WASHINGTON (AP) -- Some 16,000 customer complaints about the popular Metabolife brand of ephedra are not enough to prove whether the herb caused dozens of heart attacks and strokes, some fatal, congressional investigators say.

The report released Wednesday doesn't mean ephedra is safe, the Food and Drug Administration stressed: There is evidence from other sources that the pills can cause serious health problems.

Armed with reports of more than 100 deaths and thousands of side effects linked to ephedra use, the FDA two months ago pledged to put warning labels on every bottle that say the amphetamine-like stimulant can cause heart attacks, strokes or even kill.

The General Accounting Office, Congress' investigative arm, examined 16,000 records of phone calls from ephedra customers with health complaints turned over to the Justice Department last year by Metabolife International.

The GAO counted 92 reports of serious side effects -- including 18 heart attacks, 26 strokes, 43 seizures and five deaths -- made by Metabolife customers to a company hot line.

The GAO concluded that there was far too little information to definitively link any of the reports to the pills because patients, not doctors, reported the problems, and Metabolife employees sometimes recorded just a single word from each phone call.

The FDA noted that the Rand Corp. also reviewed Metabolife's records, and called some of the cases "sentinel events" that warrant further investigation. Also, most of the agency's evidence is from other sources compiled before Metabolife revealed its records.

"Today's report does nothing to change FDA's heightened concern that dietary supplements containing ephedra may present a significant and unreasonable risk of illness and injury," the agency said.

Metabolife insisted the GAO report supports its position "that ephedrine-containing products such as Metabolife 356 are safe and effective when used as directed."

Rep. Dan Burton, who requested the report, said the GAO's findings show the government needs to establish a federal tracking system for consumer complaints about any dietary supplement.

The FDA decision came just weeks after Baltimore Orioles pitcher Steve Bechler died after using ephedra. Health and Human Services Secretary Tommy Thompson has advised Americans, especially those who exercise, not to take the herb.

The American Heart Association and other health groups have urged a full ban on ephedra sales, calls the FDA currently is evaluating.

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