Food and Drug Administration officials on Saturday warned that GlaxoSmithKline's fake versions of over-the-counter diet pill called Alli contained high levels of a prescription weight loss ingredient called sibutramine that was dangerous.

Dr Janet Woodcock, head of the FDA's drug unit, told reporters that "The amount of sibutramine in the counterfeit Alli poses a serious health risk to some individuals. A person taking the counterfeit Alli as directed would be exposed to twice the maximum prescription dose of sibutramine every day.”

The FDA warned earlier this week that sibutramine could raise risks of heart attacks and strokes if used by people having a history of cardiovascular disease.

In Europe Abbott agreed to suspend sales after regulators concluded sibutramine was risky.

The fake version was purchased on eBay Inc. and other web sites. The bogus version was in a 120-count refill kit containing 60-milligram capsules.

The agency has warned that consumers should check that the product bought is genuine immediately discarding any fake products.