Bitter orange, Seville orange, sour orange, bigarade orange, or marmalade orange is the citrus tree Citrus × aurantium and its fruit. It is native to Southeast Asia and has been spread by humans to many parts of the world. It is probably a cross between the pomelo, Citrus maxima, and the mandarin orange, Citrus reticulata
The extract of bitter orange (and bitter orange peel) has been marketed as dietary supplement purported to act as a weight-loss aid and appetite suppressant. Bitter orange contains the tyramine metabolites N-methyltyramine, octopamine, and synephrine, substances similar to epinephrine, which act on the α1 adrenergic receptor to constrict blood vessels and increase blood pressure and heart rate. Several low-quality clinical trials have had results of p-synephrine (alone or in combination with caffeine or some other substances) increasing weight loss slightly.