Caffeine The addition of caffeine into a product is to appeal to the consumer as a stimulant. Stimulants help keep people awake and alert. However, overconsumption of caffeinated products can cause jitteriness and affect calcium metabolism. Many theories of why caffeine is an addicting stimulant point to the â€œdrugâ€™sâ€� interference with the hormone adenosine, which tells the body that it needs to sleep. Without catching up on the sleep deprived by caffeine, the human body will not function at its best in performing physically and mentally. Interestingly enough the ingredient guarana is caffeine. It is a woody vine native to Brazil and is commonly seen in energy drinks, protein bars, and weight-loss products. If caffeine and guarana are listed under the food label, it means the caffeine has two sources. Caffeine is still a stimulant and has the same effects no matter what source it came from naturally or artificially. Reid, T.R. â€œSlurped in black coffee or sipped in green tea, gulped down in a soda or knocked back in a headache pill, caffeine is the world's most popular psychoactive drug.â€� National Geographic. Web. 17 May 2011.