According to the National Center for Biotechnology Information, caffeine is the most used central nervous system stimulant. MedlinePlus states that caffeine stimulates the nervous system, making the consumer feel alert and sometimes jittery.
According to Medline Plus, too much caffeine causes problems such as headaches, dizziness, dehydration and abnormal heart rhythms. Heavy usage creates health issues such as insomnia, irritability and muscle tremors, according to the Mayo Clinic. However, not all of caffeine's side effects are negative. Moderate amounts of caffeine have been shown to enhance physical and cognitive performance, increase the amount of energy available each day, enhance short term memory and decrease fatigue, alongside a lengthy list of other benefits.