Introduction

Caffeine (1,3,7-trimethylxanthine) is a nitrogenous, organic compound, or alkaloid, which is associated with other physiological compounds such as nicotine, quinine and codeine.   Pure caffeine is a white and bitter-tasting crystal, which has a melting point of 235-237°C and sublimation occurs at 178°C.  Caffeine is soluble in hot water but less soluble in organic solvents (ethanol and ether).  After hydration and cooling, a monohydrate of the caffeine molecule is formed.

The amount of caffeine (mg) varies between different cups of coffee¹: 

Caffeine stimulates the central nervous system, heart, blood vessels and kidneys and can also increase the amount of urine passed through the body (diuretic).  Caffeine therefore decreases fatigue and has a positive impact on alertness.  However, negative effects of caffeine are irritability, insomnia, anxiety and headaches.  Decaffeinated products were introduced to prevent the intake of caffeine.

Other drinks also contain caffeine, here are just a few²: 

2 http://www.ask.co.uk/main/askjeeves.asp?ask=Caffeine&origin=