Bitter orange extract is derived from the immature fruit of the Seville orange and contains several potent plant compounds, including p-synephrine, which is the main extract used in dietary supplements for weight loss. Other compounds found in bitter orange extract include limonene, octopamine, and various flavonoids.
Unfortunately, despite being one of the most commonly used extracts, it's very often misused. The reason is that synephrine only makes up around 0.1–0.3% of bitter orange  and for this particular compound to be effective (according to the few clinical trials that have shown positive results) it needs to be dosed in 30-100mg per day. [2,3,4]
This means that a lot of supplements that state that they contain "bitter orange extract" are simply misleading the consumer as in most cases these extracts have no standardization of synephrine, meaning that the end user would need to consume 30 grams a day of bitter orange extract, and considering the fact that a single supplement capsule can only contain 1 gram, this isn't viable.
The reason for it's popularity is that if dosed correctly it is one of relatively few natural thermogrenic compounds (in that they raise thermogenesis, or the rate at which your body burns calories) that don't contain stimulants. This sounds great, but they are also relatively ineffective when compared to other sorts of weight loss aids, such as stimulants (like caffeine) or appetite suppressants like glucomannan.
It is essential to differentiate between p-synephrine, the primary protoalkaloid in bitter orange extract, and m-synephrine (phenylephrine), which is a synthetic derivative. The cardiovascular effects attributed to m-synephrine should not be assumed to apply to bitter orange extract or p-synephrine.
Efficacy of Bitter Orange Extract for Weight Loss
The efficacy of bitter orange extract for weight loss has been studied in various clinical trials. These studies have assessed its impact on resting metabolic rate, energy expenditure, and overall weight loss. In general, bitter orange extract, whether consumed alone or in combination with other herbal ingredients, has shown modest increases in weight loss when given for six to 12 weeks.  However, it should be noted that these were well standardized extracts and not commercially available.
In a study by Kalman et al. (2002), overweight subjects consumed a weight loss product containing bitter orange extract, yerba mate, grape seed, green tea, and ginger root for eight weeks. The treated group experienced significant weight loss compared to the control group, along with an increase in basal metabolic rate. Similar findings were observed in other studies where bitter orange extract was combined with exercise and calorie restriction.
Bitter Orange as a Mild Appetite Suppressant
In addition to its potential effects on metabolism and energy expenditure, bitter orange extract has also been suggested to have mild appetite-suppressing properties. Some studies have reported reduced feelings of hunger and improved satiety with the consumption of bitter orange extract-containing products. However, the exact mechanisms behind these effects are still not fully understood, and more research is needed to determine the true impact of bitter orange extract on appetite regulation. It also has not been shown to be nearly as effective as other natural appetitite suppressants.
Safety and Side Effects of Bitter Orange Extract: Human Studies
Numerous studies have been conducted to assess the safety and efficacy of bitter orange extract, particularly when used for weight loss purposes. These studies have involved both overweight/obese individuals and healthy subjects. In general, bitter orange extract, either in the form of p-synephrine alone or combined with other herbal ingredients, has not been found to produce significant adverse events such as an increase in heart rate or blood pressure. Electrocardiographic data, serum chemistry, blood cell counts, and urinalysis have also not shown significant changes with the consumption of bitter orange extract.
When it comes to weight loss, bitter orange extract has shown promising results in some studies. Increases in resting metabolic rate and energy expenditure have been observed with the consumption of p-synephrine alone or in combination products. Modest weight loss has also been reported when bitter orange extract-containing products were consumed for a period of six to twelve weeks. However, it is important to note that longer-term studies are needed to further assess the efficacy of these products and confirm their safety under extended use.
Other Uses for Bitter Orange
Beyond its potential role in weight loss, bitter orange extract has been investigated for its other health benefits. Some studies have suggested that the plant compounds found in bitter orange, such as limonene, may possess natural anti-inflammatory and antiviral properties.  Population studies have also indicated a potential preventive effect of limonene against certain types of cancer, although further research is needed to confirm these findings. Bitter orange extract has also been used in traditional medicine to treat gastrointestinal issues, anxiety, and epilepsy, although the scientific evidence supporting these uses is limited.
Bitter Orange Weight Loss Conclusion
While the existing studies provide valuable insights into the safety and efficacy of bitter orange extract, further research is needed to fully understand its potential benefits and risks. Studies with larger sample sizes, longer durations, and diverse populations are necessary to establish the long-term effects of bitter orange extract on weight management and overall health. Additionally, more research is needed to explore the mechanisms of action underlying the observed effects of bitter orange extract, including its potential effects on metabolism, appetite regulation, and other physiological processes.
1 - https://pubmed.ncbi.nlm.nih.gov/15862657/
2 - https://pubmed.ncbi.nlm.nih.gov/23354394/
3 - https://pubmed.ncbi.nlm.nih.gov/15536458/
4 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5655712/
5 - https://pubmed.ncbi.nlm.nih.gov/22991491/
6 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3444973/
7 - https://pubmed.ncbi.nlm.nih.gov/18593176