The Food and Drug Administration said the maker of the dietary supplement has agreed to recall 14 Hydroxycut products. Available in grocery stores and pharmacies, Hydroxycut is advertised as made from natural ingredients. At least 9 million packages were sold last year, the FDA said.

    Dr. Linda Katz of the FDA's food and nutrition division said the agency has received 23 reports of liver problems, including the death of a 19-year-old boy living in the Southwest. The teenager died in 2007, and the death was reported to the FDA this March.

    Other patients experienced symptoms ranging from jaundice, or yellowing of the skin, to liver failure. One received a transplant and another was placed on a list to await a new liver.

    There was no immediate comment from the U.S. distributor of the diet pill, Iovate Health Sciences, headquartered near Buffalo, N.Y. Made by a Canadian company, Hydroxycut is used by people trying to shed pounds and by body builders to sharpen their muscles.

    Dietary supplements aren't as tightly regulated by the government as medications. Manufacturers don't need to prove to the FDA that their products are safe and effective before they can sell them to consumers. But regulators monitor aftermarket reports for signs of trouble, and in recent years companies have been put under stricter requirements to alert the FDA when they learn of problems.

    Katz said it has taken so long to get a handle on the Hydroxycut problem because the cases of liver damage were rare and the FDA has no authority to review supplements before they're marketed. "Part of the problem is that the FDA looks at dietary supplements from a post-market perspective, and an isolated incident is often difficult to follow," she said.

    The FDA relies on voluntary reports to detect such problems, and many cases are never reported, officials acknowledge.

    Health officials said they have been unable to determine which Hydroxycut ingredients are potentially toxic, partially because the formulation of the products has changed several times. A medical journal report last month raised questions about one ingredient, hydroxycitric acid, derived from a tropical fruit. The article said it could potentially damage the liver.

    美國食品和藥物管理局稱，生產商已同意回收14種減肥藥。這種產品在雜貨店和藥店里都可以買到.據稱,14種減肥藥是由天然原料制成的。去年至少有9萬包已經售出.

    食品及藥物管理局的食品和營養司的琳達卡茨醫生表示,該司已收到23份反映肝臟損害的報告，其中包括居住西南地區19歲男子2007年死于肝臟衰竭。并于本年3月報告到食品及藥物管理局.

    其他病人的癥狀，包括黃疸，皮膚發黃，肝功能衰竭。其中一人接收了肝功移植,另一人被列在等待移植的名單里.

    美國減肥藥分銷商對此沒有立即發表評論,總部設在紐約水牛城附近，藥品是由加拿大公司生產.這種藥品是用來迅速減輕體重,增強體力.達到健美的目的.

    藥品并沒有受到政府的嚴格限制。制造商并不需要向美國食品及藥物管理局說明他們的產品是安全和有效的,才可以出售給消費者。但監管機構監測到了售后的麻煩問題，并在最近幾年公司一直在實行更嚴格的要求，提醒美國食品和藥物管理局當他們了解的問題。

    卡茨說，花費了很長時間才處理完減肥藥的問題，因為該案件是罕見的肝損害,在銷售該藥品之前,美國食品及藥物管理局又沒有權力審查. “美國食品及藥物管理局著眼于了解消費者的反映，個別案件往往被忽略了。”

    美國食品及藥物管理局是通過顧客的反映才能發現問題，但是,許多情況下，此類案件從來沒有報道過,官員承認。

    衛生官員表示，他們一直無法確定哪些減肥藥可能含有毒成分，部分原因是產品工藝流程改變了好幾次。上個月醫學雜志報對羥基酸提出了異議，它取自熱帶水果,有可能會損害肝臟,文章說.