<unk> , or, more specifically, p-synephrine, is an alkaloid, occurring naturally in some plants and animals, and also in approved drugs products as its m-substituted analog known as neo-synephrine. p-synephrine (or formerly Sympatol and oxedrine [BAN]) and m-synephrine are known for their longer acting adrenergic effects compared to norepinephrine. This substance is present at very low concentrations in common foodstuffs 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 Aurantii Immaturus). Extracts of the same material or purified<unk>  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,<unk>  itself is not an approved OTC drug. As a pharmaceutical, m-synephrine is still used as a sympathomimetic (i.e. for its hypertensive and vasoconstrictor properties), mostly by injection for the treatment of emergencies such as shock, and rarely orally for the treatment of bronchial problems associated with asthma and hay-fever.[lower-alpha 1]
It is important to distinguish between studies concerning<unk>  as a single chemical entity (and even here it should be borne in mind that<unk>  can exist in the form of either of two stereoisomers, d- and l-synephrine, which are chemically and pharmacologically distinct), and<unk>  which is mixed with other drugs and/or botanical extracts in a "Supplement", as well as<unk>  which is present as only one chemical component in a naturally-occurring mixture of phytochemicals such as the rind or fruit of a bitter orange. Mixtures containing<unk>  as only one of their chemical components (regardless of whether these are of synthetic or natural origin) should not be assumed to produce exactly the same biological effects as<unk>  alone.
In physical appearance,<unk>  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.
Synephrine
Norepinephrine
Dopamine
Octopamine
Aldosterone
Angiotensin II 
Angiotensinamide
Hyoscyamine