Tea leaf stands out among tea varieties with the bottom content of caffeine and high phenolic content. Caffeine a secondary metabolite present in tea, a mild central nervous system (CNS) stimulant that quickly boosts our alertness and energy levels. It has numerous pharmacological and biological effects, including cardiovascular, respiratory, renal and smooth muscle effects, as well as effects on mood, memory, attentiveness, and physical and cognitive performance. Caffeinated drinks (coffee and others) and tea are the foremost consumed, socially-acceptable stimulants within the world. In their natural forms tea contain several chemical components that may confer both beneficial and adverse health effects, Caffeine, a methylxanthine, is closely related to theophylline. Caffeine is speedily and fully absorbed from the GI tract. The volume of distribution in adults is approximately 0.5 L/kg. Caffeine is primarily metabolized by the cytochrome P450 (CYP) oxidase system in the liver. The plasma half-life of caffein varies significantly from person to person, with a mean half-life of 5-8 hours in healthy, non-smoking adults. Caffein clearance is accelerated in smokers; clearance is slowed in maternity, in liver disease and within the presence of some CYP inhibitors. Caffeine consumption has multiple general effects, involving the medical specialty, vessel, endocrine-metabolic, genitourinary and gastrointestinal systems. The impact on health is also changed by genetic factors, age, sex, medications, and different environmental exposures. Tea is that the second most well liked beverage globally once water and contains plenteous specialised metabolites. These metabolites provide tea distinctive quality and square measure helpful to human health. Some secondary metabolites are created to assist plants, as well as tea plants (Camellia sinensis) adapt to variable atmosphere and grow commonly. Therefore, whether or not abundant specialised metabolites have biological functions and play roles within the environmental adaptability of tea plants is of interest.