Anorexia is the decreased sensation of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a decreased appetite, some of which may be harmless, while others indicate a serious clinical condition or pose a significant risk.
For example, anorexia of infection is part of the acute phase response (APR) to infection. The APR can be triggered by lipopolysaccharides and peptidoglycans from bacterial cell walls, bacterial DNA, and double-stranded viral RNA, and viral glycoproteins, which can trigger production of a variety of proinflammatory cytokines. These can have an indirect effect on appetite by a number of means, including peripheral afferents from their sites of production in the body, by enhancing production of leptin from fat stores. Inflammatory cytokines can also signal to the central nervous system more directly by specialized transport mechanisms through the blood–brain barrier, via circumventricular organs (which are outside the barrier), or by triggering production of eicosanoids in the endothelial cells of the brain vasculature. Ultimately the control of appetite by this mechanism is thought to be mediated by the same factors normally controlling appetite, such as neurotransmitters (serotonin, dopamine, histamine, norepinephrine, corticotropin releasing factor, neuropeptide Y, and α-melanocyte-stimulating hormone).
Acute radiation syndrome
Acute viral hepatitis
Addison's disease
Atypical pneumonia (mycoplasma)
AIDS
Anorexia nervosa
Anxiety disorder
Appendicitis
Cancer
Chronic pain
Chronic kidney disease
Congestive heart failure, perhaps due to congestion of the liver with venous blood
Crohn's disease
Dehydration
Dementia
Drug addiction
Hypervitaminosis D
Metabolic disorders, particularly urea cycle disorders
Mood disorders and the moods which arise from them, both depression and mania
Sickness behavior
Superior mesenteric artery syndrome
Tuberculosis
Thalassemia
Ulcerative colitis
Zinc deficiency
Amphetamine (Adderall), dextroamphetamine (Dexedrine & Dextrostat), lisdexamfetamine (Vyvanse)
Antidepressants can have anorexia as a side effect
Selective serotonin reuptake inhibitors
Byetta, a Type II Diabetes drug, will cause moderate nausea and loss of appetite
Dexmethylphenidate (Focalin)
Abrupt cessation of appetite-increasing drugs, such as cannabis and corticosteroids
Methamphetamine (Desoxyn) (treatment of ADHD and narcolepsy)
Methylphenidate (Ritalin & Concerta)
Chemicals that are members of the phenethylamine group. (Individuals with anorexia nervosa may seek them to suppress appetite)
Stimulants such as caffeine, nicotine, and cocaine
Topiramate (Topamax) (as a side effect)
Other drugs may be used to intentionally cause anorexia in order to help a patient preoperative fasting prior to general anesthesia. It is important to avoid food before surgery to mitigate the risk of pulmonary aspiration, which can be fatal.
Opiates act upon the digestive system and can reduce the physical sensation of hunger in the same way that they reduce physical sensations of pain. They also frequently cause delayed gastric emptying (gastroparesis) and can sometimes lead to changes in metabolism with long-term use.
During the post-operative recovery period for a tonsillectomy or adenoidectomy, it is common for adult patients to experience a lack of appetite until their throat significantly heals (usually between 10–14 days).
Altitude sickness
Significant emotional pain caused by an event (rather than a mental disorder) can cause an individual to temporarily lose all interest in food
Physical exercise
Experiencing grotesque or unappealing thoughts or conversations, or viewing similar images
Being in the presence of unappealing things such as waste matter, dead organisms, or bad smells
Anorexia is a relatively common condition that can lead patients to have dangerous electrolyte imbalances, leading to acquired long QT syndrome which can result in sudden cardiac death. This can develop over a prolonged period of time, and the risk is further heightened when feeding resumes after a period of abstaining from consumption. Care must be taken under such circumstances to avoid potentially fatal complications of refeeding syndrome.
