Washington ? The Food and Drug Administration is investigating reports of liver damage in patients taking alli, the only nonprescription weight loss drug approved by the agency.

Regulators said Monday they have received more than 30 reports of liver damage in patients taking alli and Xenical, the prescription version of the drug. The reports, submitted between 1999 and October 2008, included 27 hospitalized patients, and six who suffered liver failure.

Alli and Xenical are both marketed by British drugmaker GlaxoSmithKline PLC, though Xenical is manufactured by Swiss firm Roche.

The FDA says it has not established a direct relationship between the weight loss treatments and liver injury, and advised patients to continue using the drugs as directed.

“Consumers should consult their health care professional if they are experiencing symptoms,” the agency said on its Web site. Signs of liver damage include fatigue, fever, nausea and vomiting.

A spokeswoman for GlaxoSmithKline said there is no evidence the company’s drug causes liver injury, noting that it primarily acts on the intestinal tract. She said alli’s safety has been studied in more 30,000 patients enrolled in 100 clinical studies.

“Liver changes can have many causes,” said Debbie Bolding, in a statement. “People who are overweight and obese are predisposed to liver-related disorders.”