Nausea is an unpleasant, diffuse sensation of unease and discomfort, often perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged, and has been described as placing discomfort on the chest, upper abdomen, or back of the throat.Like pain, the purpose of nausea is to discourage the person or animal from repeating whatever caused the unpleasantness. The memory of pain elicits safer or evasive actions; the memory of nausea elicits revulsion towards whatever was eaten before vomiting it up — even if it was not the cause of the nausea.Nausea is a non-specific symptom, which means that it has many possible causes. Some common causes of nausea are motion sickness, dizziness, migraine, fainting, low blood sugar, gastroenteritis (stomach infection) or food poisoning. Nausea is a side effect of many medications including chemotherapy, or morning sickness in early pregnancy. Nausea may also be caused by anxiety, disgust and depression.Medications taken to prevent and treat nausea are called antiemetics. The most commonly prescribed antiemetics in the US are promethazine, metoclopramide and the newer, extremely effective ondansetron. The word nausea is from Latin nausea, from Greek ναυσία – nausia, "ναυτία" – nautia, motion sickness, "feeling sick or queasy".