Determination of Synephrine and Caffeine in Citrus Species Herbal Medicines and Weight-Loss Supplements from Taiwan by High-Performance Liquid Chromatography (HPLC)

Synephrine is widely found in Chinese herbs of the Rutaceae family and is commonly used as a primary substitute for ephedrine in sports supplements. However, its potential cardiotoxicity has necessitated governmental regulations regarding its use. This study determined the contents of synephrine, phenylephrine, and caffeine in 30 Chinese herbal preparations (including five single herbs) and 16 supplements promoted for weight loss. The presence of naturally occurring synephrine was detected in all Chinese herbal medicines, with immature bitter orange having the highest synephrine content (ranging from 233.1 to 505.3 mg/100 g). This was followed by three herbs with comparable amounts of up to 317.7 mg/100 g, namely bitter orange, red tangerine exocarp, and tangerine peel. Euodia fruit had the lowest synephrine content, measuring up to 4.9 mg/100 g. None of these herbal medicines were found to contain detectable phenylephrine. On the other hand, weight-loss supplements, comprising complex combinations of herbal extracts, were found to contain synephrine in concentrations up to 1159.0 mg/100 g and caffeine up to 1659.1 mg/100 g. The synephrine content of these products did not exceed the regulatory limit of six percent, nor did they surpass the respective daily consumption of 20 mg. However, one product was found to contain both synephrine and caffeine, albeit at low concentrations, which could potentially breach the regulation prohibiting the combined use of bitter orange and caffeine as food ingredients.