FDA banned ephedra in 2004, and bitter orange took its place in weight-loss pills

In 2004, the Food and Drug Administration banned ephedra from dietary supplements because of serious effects on the heart ^[1]. Weight-loss and bodybuilding products moved quickly to bitter orange (Citrus aurantium), a fruit-bearing tree native to Asia whose active compound, synephrine, is similar to ephedra ^[1]. A study published in The American Journal of Medicine in September 2005 found that an "ephedra-free" weight-loss supplement raised blood pressure and heart rate in healthy adults, with effects the authors called similar to those of the banned ephedra products ^[2].

The trial was randomized, double-blind and placebo-controlled, with 10 healthy adult nonsmokers and a one-week washout between doses ^[2]. Five men and five women took part, ranging in age from 19 to 42 ^[2]. Each received a single dose of a bitter orange extract containing 46.9 mg of synephrine (Advantra Z), a multi-component supplement containing 5.5 mg of synephrine (Xenadrine EFX), or a placebo ^[2].

Compared with placebo, the multi-component product raised blood pressure; the bitter orange extract alone did not ^[2]. Peak changes came two hours after dosing: 9.6 mm Hg systolic (P = 0.047) and 9.1 mm Hg diastolic (P = 0.002) ^[2]. Heart rate rose from baseline at six hours, by 16.7 beats per minute with the multi-component product (P = 0.011) and 11.4 beats per minute with the extract (P = 0.031) ^[2]. No adverse events occurred during the study ^[2].

The authors concluded the effects were not likely caused by bitter orange alone, because a dose carrying eight times more synephrine had no effect on blood pressure ^[2]. They said the rise may be attributable to caffeine and other stimulants in the multi-component formulation ^[2]. Blood levels of synephrine peaked about 90 minutes after dosing, with a half-life of about three hours ^[2]. The authors noted the study was small, with 10 participants. Two of them disclosed serving as paid expert witnesses in litigation involving dietary supplement manufacturers ^[2].

The reference material on bitter orange lists it as possibly unsafe when taken in the larger amounts used as medicine, and says taking it with stimulants such as caffeine might increase the risk of high blood pressure, fainting, heart attack and stroke ^[1]. Headaches are also reported ^[1]. The National Collegiate Athletic Association bans synephrine for athletes ^[1]. Supplements containing synephrine have been found to contain amounts much higher than their labels state, along with other synthetic stimulants that are banned in supplements ^[1]. That reference lists caffeine, MAOIs, QT-prolonging drugs and stimulant drugs among moderate interactions ^[1]. A later review cited case reports of ischemic stroke in a 38-year-old man, exercise-induced fainting with QT prolongation in a 22-year-old woman, and a possible heart attack in a 55-year-old woman after use of bitter orange products ^[2].

Why it matters for patients

Many people managing their weight also buy supplements they can get without a prescription, and the ephedra-to-bitter-orange switch shows that removing one ingredient does not guarantee its replacement is safer. Both the human study and the bitter orange reference describe cardiovascular effects, including higher blood pressure and faster heart rate, in healthy adults rather than only in people with existing heart conditions ^[1][2].

What is on the label may not match what is in the bottle: synephrine products have been found to contain amounts higher than listed and to include other synthetic stimulants ^[1]. The WebMD monograph lists high blood pressure, irregular heartbeat, long QT interval syndrome and glaucoma among conditions where it says bitter orange should be avoided, especially alongside caffeine ^[1]. It also notes bitter orange acts like a stimulant and may interfere with surgery by raising heart rate and blood pressure ^[1].

Whether bitter orange interacts with semaglutide, tirzepatide or other GLP-1 medications has not been reported, and bitter orange does not appear on the interaction list in the reference reviewed here ^[1]. The 2005 trial did not include anyone taking a prescription weight-loss drug, so how the two might combine has not been studied in the human data described ^[2].