All Diseases

Nicotine dependence — also called tobacco dependence — is an addiction to tobacco products caused by the drug nicotine. Nicotine dependence means you can't stop using the substance, even though it's causing you harm.

Nicotine produces physical and mood-altering effects in your brain that are temporarily pleasing. These effects make you want to use tobacco and lead to dependence. At the same time, stopping tobacco use causes withdrawal symptoms, including irritability and anxiety.

While it's the nicotine in tobacco that causes nicotine dependence, the toxic effects of tobacco result from other substances in tobacco. Smokers have much higher rates of heart disease, stroke and cancer than nonsmokers do.

Regardless of how long you've smoked, stopping smoking can improve your health. Many effective treatments for nicotine dependence are available to help you manage withdrawal and stop smoking for good. Ask your doctor for help.

A nightmare is a disturbing dream associated with negative feelings, such as anxiety or fear. Nightmares are common, and occasional nightmares usually are nothing to worry about. However, they may become a problem if you have them often and they disrupt your sleep or cause you to fear going to sleep. A diagnosis of nightmare disorder is only made if nightmares cause ongoing distress or problems with daytime functioning.

Nightmares may begin in children between 3 and 6 years old and tend to decrease after about age 10. Until age 13, boys and girls appear to have nightmares in equal numbers. At age 13, nightmares seem to be more prevalent in girls than boys. Some people have them as teens or adults or throughout their lives.

Non-Hodgkin's lymphoma, also called non-Hodgkin lymphoma, is cancer that originates in your lymphatic system, the disease-fighting network spread throughout your body. In non-Hodgkin's lymphoma, tumors develop from lymphocytes — a type of white blood cell.

Non-Hodgkin's lymphoma is more common than the other general type of lymphoma — Hodgkin lymphoma.

Many different subtypes of non-Hodgkin's lymphoma exist. The most common non-Hodgkin's lymphoma subtypes include diffuse large B-cell lymphoma and follicular lymphoma.

Nonalcoholic fatty liver disease is a term used to describe the accumulation of fat in the liver of people who drink little or no alcohol.

Nonalcoholic fatty liver disease is common and, for most people, causes no signs and symptoms and no complications.

But in some people with nonalcoholic fatty liver disease, the fat that accumulates can cause inflammation and scarring in the liver. This more serious form of nonalcoholic fatty liver disease is sometimes called nonalcoholic steatohepatitis.

At its most severe, nonalcoholic fatty liver disease can progress to liver failure.

Nonallergic rhinitis involves chronic sneezing or having a congested, drippy nose with no apparent cause. The symptoms of nonallergic rhinitis are similar to those of hay fever (allergic rhinitis), but there's no identified allergic reaction involved. Nonallergic rhinitis can affect children and adults, but is more common after age 20.

Although nonallergic rhinitis is more annoying than harmful, it can make you miserable. Triggers of nonallergic rhinitis symptoms vary and can include certain odors or irritants in the air, changes in the weather, some medications, certain foods, and chronic health conditions. A diagnosis of nonallergic rhinitis is made after an allergic cause is ruled out. This may require allergy skin or blood tests.

Nonulcer stomach pain is a term used to describe signs and symptoms of indigestion that have no obvious cause. Nonulcer stomach pain is also called functional dyspepsia (dis-PEP-see-uh) or nonulcer dyspepsia.

Nonulcer stomach pain is common and can be long lasting. Nonulcer stomach pain can cause signs and symptoms that resemble those of an ulcer, such as pain or discomfort in your upper abdomen, often accompanied by bloating, belching and nausea.

Noonan syndrome is a genetic disorder that prevents normal development in various parts of the body. A person can be affected by Noonan syndrome in various ways. These include unusual facial characteristics, short stature, heart defects, other physical problems and possible developmental delays.

Noonan syndrome is caused by a genetic mutation and is acquired when a child inherits a copy of an affected gene from a parent (dominant inheritance). It can also occur as a spontaneous mutation, meaning there's no family history involved.

There's no specific treatment for Noonan syndrome. Management focuses on controlling the disease's symptoms and complications. Growth hormone may be used to treat short stature in some people with Noonan syndrome.

Norovirus infection can cause the sudden onset of severe vomiting and diarrhea. The virus is highly contagious and commonly spread through food or water that is contaminated by fecal matter during preparation. You can also be infected through close contact with an infected person.

Diarrhea, abdominal pain and vomiting typically begin 24 to 48 hours after exposure. Norovirus symptoms last one to three days, and most people recover completely without treatment. However, for some people — especially infants, older adults and people with underlying disease — vomiting and diarrhea can be severely dehydrating and require medical attention.

Norovirus infection occurs most frequently in closed and crowded environments such as hospitals, nursing homes, schools and cruise ships.

Obesity is a complex disorder involving an excessive amount of body fat. Obesity isn't just a cosmetic concern. It increases your risk of diseases and health problems such as heart disease, diabetes and high blood pressure.

Being extremely obese means you are especially likely to have health problems related to your weight.

The good news is that even modest weight loss can improve or prevent the health problems associated with obesity. Dietary changes, increased physical activity and behavior changes can help you lose weight. Prescription medications or weight-loss surgery also may be options for treating obesity.

Obsessive-compulsive disorder (OCD) is characterized by unreasonable thoughts and fears (obsessions) that lead you to do repetitive behaviors (compulsions). It's also possible to have only obsessions or only compulsions and still have OCD.

With OCD, you may or may not realize that your obsessions aren't reasonable, and you may try to ignore them or stop them. But that only increases your distress and anxiety. Ultimately, you feel driven to perform compulsive acts in an effort to ease your stressful feelings.

OCD often centers around themes, such as a fear of getting contaminated by germs. To ease your contamination fears, you may compulsively wash your hands until they're sore and chapped. Despite efforts to ignore or get rid of bothersome thoughts, the thoughts or urges keep coming back. This leads to more ritualistic behavior — and a vicious cycle that's characteristic of OCD.