With the exception of caffeine, none of these nutrients is found in coffee. Coffee's best known constituent is the methylxanthine central nervous system stimulant caffeine. How much caffeine you get in a cup of coffee depends on how the coffee was processed and brewed. Caffeine is water-soluble. Instant, freeze-dried, and decaffeinated coffees all have less caffeine than plain ground roasted coffee.
Caffeine is a stimulant.
It increases alertness and concentration, intensifies muscle responses, quickens heartbeat, and elevates mood. As a rule, it takes five to six hours to metabolise and excrete caffeine from the body. During that time, its effects may vary widely from person to person. Some find its stimulation pleasant, even relaxing, others experience restlessness, nervousness, hyperactivity, insomnia, flushing, and upset stomach after as little as one cup a day. It is possible to develop a tolerance for caffeine, so people who drink coffee every day are likely to find it less immediately stimulating than those who drink it only once in a while.