Caffeine is a CNS stimulant. Many people rely on a cup of coffee to wake them up for work and studies. Soon brain builds tolerance to the quantity of caffeine used every day. Now the person increases the quantity. This practice leads to addiction. After consuming a cup of coffee, caffeine absorbs into blood and passes blood brain barrier entering the brain. Caffeine blocks adenosine receptors and stimulates a surge of dopamine releasing alert signals to brain and body. Brain stimulates adrenal gland to produce adrenaline which adds more alertness. Over time, brain develops more adenosine receptors and to combat then more caffeine is required. This is how tolerance builds and a person consumes more and more caffeine. American Psychiatric Association (APA) does not currently identify Caffeine addiction as a Substance Use Disorder (SUD). However, it does recognize Caffeine withdrawal as a clinical condition. The World Health Organization (WHO) became the first medical corporation to formally recognize Caffeine addiction as a clinical disorder in 2012.