Ginger

The part of ginger usually used is technically a rhizome (an underground stem) but it is normally referred to as ginger root.
Ginger contains up to 3% of an essential oil that causes the fragrance of the spice. The main constituents of ginger oil are sesquiterpenoids with (-)-zingiberene as the main component. Lesser amounts of other sesquiterpenoids (ß-sesquiphellandrene, bisabolene and farnesene) and a small monoterpenoid fraction (ß-phelladrene, cineol, and citral) have also been identified.
The pungent taste of ginger is due to nonvolatile phenylpropanoid-derived compounds, particularly gingerols and shogaols. The latter are formed from the former when ginger is dried or cooked. Zingerone is also produced from gingerols during this process, and it is less pungent and has a spicy-sweet aroma.
Ginger has a sialagogue action, stimulating the production of saliva.
The medical form of ginger historically was called "Jamaica ginger"; it was classified as a stimulant and carminative, and used frequently for dyspepsia and colic. It was also frequently employed to disguise the taste of medicines. Ginger is on the American FDA's 'generally recognized as safe' list, though it does interact with some medications, including warfarin. Ginger is contraindicated in people suffering from gallstones as the herb promotes the release of bile from the gallbladder. Ginger may also decrease joint pain from arthritis, though studies on this have been inconsistent, and may have blood thinning and cholesterol lowering properties that may make it useful for treating heart disease. Its blood thinning properties, however, mean that anyone taking anticoagulants should take ginger only after medical advice.
The characteristic odour and flavour of ginger root are caused by a mixture of zingerone, shoagoles and gingerols, volatile oils that compose about one to three percent of the weight of fresh ginger. In laboratory animals, the gingerols increase the motility of the gastrointestinal tract and have analgesic, sedative, antipyretic and antibacterial properties.
Ginger compounds are active against a form of diarrhoea which is the leading cause of infant death in developing countries. Zingerone is likely to be the active constituent against enterotoxigenic Escherichia coli heat-labile enterotoxin-induced diarrhea.
Ginger has been found effective by multiple studies for treating nausea caused by seasickness, morning sickness and chemotherapy, though ginger was not found superior over a placebo for post-operative nausea.