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 say they have received more than 30 reports of liver damage in patients taking Alli and Xenical, the prescription version of the drug. Twenty-seven patients had to be hospitalized, and six suffered liver failure.

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

The FDA says it has not established a definitive relationship between the weight loss drugs and liver injury.

The agency says patients should continue using the drugs as directed