Vomiting is defined as the forceful expulsion of stomach or intestinal contents from the mouth, typically associated with contractions of the abdominal muscles and usually with symptoms of nausea.  It may occur with or without food in the stomach depending on the cause.  Vomiting is a symptom which can be a part of many conditions including infections, GI obstruction, motility problems, migraines, and many more.  Functional vomiting occurs when an individual has 1 or more episodes of vomiting per week that is not self-induced, due to chronic marijuana use, or caused by a central nervous system or metabolic condition.  This diagnosis is separate from another functional gastrointestinal syndrome, rumination, in which undigested food is effortlessly regurgitated minutes after eating and usually without associated nausea.
Vomiting