How does bitter orange work?

The synephrine in bitter oranges is thought to work as a sympathetic adrenergic agonist, stimulating receptors involved in the “fight or flight” response. These effects stimulate the cardiovascular system resulting in increased heart rate and blood pressure. Also, these effects may stimulate metabolism, resting metabolic rate and lipolysis (breakdown of fat). Appetite may also be suppressed via slowed movement of food through the gastrointestinal tract.^{[1] [2]}