Synephrine is the main "active" compound found in the fruit of a plant called Citrus aurantium. The fruit is also known as zhi shi (in traditional Chinese medicine), and as green orange, sour orange and bitter orange in other parts of the world. Synephrine is chemically very similar to the ephedrine and pseudo-ephedrine found in many OTC cold/allergy medications and in a number of weight loss and energy supplements which contain Ma Huang. Because synephrine is a stimulant, similar to caffeine and ephedrine, it is thought to have similar effects in terms of providing an energy boost, suppressing appetite and increasing metabolic rate and caloric expenditure. In traditional Chinese medicine (TCM), zhi shi is used to help stimulate the Qi (energy force). Although synephrine and several other compounds found in zhi shi are structurally similar to ephedrine and are known to act as stimulants (via adrenergic activity), zhi shi does not appear to have the same negative central nervous effects of ma huang (ephedra). Through its stimulation of specific adrenergic receptors (beta-3, but not beta-1, beta-2 or alpha-1), zhi shi is theorized to stimulate fat metabolism without the negative cardiovascular side effects experienced by some people with Ma Huang.