Synephrine, or, more specifically, p-synephrine, is analkaloid, occurring naturally in some plants and animals, as well as inapproved drugs products in form of its m-substituted analog known asneo-synephrine. p-synephrine (or formerly Sympatol and oxedrine [BAN]) andm-synephrine are known for their longer acting adrenergic effects compared to norepinephrine. This substance is present at very low concentrations in common food stuffs such as orange juice and other orange (Citrus species) products,both of the "sweet" and "bitter" variety. The preparations used in Traditional Chinese Medicine (TCM), also known as Zhi Shi, are the immature and dried whole oranges from Citrus aurantium (Fructus AurantiiImmaturus). Extracts of the same material or purified synephrine are also marketed in the US,sometimes in combination with caffeine, as a weight-loss-promoting dietary supplement for oral consumption. While the traditional preparations have been in use for millennia as a component of TCM-formulas, synephrine itself is notan approved OTC drug. As a pharmaceutical, m-synephrine is still used as asympathomimetic (i.e. for its hypertensive and vasoconstrictor properties),mostly as a parenteral drug in the treatment of emergencies such as shock andrarely p.o. for the treatment of bronchial problems associated with asthma and hay-fever.
In physical appearance,synephrine is a colorless, crystalline solid and is water-soluble. Its molecular structure is based on a phenethylamine skeleton, and is related to those of many other drugs, and to the major neurotransmitters epinephrine and norepinephrine.
Some dietary supplements, sold for the purposes of promoting weight-loss or providing energy, contain synephrine as one of several constituents. Usually, the synephrine is present as a natural component of Citrus aurantium ("bitter orange"), bound up in the plant matrix, but could also be of synthetic origin, or a purified phytochemical (i.e. extracted from a plant source and purified to chemical homogeneity).,The concentration range found by Santana and co-workers in five different supplements purchased in the US was about 5 – 14 mg/g.