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). Drugs
Stimulants, such as ephedrine, amphetamine, methamphetamine, MDMA, cathinone, methylphenidate, nicotine, cocaine, caffeine, etc. Narcotics, such as heroin, morphine, codeine, hydrocodone, oxycodone, etc. Antidepressants can have anorexia as a side effect, primarily selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine. Byetta, a type II diabetes drug, will cause moderate nausea and loss of appetite. Abruptly stopping appetite-increasing drugs, such as cannabis and corticosteroids. Chemicals that are members of the phenethylamine group. (Individuals with anorexia nervosa may seek them to suppress appetite.) Topiramate may cause anorexia 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.
Anorexia is a medical term for a loss of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a loss of appetite, some of which may be harmless, while others indicate a serious clinical condition or pose a significant risk. Anorexia is a symptom, not a diagnosis. Anorexia is not to be confused with the mental health disorder anorexia nervosa. Because the term anorexia is often used as a short-form of anorexia nervosa, to avoid confusion a provider must clarify to a patient whether they are simply referring to a decreased appetite or the  mental health disorder. Anyone can manifest anorexia as a loss of appetite, regardless of their gender, age, or weight. The symptom also occurs in other animals, such as cats, dogs, cattle, goats, and sheep. In these species, anorexia may be referred to as inappetence. As in humans, loss of appetite can be due to a range of diseases and conditions, as well as environmental and psychological factors. Etymology
The term is from Ancient Greek: ανορεξία (ἀν-, without + όρεξις, spelled órexis, meaning appetite). Common manifestations
Anorexia simply manifests as a decreased or loss of appetite. This can present as not feeling hungry or lacking the desire to eat. Sometimes people do not even notice they lack an appetite until they begin to lose weight from eating less. In other cases, it can be more noticeable, such as when a person becomes nauseated from just the thought of eating.