Does synephrine (bitter orange extract) help you lose weight?

Short answer

No. It burned about 4 g more fat during 1 hour of exercise, but in trials lasting 6 to 8 weeks, body weight and body fat did not differ from a fake pill. In 75 people who took it for 8 weeks, blood pressure went up.

Does synephrine (bitter orange extract) help you lose weight?
'Orange peel compound → more fat burned → weight loss' — does this formula hold?
Synephrine is a compound found in the peel of unripe bitter oranges. It replaced the banned stimulant ephedrine in many diet and pre-workout supplements. We checked whether it burns more fat, and whether people actually lose weight.
Does it burn more fat?
During exercise, it did
18 people took synephrine (210 mg for a 70 kg (154 lb) person) or a fake pill, then cycled at steadily rising effort. On synephrine, their peak fat burning per minute rose from 0.29 g to 0.40 g. At rest, and in total calories burned, there was no difference.
So how much more fat?
About 4 g in 1 hour of exercise
14 people took the same amount and cycled for 1 hour. Fat burned rose from 33.6 g to 37.3 g, an extra 3.7 g, while calories burned (686 kcal vs 698 kcal) did not differ. 3.7 g is about 33 kcal. At that rate, burning 1 kg of extra fat would take about 270 one-hour sessions.
Did body weight drop?
No difference even after 6 to 8 weeks
A 2022 analysis that pooled 18 synephrine trials found 3 trials where people took 10 to 54 mg a day for 6 to 8 weeks. Body weight and fat mass did not differ from a fake pill. All 3 trials included exercise. Lean mass (everything except fat) did not change either.
Blood pressure went up instead
75 people over 8 weeks: top number 6.37 higher
In the same analysis, 75 people who took 10 to 49 mg a day for 8 weeks had a top blood pressure number 6.37 higher and a bottom number 4.33 higher than with a fake pill. That is like 120 becoming about 126. In 18 people who took 49 mg once, heart rate and blood pressure did not change. Blood pressure rose with continued use.
Reported cases
Heart problems in 2 people with no risk factors
One person had a heart attack from a blocked heart artery within hours of taking a synephrine-containing diet supplement. Another took a bitter orange supplement for 1 week, then developed a very fast heartbeat and heart muscle damage. Neither had any risk factors for heart disease.
Summary: the extra fat burn was small, and no weight came off
The formula breaks at 'more fat burned → weight loss'
Synephrine burned about 4 g more fat in 1 hour of exercise, but trials lasting 6 to 8 weeks found no difference in body weight or body fat. In 75 people over 8 weeks, the top blood pressure number rose by 6.37. The weight did not come off; only blood pressure went up.