"The two work much the same way. Citrus aurantium will boost metabolic rate and, indirectly, cause the breakdown of fat," said Dennis Jones, a Vermont scientist who began working on Citrus aurantium 10 years ago and created the brand called Advantra Z.
Some herb makers say that bitter orange will work as well as ephedra but without affecting the central nervous system or the heart. "It has the same effects in the periphery of the body, but it's weaker," said Jones. "It's nowhere near as potent."
Gurley agrees that Citrus aurantium by itself probably has little effect. But herbal weight-loss products are typically mixtures of various herbs, such as caffeine to boost metabolism and herbs that act as diuretics. Blending several herbs typically increases effectiveness. In the same manner, mixing Citrus aurantium with other herbs may improve its potency, making it more effective and, potentially, more dangerous to some users, he said.
"I think you'll see the same types of problems as ephedra," he said. "Normally, synephrine is not well-absorbed in the gastrointestinal tract. But there are compounds in some of these products that could aid absorption."
For example, Gurley said, the herbs guarana and green tea have the potential to exacerbate the activity of Citrus aurantium.
Another potential problem with Citrus aurantium is that it could interact with a host of prescription drugs, said Gurley, who is studying the herb. Citrus aurantium inhibits an enzyme, known as CYP3A4, in the small intestine that can alter the metabolism of drugs, boosting their activity.
"We know this enzyme is responsible for the metabolic activity of 50% of all prescription medications," he said. "We know that Seville orange juice can wipe out those enzymes. It would be reasonable to think that these concentrated extracts would do the same."
Both Jones and McManus said the studies they've seen, performed at McGill University in Montreal and by Herbalife, have not shown any side effects.
But until more is known about Citrus aurantium weight-loss products, however, Gurley urges caution. "It's like where we were six years ago with ephedra."
In the meantime, whether the federal government pulls ephedra off the market -- as the American Medical Assn. recently urged -- remains to be seen. The safety report ordered by the Bush administration is due out early next year and could help government and industry leaders reach a consensus on how to best regulate ephedra. The Rand Corp. of Santa Monica is developing the report.
"That report is going to be the defining word, or something close to it," Blumenthal said. "I think the Rand report constitutes a very good development in the saga of ephedra because it's an independent review."
Leaders in the supplement industry continue to defend ephedra's safety when taken by healthy individuals in the recommended doses. Industry representatives are working with the FDA to create labeling for all ephedra products that would state proper dosage and which individuals should avoid taking the herb, said Michael McGuffin, president of the American Herbal Products Assn., a national trade organization for the herb supplement industry.
But, Blumenthal notes, some herb supplement makers feel the entire herbal field is being dragged down by the safety questions surrounding ephedra.
"Some companies do not sell ephedra and don't care if it's regulated into a corner or removed from the market," he said. "They just want to see the problem go away because they see the constant negative attention as being ultimately deleterious to the entire industry."