Bitter orange, Seville orange, sour orange, bigarade orange, or marmalade orange refers to a citrus tree (Citrus × aurantium) and its fruit. It is hybrid between Citrus maxima (pomelo) and Citrus reticulata (mandarin). Many varieties of bitter orange are used for their essential oil, which is used in perfume, as a flavoring and as a solvent. The Seville orange variety is used in the production of marmalade. Bitter orange is also employed in herbal medicine as a stimulant and appetite suppressant, due to its active ingredient, synephrine. Bitter orange supplements have been linked to a number of serious side effects and deaths, and consumer groups advocate avoiding medicinal use of the fruit.