Arabica beans generally produce a more full-bodied flavor. These beans are the ones likely to be found in gourmet coffee shops. The roasting and brewing of coffee also play a part. Contrary to popular belief, darker roasted beans actually have less caffeine. The heat literally roasts out the caffeine.
Caffeine acts as a stimulant on the central nervous system.
That means it increases the heart rate and blood pressure. The individual may temporarily feel more awake and energetic. Caffeine also acts as a diuretic, which means it works on the kidneys to excrete more urine. Someone who wants to stop drinking caffeine should start by mixing regular coffee with a decaffeinated version. It's helpful to gradually reduce the amount of caffeine ingested each day.