from CNN.com

WASHINGTON (Reuters) -- The U.S. Food and Drug Administration is gathering evidence on the safety of several alternatives to ephedra, the weight-loss herb the agency banned a week ago, the agency's top official said Monday.

Acting FDA Commissioner Lester Crawford said regulators are also compiling data on three other supplements, including kava, a dried root often used as a relaxant that has been linked to liver damage.

"Never again will one of these [supplements] as bad as ephedra take two years" to ban, Crawford said.

The FDA is collecting research results, reports of health problems and other information to help officials decide whether to ban other supplements, he said.

"We've started the clock ticking. Maybe it will result in an ephedra-like decision for some of these [or] maybe not" Crawford said in a speech to the American Society for Pharmacology and Experimental Therapeutics in Washington.

Since the agency announced the ephedra ban last December, a number of manufacturers have sought to fill the void with other products, including so-called bitter orange, or Citrus aurantium. The ban took effect last Monday.

Bitter orange contains several substances that produce an ephedra-like stimulation and have been shown to increase blood pressure. But Crawford said it was "too soon to say" whether it should be removed from the market.

While there are similarities, "the concerns are being overblown," said Michael McGuffun, president of the American Herbal Products Association. Many products put forward to replace ephedra are caffeine-based, he said.

The FDA is also compiling data on usnic acid, Crawford said. The lichen-produced chemical is used in some products touting weight control and has been linked to liver damage.

Pyrrolizidine alkaloids, compounds found in plants, can be toxic and are also under review, he said.

While most supplements "are probably safe" when used correctly, the industry's diversity and ability to quickly devise new products make it difficult to regulate, Crawford said.

But the recent ephedra court ruling favoring the FDA gave the agency strength to act against other supplements in the future, Crawford added.

The Council for Responsible Nutrition, a supplement industry group, supports FDA's safety efforts, President Annette Dickinson said, adding that many companies have already placed warnings on kava products.

The FDA last month recommended that the National Institutes of Health make studying these four supplements a priority.

Paul Coates, head of NIH's Office of Dietary Supplements, said the institute's ephedra studies put steps in place to evaluate similar products but would not say if any studies were planned.