Similar, but not identical, in structure to ephedrine, synephrine may suppress appetite and increase metabolic rate without serious negative side effects. Synephrine specifically attaches to Beta-3 cell receptors, which increases the rate of fat release from body stores and increases the resting metabolic rate (thermogenesis). Because bitter orange binds only to Beta-3, it does not cause elevated heart rate or blood pressure, anxiety, or insomnia.

In clinical studies, bitter orange extract has been found to increase resting metabolic rates, which promotes weight loss. In an eight-week study, the effect of bitter orange extract on obese subjects was measured. The study concluded that bitter orange extract induced an 11% increase in the subjects’ resting metabolic rate as well as a 12% increase of metabolic rate after ingestion of a meal.

Additional studies have found that caffeine prevents the body from becoming resistant to the effects of synephrine. Caffeine combined with synephrine helps stimulate other cellular receptors that are important to weight loss.