Anorexia (deriving from the Greek "α(ν)-" (a(n)-, a prefix that denotes absence) + "όρεξη'' (orexe) = appetite) is the decreased sensation of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, there are many possible causes for a decreased appetite, some of which may be harmless while others pose significant risk for the person.
The most common form of anorexia is simply satiation following the consumption of food. This happens in all normal humans and is called postprandial anorexia. Disorders that cause (harmful) anorexia include anorexia nervosa, severe depression, cancer, Crohn's Disease, Ulcerative Colitis, dementia, AIDS, Superior Mesenteric Artery Syndrome, Acute Radiation Syndrome, and chronic renal failure and the use of certain drugs, particularly stimulants and narcotics such as cocaine and heroin. Abrupt cessation of appetite-increasing drugs, such as marijuana, can cause loss of appetite as well. Environmentally induced disorders such as altitude sickness can also trigger an acute form of anorexia. Anorexia may also be seen in congestive heart failure, perhaps due to congestion of the liver with venous blood.
Although the presenting symptom (the one which prompts a patient to seek medical attention) in acute appendicitis is abdominal pain, patients virtually always experience anorexia as well, possibly accompanied by an early episode of vomiting.
Some medications, antidepressants for example, can have anorexia as a side effect. Most notoriously, however, chemicals that are a member of the phenethylamine family are known to have more intense anorectic properties. For this reason, many individuals suffering from anorexia nervosa may seek to use these medications to suppress appetite. Such prescription medications include Ritalin, Adderall, Dexedrine, and Desoxyn. In some cases, these medications are prescribed to patients prior to undergoing an operation requiring general anesthesia. This is a prophylactic measure taken to ensure no food will back up into the esophagus and cause the patient to stop breathing during the procedure.