Synephrine is an ingredient in some diet supplements. It is a stimulant that is quite similar to ephedrine and caffeine since it provides an energy boost while increasing metabolism and suppressing the appetite. Synephrine is generally considered a safer alternative to Ma Huang and ephedrine. It is advertised to stimulate the metabolism of fat cells without all the side effects of other stimulants such as higher blood pressure and the jitters.
Those that use synephrine claim a myriad of benefits. This can include increasing metabolic rates, an increase of caloric expenditure (the quickness in which you lose calories), increasing of energy levels, as well as synephrine acting as a fat burner and as a promoter of weight loss.
The theory is that because synephrine acts as a stimulant, much like caffeine, it is believed to have some of the same effects in terms of an energy boost. In Chinese medicine, zhi shi is used to help stimulate energy. While synephrine and many of the components that can be found in zhi shi appear to be the same as the ones found in ephedrine, synephrine is believed to work as a stimulant without leaving the negative side effects that inflict the central nervous system like ephedra does. synephrine differs from ephedrine in that synephrine is considered a semi-selective sympathomimetic (because it targets some tissues such as fat, more than it targets others such as the heart) versus a non-selective sympathomimetic (like ephedra which targets many tissues equally and thus often causes side effects). For example, although some high-dose ephedra-containing supplements have been associated with certain cardiovascular side effects as elevated blood pressure and heart palpitations, researchers at Mercer University in Atlanta have shown that Citrus aurantium extract (because it targets fat tissue rather than heart tissue) has no effect on hemodynamics such as heart rate and blood pressure.
A recent study conducted in dogs suggests that synephrine and octopamine can increase metabolic rate in a specific type of fat tissue known as brown adipose tissue (BAT). This effect would be expected to increase fat loss in humans – except for one small detail – adult humans don’t have brown adipose tissue to speak of.