Synopsis

Source of validity: Scientific
Rating (out of 5): 2

Synephrine is a naturally occurring alkaloid found primarily in bitter orange (Citrus aurantium). It is commonly marketed and used as a weight loss supplement, mainly after the ban of ephedra-containing products. The rationale for its use is based on its structural similarity to ephedrine and its presumed ability to stimulate thermogenesis and increase metabolic rate, potentially promoting fat loss.

There is some scientific evidence that synephrine can slightly increase resting metabolic rate and energy expenditure in humans. Several small clinical trials and meta-analyses have found modest effects on weight loss or fat oxidation when synephrine or bitter orange extract is taken, either alone or in combination with other ingredients. However, the magnitude of the effect is generally small and not always consistent across studies. The evidence is further limited by short study durations, small sample sizes, and the frequent use of multi-ingredient formulations, which makes it difficult to isolate the effect of synephrine alone.

While synephrine has a long history of use in traditional Chinese medicine (mainly for digestive issues, not weight loss), its application for weight management is recent and primarily driven by the supplement industry. Major scientific reviews (e.g., by the NIH Office of Dietary Supplements and others) conclude that current evidence is insufficient to strongly support its effectiveness for weight loss, and more rigorous, long-term studies are needed. Safety concerns, particularly regarding cardiovascular effects, have also been raised.

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