There is very probably little difference in the way coffee works on men or women. Rather, dominant factors would be body size and weight, and also genetic predisposition.
Update January 2009: A 2008 study in Barcelona of 688 university students claims that coffee affects men more than women. However, this is based on subjective self-administered tests after drinking espresso coffee and the differences are not great. In some cases the difference is not greater than the margin of error for the experiment. You can see the results at the journal Progress in Neuro-Psychopharmacology and Biological Psychiatry Vol 32, Issue 7, p. 1698.
Dose or efficacy (the way a drug works) for any drug is based on the weight of the person. The bigger the person, the more caffeine (coffee) they need.
Some people are going to be affected more strongly than others just because of the variability in people. Just like some people have bigger noses, also some people are more sensitive to caffeine.
Caffeine on average is probably "better" or safer for young adults rather than old people because it can cause heart and other problems in old people. Children should not take too much caffeine. It is addictive. People get addicted to caffeine and their bodies get "tolerant" which means after a while it takes more caffeine to get the desired effect. So people who don't use coffee regularly will feel the effect more from a single dose, than people who use it regularly.
By the way, all these facts apply to tea or coca cola, or any drink that contains caffeine, not just coffee. Find out more about caffeine at the Health Canada website.
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