Nausea may be defined as an unpleasant sensation of the need to vomit.[3] It may be accompanied by symptoms such salivation, feeling faint, and a fast heart rate.[3] Vomiting is the forceful ejection of stomach contents through the mouth.[3] Although nausea and vomiting are closely related, some patients experience one symptom without the other and it may be easier to eliminate vomiting than nausea.[1] The vomiting reflex (also called emesis) is thought to have evolved in many animal species as a protective mechanism against ingested toxins. In humans, the vomiting response may be preceded by an unpleasant sensation termed nausea, but nausea may also occur without vomiting. The central nervous system is the primary site where a number of emetic stimuli (input) are received, processed and efferent signals (output) are generated as a response and sent to various effector organs or tissues, leading to processes that eventually end in vomiting.[9] The detection of emetic stimuli, the central processing by the brain and the resulting response by organs and tissues that lead to nausea and vomiting are referred to as the emetic pathway or emetic arch.