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Student Ohio Northern University Ada, Ohio 3423 Mapleway Drive Toledo, Ohio 43614-4137 a-hess1{at}onu.edu
Associate Professor of Pharmacy Practice Raabe College of Pharmacy Ohio Northern University
Published Online, January 18, 2005. www.theannals.com, DOI 10.1345/aph.1E249
Bitter orange extract comes from the Citrus aurantium plant. Its
active components are synephrine, N-methyltyramine, and
furocoumarins. The amount of synephrine can vary from 1% to 30% in products.
Synephrine is an 
-adrenergic agonist believed to cause weight loss by
suppressing appetite and boosting metabolism. However, it can cause
vasoconstriction through stimulation of 1 receptors,
increasing mean arterial pressure. Synephrine also causes vasoconstriction and
spasms in the coronary arteries, increasing heart rate and blood pressure.
N-Methyltyramine, another component, can increase blood pressure by
increasing norepinephrine release. The combination of synephrine and
N-methyltyramine may have additive hypertensive effects and potential
cardiotoxicity.2
The Joint National Committee on Prevention, Detection, Evaluation, and
Treatment of High Blood Pressure's Seventh Report even lists bitter orange as
a cause of resistant
hypertension.3
In one case report, a 55-year-old white female taking 300 mg of bitter orange
extract daily had an acute myocardial infarction
(AMI).4 The
patient had no history of coronary artery disease, hypertension, or
hyperlipidemia, but did have a 1.5 pack/day smoking history. Upon evaluation,
the Naranjo probability scale found that bitter orange extract was the most
likely source of her
AMI.5 One
final component in bitter orange, furocoumarins, like grapefruit, are believed
to be the component that inhibits the CYP3A4 isoenzyme. Therefore, there are
numerous potential drug interactions with drugs metabolized by CYP3A4 such as
calcium-channel blockers, anti-fungals, and
glucocorticoids.2,6
Guarana, another popular ingredient in weight-loss products, comes from the Paullinia cupana plant. The seed of guarana contains 2.5-7% caffeine (200 mg/dose). In comparison, coffee only contains 1-2% caffeine (100 mg/cup). As the dose in weight-loss supplements is titrated up, the patient may be taking as much as 1800 mg of caffeine a day. Caffeine acts as a central nervous system stimulant. In addition, it increases blood pressure and stimulates the release of catecholamines. Guarana in combination with drugs targeting the sympathetic nervous system, such as ß-adrenergic agonists and pseudoephedrine, or with other caffeine-containing substances, may have additive effects on blood pressure elevation. Guarana must be used cautiously and avoided in patients with hypertension and other cardiac conditions.2 A 25-year-old female with preexisting mitral valve prolapse drank Race 2005 Energy Blast with Guarana and Ginseng. She died of intractable ventricular fibrillation due to the high caffeine content.7
Few studies of any kind are available on either bitter orange or guarana. However, case reports regarding their safety are emerging since the weight-loss products have been reformulated. Their mechanisms of action and the case reports do not provide enough evidence about the safety of bitter orange extract and guarana. Over-the-counter weight-loss supplements should not be recommended for use until there are conclusive data.
References
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