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.

    美国食品和药物管理局称，生产商已同意回收14种减肥药。这种产品在杂货店和药店里都可以买到.据称,14种减肥药是由天然原料制成的。去年至少有9万包已经售出.

    食品及药物管理局的食品和营养司的琳达卡茨医生表示,该司已收到23份反映肝脏损害的报告，其中包括居住西南地区19岁男子2007年死于肝脏衰竭。并于本年3月报告到食品及药物管理局.

    其他病人的症状，包括黄疸，皮肤发黄，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单里.

    美国减肥药分销商对此没有立即发表评论,总部设在纽约水牛城附近，药品是由加拿大公司生产.这种药品是用来迅速减轻体重,增强体力.达到健美的目的.

    药品并没有受到政府的严格限制。制造商并不需要向美国食品及药物管理局说明他们的产品是安全和有效的,才可以出售给消费者。但监管机构监测到了售后的麻烦问题，并在最近几年公司一直在实行更严格的要求，提醒美国食品和药物管理局当他们了解的问题。

    卡茨说，花费了很长时间才处理完减肥药的问题，因为该案件是罕见的肝损害,在销售该药品之前,美国食品及药物管理局又没有权力审查. “美国食品及药物管理局着眼于了解消费者的反映，个别案件往往被忽略了。”

    美国食品及药物管理局是通过顾客的反映才能发现问题，但是,许多情况下，此类案件从来没有报道过,官员承认。

    卫生官员表示，他们一直无法确定哪些减肥药可能含有毒成分，部分原因是产品工艺流程改变了好几次。上个月医学杂志报对羟基酸提出了异议，它取自热带水果,有可能会损害肝脏,文章说.