Synephrine is the primary alkaloid in bitter orange extract that is derived from the immature fruits of Citrus aurantium. Synephrine was big about ten years ago with the pre-workout drink “Ultimate Orange” but it seems like synephrine is making a comeback in the bodybuilding world. Synephrine was invented when ephedrine became banned as a supplement. Synephrine is structurally similar to adrenaline, noradrenaline, and ephedrine. Several studies have confirmed the metabolic effects of synephrine that are useful for bodybuilders such as: enhancing thermogenesis. Synephrine is widely used in combination with caffeine and other ingredients in products designed to support weight management.
A previous study reported that 20mg of synephrine with 325 mg of caffeine increased energy expenditure in humans. In a meta-analysis of human studies involving p-synephrine alone or in combination with other nutrients increased resting metabolic rate and energy expenditure by up to ~13 %, and led to modest reductions in body weight. Many supplement companies advocate synephrine and caffeine for weight loss, but according to a new study from the Department of Health and Exercise Science from the College of New Jersey, published in the Journal of the International Society of Sports Nutrition, synephrine can enhance repetitions performed in the gym. There are not any studies to date examining the validity of synephrine for performance enhancement, so researchers wanted to put synephrine to the test.