Thread: Synephrine hcl

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Ephedrine vs. Synephrine
By Alan E. Shugarman, MS, RD

This information was published in Flex Magazine, October 1999 issue, in the Advanced Nutrition section.

Since very little published research compares supplementation of ephedrine to synephrine in lean individuals, I set up a study at the University of Utah that compared these two compounds to one another as well as to a placebo. The test formulations contained either 24 milligrams (mg) of ephedrine or 10 mg of synephrine. These are the common supplement industry dosages of ephedrine and synephrine.
Both formulas also included 300 mg of caffeine, 12 mg of yohimbe and 200 mg of quercetin.The synephrine mixture also contained 50 mg of Scizonopeta tenuifolla and Ledebouriella divaricata, two Chinese herbs known to produce a warming effect. The study was a double blind, placebo controlled crossover design, and used 20 young healthy subjects, 10 men and 10 women. Resting metabolic rate, respiratory exchange ration, body care temperature, heart rate and blood pressure were measured.
Resting metabolic rate increased significantly with the ephedrine mix versus placebo. The synephrine formula did not significantly elevate resting metabolic rate for any one 15 minute period during the 195 minutes of measurement.

However, by crudely extrapolating the 195 minutes of collected data over a 24 hour period, both the ephedrine and synephrine formulations showed a significant increase in total resting metabolic rate when compared to the placebo. Respiratory exchange ration decreased significantly toward fat burning with only the ephedrine formulation versus placebo. Body core temperature increased greatly with both the ephedrine and the synephrine formulas compared to the placebo. Heart rate was elevated considerably with the ephedrine versus placebo, but not with the synephrine. Blood pressure was elevated significantly following both formulations versus the placebo.

The bottom line here is that although the synephrine formulation seemed to have a mild effect, the ephedrine formulation outperformed synephrine across the board for elevating metabolic rate and shifting respiratory exchange ration toward fat burning. When you compare a synephrine based mixture to an ephedrine based one for fat burning potential, the ephedrine formulations appear to have the edge, based on available research.

Synephrine and ephedrine act differently upon alpha and beta adrenergic receptor sites. Ephedrine is an indirect and direct acting beta agonist with relatively slight activation of the alpha receptors; synephrine is a direct acting alpha agonist with relatively slight activation of beta receptors, via release of norepinephrine and epinephrine. This is important when attempting to determine the potential for fat burning, because the bottom line is that beta receptors, especially beta-3 receptors, are the key to burning fat.


Admittedly, in this study, the dosage of ephedrine and synephrine in each formulation was not equivalent, so these data cannot be considered conclusive; however, those who tout synephrine as superior to ephedrine for the purpose of getting lean are reaching for data that are not in evidence. Direct comparison studies using the same dosage of both ephedrine and synephrine are still needed. At this point, ephedrine has the edge, both in the scientific literature and in the gym, when it comes to fat burning ability.