p-Synephrine: an overview of physicochemical properties, toxicity, biological and pharmacological activity.

p-Synephrine is a popular ingredient in dietary supplements. It is also found in trace amounts in living organisms. It is advertised as a weight loss supplement and it is supposed to improve performance in sports. It is contained in plants of the Citrus family, making it widespread in the human diet. Its pharmacological properties include effects on multiple receptors and signaling pathways. Its effects on the alpha and betanergic systems promote doubts about its safety. There are many studies describing a lack of concern when it comes to the potential harmful effects of this compound. On the other hand, several health incidents associated with p-synephrine use have been reported in the scientific literature, making the toxicity of this compound unclear. This review aims to organize the current knowledge about p-synephrine, including physicochemical characteristics, sources of occurrence, pharmacological effects and possible toxic effects. In addition, the presence of three substitution isomers of the hydroxyl group and one chiral carbon atom causes confusion in the literature. Studies conducted on the short-term use of p-synephrine do not indicate its toxicity at low doses for healthy people. Further studies are needed to determine its long-term safety and possible interactions with other chemical compounds. See also the graphical abstract(Fig. 1).