Caffeine is a psychoactive stimulant drug and specifically, in humans, it is a central nervous system (CNS) stimulant, which temporarily restores alertness, helping people feel more awake and focused. Caffeine is found in varying quantities in certain beans, leaves, and fruit of some plants. Beverages such as coffee, tea, soft drinks, and energy drinks also contain caffeine. Caffeine is also a self-limiting stimulant, since it acts on the kidneys to increase the rate of its own excretion.

Caffeine has both positive and negative effects on human health, as has been concluded by various researches worldwide. Recent researches have found a definite and well-supported correlation between cardiac disease and the consumption of caffeine. Increased central nervous system activity can at times cause blood vessel constriction, which may increase blood pressure and threaten the proper supply of blood to the heart. In fact, most of the dangerous effects of strong stimulants like cocaine and methamphetamine are a direct result of their activity on blood vessels and the heart.

Evidence has repeatedly shown that consumption of caffeine increases the risk of high blood pressure, heart disease or heart attack but only slightly and the complications arising from it are short-term. However, some studies have also showed that the caffeine-blood pressure relationship may be more complicated than expected.