As already mentioned, some potentially harmful effects of coffee are recognized, particularly for people who should take few or no stimulants. Beyond this however, scientific studies of the effects of caffeine have in general failed to prove negative effects, although some have produced contradictory conclusions. An individual study may produce interesting results which may suggest fruitful directions for further research, but usually it is only when several independent studies confirm one another, and any contradictory results can be accounted for, that one can have reasonable confidence in the safety of a drug — particularly an “” optional”” one like coffee.
Although caffeine does not fall into the class of “”addictive”” drugs, it may be habit-forming. Some people may experience headache, fatigue, irritability and nervousness when their daily intake of caffeine is quickly and substantially altered.
Such “”withdrawal effects”” may be responsible for confusing results in some studies. There are many complicating factors in long-term studies. One is the familiar “”convergence of risk-factors”” (e.g. that coffee-drinkers may be more likely to be smokers). Another is that many of the study subjects may deliberately change (or have previously changed) their consumption habits or behaviour, e.g. in response to discovering that they suffer from hypertension. There may also be significant differences in methods of coffee preparation between study populations, or over long periods of time.
North Las Vegas, Nevada, USA