Limited research did not find a benefit. An analysis of 3 small studies found that taking 10–54 mg of synephrine daily for 6–8 weeks had no significant effects on weight loss or fat mass.[1]
Limited research suggests that bitter orange supplements may increase fat oxidation during exercise and affect resting metabolic rate. One small study of 14 healthy adults found that taking a single dose of p-synephrine prior to one hour of cycling exercise, at a dosage of 3 mg of synephrine per kg of body weight (3 mg/kg), increased the amount of fat burned and decreased the amount of carbohydrates utilized, but did not affect total energy expenditure compared to placebo.[2]. Another small study found that 10 individuals given 50 mg of synephrine had a 65 kcal increase in their resting metabolic rate compared to placebo, but this result was not significant.[3]