Black tea (generic name)
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Interactions with Drugs
Studies of the interactions of black tea with drugs are limited. However, black tea is a source of caffeine, for which multiple interactions have been documented.
Black tea may increase the effects of drugs that cause the blood vessels to narrow (called vasopressors).
The combination of caffeine with ephedrine, an ephedra alkaloid, has been implicated in numerous severe or life-threatening cardiovascular events such as very high blood pressure, stroke, or heart attack. This combination is commonly used in over-the-counter weight loss products and may also be associated with other adverse effects, including abnormal heart rhythms, insomnia, anxiety, headache, irritability, poor concentration, blurred vision, and dizziness. Stroke has also been reported after the nasal ingestion of caffeine with amphetamine.
Caffeine may add to the effects and side effects of other stimulants including nicotine, beta-adrenergic agonists such as albuterol (Ventolin®), or other methylxanthines such as theophylline. Conversely, caffeine can counteract drowsy effects and mental slowness caused by benzodiazepines like lorazepam (Ativan®) or diazepam (Valium®). Phenylpropanolamine and caffeine should not be used together due to reports of numerous potentially serious adverse effects, although forms of phenylpropanolamine taken by mouth have been removed from the U.S. market due to reports of bleeding into the head.
When taken with caffeine, a number of drugs may increase caffeine blood levels or the length of time caffeine acts on the body, including disulfiram (Antabuse®), oral contraceptives (OCPs) or hormone replacement therapy (HRT), ciprofloxacin (Cipro®), norfloxacin, fluvoxamine (Luvox®), cimetidine (Tagamet®), verapamil, and mexiletine. Caffeine levels may be lowered by taking dexamethasone (Decadron®). The metabolism of caffeine by the liver may be affected by multiple drugs, although the effects in humans are not clear.
Caffeine may lengthen the effects of carbamazepine or increase the effects of clozapine (Clozaril®) and dipyridamole. Caffeine may affect serum lithium levels and abrupt cessation of caffeine use by regular caffeine users taking lithium may result in high levels of lithium or lithium toxicity. Levels of aspirin or phenobarbital may be lowered in the body, although clinical effects in humans are not clear.
Although caffeine by itself does not appear to have pain-relieving properties, it is used in combination with ergotamine tartrate in the treatment of migraine or cluster headaches (for example, Cafergot®). It has been shown to increase the headache relieving effects of other pain relievers such as acetaminophen and aspirin (for example, Excedrin®). Caffeine may also increase the pain relieving effects of codeine or ibuprofen (Advil®, Motrin®).
There is controversy as to how black tea and caffeine affect blood clotting. Black tea may contain vitamin K, which when used in large quantities can reduce the blood thinning effects of warfarin (Coumadin®), a phenomenon that has been reported in a human case. However, black tea may also increase the risk of bleeding when taken with anticoagulants or antiplatelet therapies. Caution is advised.
Based on preliminary data, theanine, a specific glutamate derivative in green tea (which is the same species as black tea), may reduce the adverse reactions caused to the heart and liver by the prescription cancer drug doxorubicin. Further research is needed to confirm these results.
Based on preliminary data, ingestion of green tea may lower LDL cholesterol and thus may theoretically interact with other cholesterol-lowering drugs.
Other potential interactions may include drugs such as adenosine, alcohol, antidiabetics, antipsychotics, fluconazole, hydrocortisone, levodopa, MAOI antidepressants, phenytoin, proton pump inhibitors (PPIs), riluzole, and timolol.
Interactions with Herbs and Dietary Supplements
Studies of black tea interactions with herbs and supplements are limited. However, black tea is a source of caffeine for which multiple interactions have been documented.
There is controversy as to how black tea and caffeine affect blood clotting. Caution is advised when using herbs or supplements that affect blood clotting.
Black tea may increase the effects of herbs or supplements that cause the blood vessels to narrow (called vasoconstrictors).
Black tea may increase or decrease the effects of antidiabetic agents.
Caffeine may add to the effects and side effects of other stimulants. The combination of caffeine with ephedrine, which is present in ephedra (ma huang), has been implicated in numerous severe or life-threatening cardiovascular events such as very high blood pressure, stroke, or heart attack. This combination is commonly used in over-the-counter weight loss products and may also be associated with other adverse effects including abnormal heart rhythms, insomnia, anxiety, headache, irritability, poor concentration, blurred vision, and dizziness.
Cola nut, guarana (Paullina cupana), and yerba mate (Ilex paraguariensis) are also sources of caffeine and may add to the effects and side effects of caffeine in black tea. A combination product containing caffeine, yerba mate (Ilex paraguariensis), and damiana (Turnera difussa) has been reported to cause weight loss, slowing of the gastrointestinal tract, and a feeling of stomach fullness.
As a diuretic, caffeine increases urine and sodium losses through the kidney and may add to the effects of other diuretic agents.
Based on preliminary data, ingestion of black tea may lower LDL cholesterol, and thus may theoretically interact with other cholesterol-lowering herbs and supplements.
Bitter orange, calcium, iron, MAOIs, and tannin-containing herbs and supplements may also interact.
Black tea may increase the effects of antioxidants.