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Vomiting is the term used to describe the forced expulsion of gastric contents. It differs from retching, in so far as retching occurs in the absence of such expulsion. Vomiting is sometimes confused with regurgitation which describes the return of oesophageal contents to the mouth, as occurs in gastro-oesophageal reflux disease. Vomiting is a reflex which allows people to rid themselves of noxious chemicals or infections which they have ingested. Vomiting is triggered by stimulation of the vomiting centre in the medulla, either by activation from the gut whence ascending nerve fibres arise to the vomiting centre,  from the cerebral cortex (the upper part of the brain, which is responsible for thinking and intentional movement) or other parts of the brain, such as the limbic system which is responsible for our emotional response, where a variety of stimuli can trigger vomiting, or as a result of noxious chemicals directly effecting the chemo-receptor trigger zone, which is closely linked to the vomiting centre in the medulla.

Gastrointestinal stimuli include infection, gastro-intestinal inflammation (gastritis, gastric or duodenal ulcers), pancreatitis, malignancy (gastric cancer) and gut ischaemia. Systemic disease, including infections, endocrine disease, such as hyperthyroidism, diabetic ketoacidosis and hypercalcaemia all of which may have effects on motility, microbiome and appetite that trigger vomiting. Disease of the central nervous system, including anxiety, raised intracranial pressure, encephalitis and psychiatric disease may also trigger nausea. Toxins, such as chemotherapy, drugs, and other chemicals may trigger nausea via directly stimulating the chemoreceptor trigger zone.

In general it is important to identify the cause of vomiting in tandem with treating the symtpoms and their effects, such as dehydration and disturbance of the balance of salts within the blood. On occasion the cause is clear, for example where a family have eaten out and then rapidly developed gastroenteritis, however often the causes are multi-factorial, reflecting the complexity of interacting triggers that feed into the vomiting centre. For example patients receiving chemotherapy, which is known to cause nausea may develop anticipatory nausea prior to receiving chemotherapy, clearly in this context psychological factors as well as “toxic” chemicals may influence the development of symptoms. When symptoms are more long-term (chronic) healthcare professionals will try to exclude structural problems by exploring the history and examing patients to elicit clues as to the likely aetiology (causes). They may also undertake a number of investigations to exclude structural or sinister problems, such as endoscopy, scanning, or blood testing.

Treatment of vomiting is focused on identifying and treating the underlying causes whilst correcting the consequences if and when they arise (weight loss, metabolic abnormalities dehydration). Many patients with vomiting have a number of different but interrelated triggers. Whilst these are addressed healthcare professionals often use a variety of drugs to treat the symptoms of nausea and vomiting. These are known as anti-emetics and have a range of effects on several of the triggers of nausea and vomiting.

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