Bitter orange (Citrus auratium) is used in herbal medicine as a stimulant and appetite suppressant, due to its active ingredient, synephrine . Since ephedra (Ephedra sinica) was banned the sales of weight loss supplements like Citrus aurantium (bitter orange) has increased dramatically . Some experts believe that compounds contained in Citrus auratium may lead to weight loss.
Is synephrine effective for weight loss?
Some preliminary reports in animals noted significantly reduced food intake and body weight gain with Citrus auratium extract administration . Stephen Bend and colleagues  conducted a systematic review in 2004 in order to evaluate the efficacy of bitter orange extract which is marketed to promote weight loss. They managed to find only one eligible randomized placebo controlled trial, which lasted 6 weeks and was conducted on 20 patients. No statistically significant benefit for weight loss were noted.
Synephrine has the ability to interact with beta receptors, thereby promoting lipolysis  though it appears that it is poorly absorbed or rapidly metabolised .
Is Synephrine new Ephedrine?
Since the ban of ephedra (Ephedra sinica) by the Food and Drug Administration due to many reports and clinical associations with strokes, heart attacks, hypertension, thrombosis and other problems  there has been a flood of ephedra-free herbal weight-loss preparations. Many of them contain Citrus auratium which could in theory suppress appetite and increase fat loss but might carry the same side effects. The active nutrient found in Citrus auratium that is most interesting and most often researched is Synephrine. Synephrine is marketed as a safe alternative to ephedra but scientists warn about its potential adverse effects since it is structurally similar to ephedrine.  Findings by Haller and assistants  indicate that “new” weight loss supplement (synephrine taken orally as Citrus auratium) have similar acute cardiovascular stimulant actions as banned ephedra products and could cause adverse health effects in some individuals.
Synephrine safety concerns and side effects
Some preliminary reports have documentation concerning heart and vascular effects with the use of bitter orange and its active ingredient synephrine . One study found no effect on blood pressure after 6 weeks of ingesting 975 mg Citrus aurantium extract (6% synephrine alkaloids) . However, a study in rats showed that high doses of extracts of C. aurantium (2.5–20 mg/kg) cause ventricular arrhythmias and death (probably due to cardiovascular toxicity) . Synephrine has been associated with increased blood pressure in humans and animals and may increase cardiovascular events. 
Haller and assistants  were the first to demonstrate that synephrine, when taken orally as Citrus auratium extract, raises blood pressure in healthy humans. They suggested that when ingested in small doses it is unlikely to have significant pharmacological activity. A momentary but significant increase in heart rate was noted with ingesting both Xenadrine EFX and Advantra Z (eight fold higher dose of synephrine). When combining with other active herbal ingredients including caffeine, significant increases in blood pressure were measured.
Fugh-Berman and Myers advise : “Unless and until the short- and long-term safety and efficacy of C. aurantium extracts are established, consumers should be advised to avoid C. aurantium–containing weight-loss products, which may have adverse effects on hemodynamics and may interact with many drugs.”
Experts say that bitter orange may prove a less harmful successor to ephedra, but more research needs to be done .
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