Some physiology
Vomiting is a protective mechanism for eliminating irritant or harmful substances for the upper gastrointestinal tract. The act of emesis is controlled by the vomiting centre in the medulla and respiration, salivation and vascular control which give rise to the prodromal sensations of vomiting. The vomiting centre does not initiate, but rather it coordinates the act of emesis on receiving stimuli from various sources, namely,
initiate