Synephrine is a group of chemicals that includes the compound p-synephrine which is found in the peel of the bitter orange (Citrus aurantium). p-Synephrine has a similar structure to ephedrine, adrenaline capsaicin (from chili peppers) and raspberry ketone (from Rubus Idaeus). However, p-synephrine does not possess the same pharmacological effects as ephedrine or adrenaline, and this relates to the fact that it is not able to activate the central nervous system and has slightly different receptor affinities. For example, ephedrine is able to bind to α-1, α-2, β-1, β-2 and β-3 adrenergic receptors, but p-synephrine only shows affinity for the β-3 receptor. This means that whilst no cardiovascular effects for p-synephrine are apparent, there is a thermogenic effect from the activation of the β-3 adrenergic receptor. This also means that p-synephrine is not a stimulant and it therefore loses some of the weight loss effects of ephedrine which include increased energy expenditure, increased activity levels and an appetite suppressant effect. p-Synephrine may also increase the cellular uptake of glucose to muscle cells and may stimulate glycolysis, gluconeogenesis and glycogenolysis. The thermogenic effects of p-synephrine appear to be enhanced by addition of naringin and hesperidin, two flavonoids present in citrus fruits.
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Stohs, S. J. and Badmaev, V. 2016. A review of natural stimulant and non‐stimulant thermogenic agents. Phytotherapy Research. 30(5): 732-740
