Another Study Finds Bitter Orange Safe

The use of bitter orange extract and p-synephrine appears to be “exceedingly safe," according to a new review of current information regarding the safety of Citrus aurantium (bitter orange) extract and p-synephrine based on human, animal and in vitro assessments as well as receptor binding and mechanistic studies (Phytother Res. 2011 Apr 8. DOI: 10.1002/ptr.3490).

The review found in 89 clinical research studies, no serious adverse effects were directly attributable to bitter orange extract and its principal protoalkaloidal constituent p-synephrine.

Researchers Sidney J. Stohs, Ph.D., and Harry G. Preuss, M.D. in conjunction with Mohd Shara, Pharm.D., Ph.D., concluded, the "preponderance of human clinical studies have reported that bitter orange extract (p-synephrine) either alone or in combination with caffeine and other ingredients has no effect on blood pressure or heart rate."

Despite questions that are frequently raised regarding the safety of these ingredients, they noted millions of doses of weight-loss, weight-management and sports-performance dietary supplements have been consumed by possibly millions of individuals in recent years, and further, millions of people consume various juices and food products from citrus species that contain p-synephrine on a daily basis.

This summary contains a detailed discussion of p-synephrine receptor binding and the reasons for the absence of negative cardiovascular side effects. It reports 19 separate analytical studies determined that m-synephrine was not present among the protoalkaloids of bitter orange. m-Synephrine (phenylephrine), which is often found in nasal decongestants and sprays, has the potential for raising blood pressure in humans.

The researchers also clarify a study that is frequently cited as evidence of adverse cardiovascular effects: Hemodynamic Effects of Ephedra-Free Weight-Loss Supplements in Humans - Haller, et al. (September 2005). Stohs, et al., point out that Haller’s study clearly supports bitter orange’s safety. Haller reported that no significant effects on heart rate were recorded for three hours after subjects ingested two different the dietary supplements, one of which contained bitter orange. An increase in heart rate occurred only at the six-hour mark, after all subjects had consumed a meal.

"After eating, an increase in heart rate occurred in the two treatment groups as well as in the control group. The increase in heart rate does not coincide with the pharmacokinetics including blood levels and half-life of p-synephrine (Haller, et al., 2005, 2008) but does coincide with the thermic effect of food (Gougeon, et al., 2005)," wrote Stohs, et al.

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