Functional is a diagnosis which describes the symptom of nausea associated with abnormal function of the nerves that both co-ordinate the stomach and those which perceive nausea and gastric distension within the peripheral and central nervous system, in the absence of a mechanical cause or an underlying pathology such as gastroparesis. Often there is a dysfunction of the co-ordination of foregut function by the nerves which control the relaxation of the upper part of the stomach (which normally allows the stomach to expand in response to eating) following ingestion of a meal (gastric or fundal accommodation) and, or the a failure to increase contractions at the lower end of the stomach in response to food arriving within it. Whilst it can be worse response to eating nausea can persist even between meals.

Often functional nausea may have an identifiable precipitating event such as a stressful period or an episode of gut infection. During stress it is normal for human beings to feel slightly nauseous or queasy (butterflies), this reflects a complex series of interaction between the environment, the central nervous and visceral (gut) nervous systems. The stomach acts as a reservoir for the food we have eaten, it holds food and gradually pushes it into the small bowel as the bowel is ready to disgest it. Usually food reaching the upper stomach during a meal  triggers a relaxation of the stomach (so you can accommodate more food) and an increase to the emptying of the stomach into the small bowel (to enable digestion and absorption to be completed) however in stressful circumstances, or when we are anxious, the stomach may fail to relax and increase its motility leading to early fullness and a sensation of nausea. This then triggers further responses which travel in part via the vagus nerve to the brain, where we perceive these changes. The brain can then trigger a series of secondary changes through its influence on the centres in the brain related to nausea (and vomiting), leading to further nausea. In people with functional nausea it is as if the brain and gut have become “Stuck” in a cycle where these responses persist leading to persistent and easily triggered nausea and sometimes retching.

It is important to try and recognise potential triggers and avoid them and where this is not possible to develop strategies to manage them. This may include psychological intervention and review of diet, exercise regimes and sleeping patterns which may all influence the cycle of persistent nausea .

Drugs to treat nausea may be effective at breaking the cycle but should be targeted at symptoms whilst underlying triggers are identified and managed. All of the anti-sickness drugs ave potential side-effects and many should not be used on a long term basis if at all possible.