Antiulcer medication. Coffee increases stomach acidity and reduces the effectiveness of nor-
mal doses of cimetidine and other antiulcer medication.
False-positive test for pheochromocytoma. Pheochromocytoma, a tumor of the adrenal glands,
secretes adrenalin, which is converted to VMA (vanillylmandelic acid) by the body and
excreted in the urine. Until recently, the test for this tumor measured the levels of VMA in
the patient’s urine and coffee, which contains VMA, was eliminated from patients’ diets lest
it elevate the level of VMA in the urine, producing a false-positive test result. Today, more
finely drawn tests make this unnecessary.
Iron supplements. Caffeine binds with iron to form insoluble compounds your body cannot
absorb. Ideally, iron supplements and coffee should be taken at least two hours apart.
Birth control pills. Using oral contraceptives appears to double the time it takes to eliminate
caffeine from the body. Instead of five to six hours, the stimulation of one cup of coffee may
last as long as 12 hours.
Monoamine oxidase (MAO) inhibitors. Monoamine oxidase inhibitors are drugs used to treat
depression. They inactivate naturally occurring enzymes in your body that metabolize tyra-
mine, a substance found in many fermented or aged foods. Tyramine constricts blood vessels
and increases blood pressure. Caffeine is a substance similar to tyramine. If you consume
excessive amounts of a caffeinated beverage such as coffee while you are taking an MAO
inhibitor, the result may be a hypertensive crisis.
Nonprescription drugs containing caffeine. The caffeine in coffee may add to the stimulant
effects of the caffeine in over-the-counter cold remedies, diuretics, pain relievers, stimulants,
and weight-control products containing caffeine. Some cold pills contain 30 mg caffeine,
some pain relievers 130 mg, and some weight-control products as much as 280 mg caffeine.
There are 110–150 mg caffeine in a five-ounce cup of drip-brewed coffee.
Sedatives. The caffeine in coffee may counteract the drowsiness caused by sedative drugs;
this may be a boon to people who get sleepy when they take antihistamines. Coffee will
not, however, “sober up” people who are experiencing the inebriating effects of alcoholic
beverages.
Theophylline. Caffeine relaxes the smooth muscle of the bronchi and may intensify the
effects (and/or increase the risk of side effects) of this antiasthmatic drug.
Coffee