Synephrine is a nutrient that comes from bitter oranges and is often used in pre-workout, energy, and weight loss formulas. There have been over 20 studies done with over 360 people with synephrine. It works via adrenergic receptors in the brain, and is able to provide a noticeable boost for most people. The ideal dosage tends to vary from person to person, so it's a good idea to start low and customize the dose based on your needs. The evidence shows that bitter orange extract causes its effect with little or no increase in heart rate and blood pressure, and no alterations of electrocardiographic data, serum chemistry, blood cell counts or urinalysis. (1)
Some people have reported that they do feel an increase in heart rate with synephrine, which is why a lower dose the first few times is recommended. The safety track for synephrine when used as directed is excellent. (2,3)Synephrine has been shown to increase lipolysis (the breaking down of fatty acids) and has a positive effect on insulin sensitivity, although more research is needed. Synephrine was shown to increase resting metabolic rate and energy expenditure, which results in modest amounts of weight loss. Subjects took synephrine for 6 to 12 weeks to see those results.(1)
There was another small study done with 10 individuals receiving 50mgs of synephrine per day. The results showed a 65kcal increase in RMR compared to placebo. (4) Using synephrine with small doses of caffeine, cayenne, gymnema, green tea etc, would likely increase the results. It's not a good idea to take more of synephrine though hoping for better results. It's best used in conjunction with other weight loss nutrients. Bitter orange is often used right before working out to impart energy and help boost the metabolic rate.
Suggested use 500-600mgs mgs twice a day with water