76 Caffeine
early twentieth century one standard medical textbook warned of coffee ad-
diction peril, and another medical volume described coffee as a gateway to
opiate addiction. In a modern study volunteers showed no particular desire
for caffeine but did find that 300 mg mimicked some effects ofdextroam-
phetamine. Although caffeine is not a scheduled substance, users can develop
a physical dependence on the drug that results in withdrawal symptoms in-
cluding weariness and headache. Such symptoms are not inevitable nor are
they necessarily troubling to persons experiencing them. In 2000 an interna-
tional panel of experts convened by European drug regulation agencies de-
scribed caffeine’s potential for dependence as low. Tolerance can develop to
some of caffeine’s effects.
Drug interactions.Caffeine itself can reduce headache, and an experiment
involving hundreds of participants showed caffeine to substantially improve
ibuprofen’s ability to relieve headache. Phenylpropanolamine is a drug com-
monly found in remedies for colds. It seems to increase caffeine levels in a
person using both drugs, and together the two can produce mood elevation,
hyperactivity and manic behavior, confusion, high blood pressure, and stroke.
In rat experiments, caffeine boosts the effects ofcocaineand amphetamine,
enough to transform normally tolerable doses into fatal ones. Human obser-
vations show that cocaine users tend to take lower doses of that drug if they
also use caffeine. Perhaps the most common drug taken with caffeine isnic-
otine. Animal experiments find that interactions of that combination may
make cigarette smoking more pleasurable. Cigarette smoking increases the
body’s rate of metabolizing caffeine, which decreases the influence from a
given amount of caffeine; British researchers found that smokers tend to use
more caffeine than nonsmokers. Birth control pills can double the time that a
given amount of caffeine lasts in the body. The drug can reduce drowsiness
produced bypentobarbital, and it can reducediazepam’s interference with
cognitive function. Caffeine is a traditional remedy for alcohol intoxication,
but in fact it does not speed alcohol’s elimination from the body, although
caffeine’s stimulant properties may help a drunken person function better.
Estrogen replacement therapy appears to interfere with women’s ability to
metabolize caffeine.
Cancer.Caffeine does not seem to produce cancer in animal experiments.
Indeed, green and black tea reduce development of cancer in mice, an effect
in which caffeine is believed to play a part. In humans, however, caffeine is
suspected of promoting premenopausal ovarian cancer and also cancer of the
pancreas and bladder.
Pregnancy.Experiments examining caffeine’s influence on pregnancy yield
conflicting results, which may indicate the question is particularly complex or
may simply mean that caffeine is an “invalid variable” having no effect. Here
are examples. A 1994 survey of 259 women in the Netherlands found that
caffeine raised the likelihood of becoming pregnant, but when the same subject
was examined in the 1980s among almost 2,000 women in Connecticut, caf-
feine was found to suppress fertility. During the 1990s a study of farm couples
in Canada found that caffeine had no effect on fertility but that coffee-drinking
women and tea-drinking men had lower birthrates, suggesting involvement
of something besides caffeine in the natural products’ effect. Rat experimen-