The New Complete Book of Food
monoamine oxidase inhibitors, phenylpropanolamine, and theophylline. In addition, suddenly
decreasing your caffeine intake may increase blood levels of lithium, a drug used to control
mood swings. If you are taking one of these medicines, check with your doctor regarding your
consumption of caffeinated beverages.
Allopurinol. Tea and other beverages containing the methylxanthine stimulants (caffeine,
theophylline, and theobromine) reduce the effectiveness of the xanthine inhibitor, antigout
drug allopurinol.
Antibiotics. Drinking tea increases stomach acidity, which reduces the absorption of the
antibiotics ampicillin, erythromycin, griseofulvin, penicillin, and tetracycline.
Anticoagulants. Green tea is high in vitamin K, the blood-clotting vitamin produced natu-
rally by bacteria in our intestines. Using foods rich in vitamin K while you are taking an
anticoagulant (warfarin, Coumadin, Panwarfin) may reduce the effectiveness of the antico-
agulant, so larger doses are required.
Antiulcer medication. Drinking tea makes the stomach more acid and may reduce the effec-
tiveness of normal doses of cimetidine and other antiulcer medication.
Iron supplements. Caffeine and tannic acid bind with iron to form insoluble compounds
your body cannot absorb. Ideally, iron supplements and tea should be taken at least two
hours apart.
Monoamine oxidase (MAO) inhibitors. Monoamine oxidase inhibitors are drugs used to
treat depression. They inactivate naturally occurring enzymes in your body that metabolize
tyramine, a substance found in many fermented or aged foods. Tyramine constricts blood
vessels and increases blood pressure. Caffeine has some similarity to tyramine; if you con-
sume excessive amounts of a caffeinated beverage such as tea while you are taking an MAO
inhibitor, the result may be a hypertensive crisis.
Nonprescription drugs containing caffeine. The caffeine in brewed tea may add to the stimu-
lant effects of the caffeine in some cold remedies, diuretics, pain relievers, stimulants, and
weight-control products. Some over-the-counter cold pills contain 30 mg caffeine, some pain
relievers 130 mg, and some weight-control products as much as 280 mg caffeine. There are
21 to 47 mg caffeine in a five-ounce cup of brewed tea.
Sedatives. The caffeine in tea may counteract the drowsiness caused by sedative drugs.
Theophylline. The theophylline and caffeine in brewed tea may intensify the effects and/or
increase the risk of side effects from this antiasthmatic drug.