Caffeine is a methylxanthine alkaloid with purine structure, it acts on the central nervous system (CNS). It is chemically related to adenine and guanine basis of DNA and RNA respectively. Caffeine containing drinks such as tea, coffee and cola are consumed globally in high volumes. Caffeine has both positive and negative health effects. It may have a small preventive effect against certain disorders including Parkinsons diseases. Some people experience sleep disruption or anxiety when they consume caffeine, also it can cause a moderate forms of drug dependence. This article focuses on the effect of caffeine in human body.