Bitter orange (citrus aurantium) is a potent thermogenic (enhancing energy expenditure and calorie burning) included in many weight-loss/fat-loss and energy-boosting supplements. A chemical called p-synephrine is responsible for its effects. The supplement increases fat breakdown at rest and oxygen consumption, energy expenditure, and speeds fat oxidation. The energy-boosting effects of these supplements promote fat loss, reduce the perception of fatigue during exercise and make workouts seem easier. Bitter orange improves performance by increasing training adherence (i.e., showing up at the gym).
Bitter orange extract is safe when taken as directed— according to a literature review of 30 human studies by Sidney Stohs from Creighton University Medical Center in Frisco, Texas. Thirteen years ago, the U.S. Food and Drug Administration (FDA) banned ephedra, an effective and popular weight loss and athletic training supplement in response to health concerns.
A study led by Nicholas Ratamess from the College of New Jersey found that supplementing p-synephrine improved squat endurance in college-age males. Subjects performed squats for six sets of 10 repetitions at 80 percent of maximum. Other studies have concluded that bitter orange extract is safe when taken as directed. (Phytotherapy Research, published online July 28, 2017)