Nausea (Latin nausea, from Greek ναυσία - nausia, "ναυτία" - nautia, motion sickness", "feeling sick," "queasy" or "wamble") is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting. A person can suffer nausea without vomiting. (Greek ναῦς - naus, "ship"; ναυσία started as meaning "seasickness".)
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, gastroenteritis (stomach infection) or food poisoning. Side effects of many medications including cancer chemotherapy, nauseants or morning sickness in early pregnancy. Nausea may also be caused by anxiety, disgust and depression.
There are many causes of nausea. One organization listed 700 in 2009. Gastrointestinal infections (37%) and food poisoning are the two most common causes. Side effects from medications (3%) and pregnancy are also relatively frequent. In 10% of people the cause remains unknown.
Food poisoning usually causes an abrupt onset of nausea and vomiting one to six hours after ingestion of contaminated food and lasts for one to two days. It is due to toxins produced by bacteria in food.
Nausea or "morning sickness" is common during early pregnancy but may occasionally continue into the second and third trimesters. In the first trimester nearly 80% of women have some degree of nausea. Pregnancy should therefore be considered as a possible cause of nausea in any women of child bearing age. While usually it is mild and self-limiting severe cases known as hyperemesis gravidarum may require treatment.
Stress and depression
While most causes of nausea are not serious, some serious causes do occur. These include: diabetic ketoacidosis, brain tumor, surgical problems, heart attack, pancreatitis, small bowel obstruction, meningitis, appendicitis, cholecystitis, Addisonian crisis, Choledocholithiasis (from gallstones) and hepatitis, as a sign of carbon monoxide poison and many others.
If dehydration is present due to loss of fluids from severe vomiting, rehydration with oral electrolyte solutions is preferred. If this is not effective or possible, intravenous rehydration may be required. NIH Medline recommends drinking clear fluids, sitting quietly and eating bland foods.  Medline recommends you call a doctor if you:
- Cannot keep any food or liquid down
- Vomit 3 or more times in 1 day
- Are nauseated for more than 48 hours
- Feel weakness
- Have fever
- Have stomach pain
- Do not have to urinate for 8 hours or more 
Dimenhydrinate (Gravol) is an inexpensive and effective over the counter medication for preventing postoperative nausea and vomiting. Meclozine is another antihistamine antiemetic. In certain people, cannabinoids may be effective in reducing chemotherapy associated nausea and vomiting. Ondansetron (Zofran) is effective for nausea and vomiting. Pyridoxine or metoclopramide are the first line treatments for pregnancy related nausea and vomiting. Many consider Medical marijuana to be an effective herbal remedy for nausea, where legal.
In hospital settings topical anti-nausea gels are not indicated because of lack of research backing their efficacy. Topical gels containing lorazepam, diphenhydramine, and haloperidol are sometimes used for nausea but are not equivalent to more established therapies.
While short-term nausea and vomiting are generally harmless, they may sometimes indicate a more serious condition. When associated with prolonged vomiting, it may lead to dehydration and/or dangerous electrolyte imbalances. Repeated intentional vomiting, characteristic of bulimia, can cause stomach acid to wear away at the enamel in teeth.
Nausea and or vomiting is the main complaint in 1.6% of visits to family physicians in Australia. However only 25% of people with nausea visit their family physician. It is most common in those 15–24 years old and less common in other ages.
- ναυσία, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
- ναυτία, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
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