Caffeine is the most consumed stimulant globally. It is consumed in the form of coffee and tea. At present there is no scientific data for promoting or discouraging coffee and or tea consumption in the daily diet. Short term benefits include mental alertness and improved athletic performance. Short term adverse effects including headache anxiety tremors and insomnia. Long term adverse effects include generalized anxiety disorder and substance abuse disorders. Long term benefits are dose dependent. Caffeine is associated with a reduced risk of Parkinson disease Alzheimer disease alcoholic cirrhosis and gout. Both caffeinated and decaffeinated coffee are also associated with a lower risk of type 2 diabetes. Heavy coffee intake may trigger coronary and arrhythmic events in susceptible individuals although coffee intake is not considered a long term risk factor for myocardial disease. Most studies show a modest inverse relationship between coffee consumption and all cause mortality. Caffeine withdrawal is a well documented clinical syndrome with headache being the most common symptom. Source Uptodate