking large amounts of black tea can increase the amount of magnesium that is flushed out in the urine.
Melatonin
    Black tea contains caffeine. Taking caffeine and melatonin together can increase melatonin levels. Caffeine can also increase natural melatonin levels in healthy individuals.
Red clover
    Black tea contains caffeine. The body breaks down caffeine to get rid of it. Chemicals in red clover can decrease how quickly the body gets rid of caffeine. Drinking black tea and taking red clover might increase the risk of side effects for caffeine, including jitteriness, headache, and an increased heartbeat.

Are there interactions with foods?

Iron
    Black tea might interfere with the body's ability to absorb iron. This probably isn't a problem for most people, unless they are iron-deficient. If this is the case, drink tea between meals rather than with meals to lessen this interaction.
Milk
    Adding milk to black tea appears to reduce some of the heart health benefits of drinking tea. Milk might bind with the antioxidants in tea and keep them from being absorbed. However, not all research confirms this. More evidence is needed to determine just how important this interaction, if any, might be.

What dose is used?
An 8-ounce serving of black tea provides from 40-120 mg of caffeine, the active ingredient.